PANDA Phase One
G. Barucca, F. Davì, G. Lancioni, P. Mengucci, L. Montalto, P. P. Natali, N. Paone, D. Rinaldi, L. Scalise, B. Krusche, M. Steinacher, Z. Liu, C. Liu, B. Liu, X. Shen, S. Sun, G. Zhao, J. Zhao, M. Albrecht, W. Alkakhi, S. Bökelmann, S. Coen, F. Feldbauer, M. Fink, J. Frech, V. Freudenreich, M. Fritsch, J. Grochowski, R. Hagdorn, F.H. Heinsius, T. Held, T. Holtmann, I. Keshk, H. Koch, B. Kopf, M. Kümmel, M. Kü?ner, J. Li, L. Linzen, S. Maldaner, J. Oppotsch, S. Pankonin, M. Pelizäus, S. Pflüger, J. Reher, G. Reicherz, C. Schnier, M. Steinke, T. Triffterer, C. Wenzel, U. Wiedner, H. Denizli, N. Er, U. Keskin, S. Yerlikaya, A. Yilmaz, R. Beck, V. Chauhan, C. Hammann, J. Hartmann, B. Ketzer, J. Müllers, B. Salisbury, C. Schmidt, U. Thoma, M. Urban, A. Bianconi, M. Bragadireanu, D. Pantea, S. Rimjaem, M. Domagala, G. Filo, E. Lisowski, F. Lisowski, M. Micha?ek, P. Pozna?ski, J. P?ażek, K. Korcyl, P. Lebiedowicz, K. Pysz, W. Schäfer, A. Szczurek, M. Firlej, T. Fiutowski, M. Idzik, J. Moron, K. Swientek, P. Terlecki, G. Korcyl, R. Lalik, A. Malige, P. Moskal, K. Nowakowski, W. Przygoda, N. Rathod, P. Salabura, J. Smyrski, I. Augustin, R. Böhm, I. Lehmann, et al. (324 additional authors not shown)
EEPJ manuscript No. (will be inserted by the editor)
PANDA Phase One
PANDA collaborationG. Barucca , F. Davì , G. Lancioni , P. Mengucci , L. Montalto , P. P. Natali , N. Paone , D. Rinaldi , L. Scalise ,B. Krusche , M. Steinacher , Z. Liu , C. Liu , B. Liu , X. Shen , S. Sun , G. Zhao , J. Zhao , M. Albrecht ,W. Alkakhi , S. Bökelmann , S. Coen , F. Feldbauer , M. Fink , J. Frech , V. Freudenreich , M. Fritsch ,J. Grochowski , R. Hagdorn , F.H. Heinsius , T. Held , T. Holtmann , I. Keshk , H. Koch , B. Kopf , M. Kümmel ,M. Küßner , J. Li , L. Linzen , S. Maldaner , J. Oppotsch , S. Pankonin , M. Pelizäus , S. Pflüger , J. Reher ,G. Reicherz , C. Schnier , M. Steinke , T. Triffterer , C. Wenzel , U. Wiedner , H. Denizli , N. Er , U. Keskin ,S. Yerlikaya , A. Yilmaz , R. Beck , V. Chauhan , C. Hammann , J. Hartmann , B. Ketzer , J. Müllers ,B. Salisbury , C. Schmidt , U. Thoma , M. Urban , A. Bianconi , M. Bragadireanu , D. Pantea , S. Rimjaem ,M. Domagala , G. Filo , E. Lisowski , F. Lisowski , M. Michałek , P. Poznański , J. Płażek , K. Korcyl ,P. Lebiedowicz , K. Pysz , W. Schäfer , A. Szczurek , M. Firlej , T. Fiutowski , M. Idzik , J. Moron ,K. Swientek , P. Terlecki , G. Korcyl , R. Lalik , A. Malige , P. Moskal , K. Nowakowski , W. Przygoda ,N. Rathod , P. Salabura , J. Smyrski , I. Augustin , R. Böhm , I. Lehmann , L. Schmitt , V. Varentsov ,M. Al-Turany , A. Belias , H. Deppe , R. Dzhygadlo , H. Flemming , A. Gerhardt , K. Götzen , A. Heinz ,P. Jiang , R. Karabowicz , S. Koch , U. Kurilla , D. Lehmann , J. Lühning , U. Lynen , H. Orth ,K. Peters , J. Ritman , , G. Schepers , C. J. Schmidt , C. Schwarz , J. Schwiening , A. Täschner ,M. Traxler , B. Voss , P. Wieczorek , V. Abazov , G. Alexeev , M. Yu. Barabanov , V. Kh. Dodokhov ,A. Efremov , A. Fechtchenko , A. Galoyan , G. Golovanov , E. K. Koshurnikov , Y. Yu. Lobanov , A.G. Olshevskiy , A. A. Piskun , A. Samartsev , S. Shimanski , N. B. Skachkov , A. N. Skachkova , E.A. Strokovsky , V. Tokmenin , V. Uzhinsky , A. Verkheev , A. Vodopianov , N. I. Zhuravlev , D. Watts ,M. Böhm , W. Eyrich , A. Lehmann , D. Miehling , M. Pfaffinger , K. Seth , T. Xiao , A. Ali , A. Hamdi ,M. Himmelreich , M. Krebs , S. Nakhoul , F. Nerling , , P. Gianotti , V. Lucherini , G. Bracco ,S. Bodenschatz , K.T. Brinkmann , L. Brück , S. Diehl , V. Dormenev , M. Düren , T. Erlen , C. Hahn ,A. Hayrapetyan , J. Hofmann , S. Kegel , F. Khalid , I. Köseoglu , A. Kripko , W. Kühn , V. Metag ,M. Moritz , M. Nanova , R. Novotny , P. Orsich , J. Pereira-de-Lira , M. Sachs , M. Schmidt , R. Schubert ,M. Strickert , T. Wasem , H.G. Zaunick , E. Tomasi-Gustafsson , D. Glazier , D. Ireland , B. Seitz ,R. Kappert , M. Kavatsyuk , H. Loehner , J. Messchendorp , V. Rodin , K. Kalita , G. Huang , D. Liu ,H. Peng , H. Qi , Y. Sun , X. Zhou , M. Kunze , K. Azizi , , A. T. Olgun , Z. Tavukoglu , A. Derichs ,R. Dosdall , W. Esmail , A. Gillitzer , F. Goldenbaum , D. Grunwald , L. Jokhovets , J. Kannika ,P. Kulessa , S. Orfanitski , G. Perez-Andrade , D. Prasuhn , E. Prencipe , J. Pütz , E. Rosenthal ,S. Schadmand , R. Schmitz , A. Scholl , T. Sefzick , V. Serdyuk , T. Stockmanns , D. Veretennikov ,P. Wintz , P. Wüstner , H. Xu , Y. Zhou , X. Cao , Q. Hu , Y. Liang , V. Rigato , L. Isaksson ,P. Achenbach , O. Corell , A. Denig , M. Distler , M. Hoek , W. Lauth , H. H. Leithoff , H. Merkel ,U. Müller , J. Petersen , J. Pochodzalla , S. Schlimme , C. Sfienti , M. Thiel , S. Bleser , M. Bölting ,L. Capozza , A. Dbeyssi , A. Ehret , R. Klasen , R. Kliemt , F. Maas , C. Motzko , O. Noll , D. RodríguezPiñeiro , F. Schupp , M. Steinen , S. Wolff , I. Zimmermann , D. Kazlou , M. Korzhik , O. Missevitch ,P. Balanutsa , V. Chernetsky , A. Demekhin , A. Dolgolenko , P. Fedorets , A. Gerasimov , A. Golubev ,A. Kantsyrev , D. Y. Kirin , N. Kristi , E. Ladygina , E. Luschevskaya , V. A. Matveev , V. Panjushkin , A.V. Stavinskiy , A. Balashoff , A. Boukharov , M. Bukharova , O. Malyshev , E. Vishnevsky , D. Bonaventura ,P. Brand , B. Hetz , N. Hüsken , J. Kellers , A. Khoukaz , D. Klostermann , C. Mannweiler , S. Vestrick ,D. Bumrungkoh , C. Herold , K. Khosonthongkee , C. Kobdaj , A. Limphirat , K. Manasatitpong ,T. Nasawad , S. Pongampai , T. Simantathammakul , P. Srisawad , N. Wongprachanukul , Y. Yan , C. Yu ,X. Zhang , W. Zhu , E. Antokhin , A. Yu. Barnyakov , K. Beloborodov , V. E. Blinov , I. A. Kuyanov ,S. Pivovarov , E. Pyata , Y. Tikhonov , A. E. Blinov , S. Kononov , E. A. Kravchenko , M. Lattery ,G. Boca , D. Duda , M. Finger , M. Finger, Jr. , A. Kveton , I. Prochazka , M. Slunecka , M. Volf ,V. Jary , O. Korchak , M. Marcisovsky , G. Neue , J. Novy , L. Tomasek , M. Tomasek , M. Virius ,V. Vrba , V. Abramov , S. Bukreeva , S. Chernichenko , A. Derevschikov , V. Ferapontov , Y. Goncharenko ,A. Levin , E. Maslova , Y. Melnik , A. Meschanin , N. Minaev , V. Mochalov , , V. Moiseev , D. Morozov ,L. Nogach , S. Poslavskiy , A. Ryazantsev , S. Ryzhikov , P. Semenov , , I. Shein , A. Uzunian ,A. Vasiliev , , A. Yakutin , S. Belostotski , G. Fedotov , A. Izotov , S. Manaenkov , O. Miklukho , a r X i v : . [ h e p - e x ] J a n B. Cederwall , M. Preston , P.E. Tegner , D. Wölbing , K. Gandhi , A. K. Rai , S. Godre , V. Crede ,S. Dobbs , P. Eugenio , M. P. Bussa , S. Spataro , D. Calvo , P. De Remigis , A. Filippi , G. Mazza ,R. Wheadon , F. Iazzi , A. Lavagno , A. Akram , H. Calen , W. Ikegami Andersson , T. Johansson ,A. Kupsc , P. Marciniewski , M. Papenbrock , J. Regina , J. Rieger , K. Schönning , M. Wolke , A. Chlopik ,G. Kesik , D. Melnychuk , J. Tarasiuk , , M. Wojciechowski , S. Wronka , B. Zwieglinski , C. Amsler ,P. Bühler , J. Marton , S. Zimmermann andC.S. Fischer , J. Haidenbauer , C. Hanhart , M.F.M. Lutz , , and Sinéad M. Ryan Università Politecnica delle Marche-Ancona,
Ancona , Italy Universität Basel,
Basel , Switzerland Institute of High Energy Physics, Chinese Academy of Sciences,
Beijing , China Ruhr-Universität Bochum, Institut für Experimentalphysik I,
Bochum , Germany Department of Physics, Bolu Abant Izzet Baysal University,
Bolu , Turkey Rheinische Friedrich-Wilhelms-Universität Bonn,
Bonn , Germany Università di Brescia,
Brescia , Italy Institutul National de C&D pentru Fizica si Inginerie Nucleara "Horia Hulubei",
Bukarest-Magurele , Romania Chiang Mai University,
Chiang Mai , Thailand University of Technology, Institute of Applied Informatics,
Cracow , Poland IFJ, Institute of Nuclear Physics PAN,
Cracow , Poland AGH, University of Science and Technology,
Cracow , Poland Instytut Fizyki, Uniwersytet Jagiellonski,
Cracow , Poland FAIR, Facility for Antiproton and Ion Research in Europe,
Darmstadt , Germany GSI Helmholtzzentrum für Schwerionenforschung GmbH,
Darmstadt , Germany Joint Institute for Nuclear Research,
Dubna , Russia University of Edinburgh,
Edinburgh , United Kingdom Friedrich-Alexander-Universität Erlangen-Nürnberg,
Erlangen , Germany Northwestern University,
Evanston , U.S.A. Goethe-Universität, Institut für Kernphysik,
Frankfurt , Germany INFN Laboratori Nazionali di Frascati,
Frascati , Italy Dept of Physics, University of Genova and INFN-Genova,
Genova , Italy Justus-Liebig-Universität Gießen II. Physikalisches Institut,
Gießen , Germany IRFU, CEA, Université Paris-Saclay,
Gif-sur-Yvette Cedex , France University of Glasgow,
Glasgow , United Kingdom University of Groningen,
Groningen , Netherlands Gauhati University, Physics Department,
Guwahati , India University of Science and Technology of China,
Hefei , China Universität Heidelberg,
Heidelberg , Germany Department of Physics, Dogus University,
Istanbul , Turkey Istanbul Okan University,
Istanbul , Turkey Forschungszentrum Jülich, Institut für Kernphysik,
Jülich , Germany Chinese Academy of Science, Institute of Modern Physics,
Lanzhou , China INFN Laboratori Nazionali di Legnaro,
Legnaro , Italy Lunds Universitet, Department of Physics,
Lund , Sweden Johannes Gutenberg-Universität, Institut für Kernphysik,
Mainz , Germany Helmholtz-Institut Mainz,
Mainz , Germany Research Institute for Nuclear Problems, Belarus State University,
Minsk , Belarus Institute for Theoretical and Experimental Physics named by A.I. Alikhanov of National Research Centre "KurchatovInstitute”,
Moscow , Russia Moscow Power Engineering Institute,
Moscow , Russia Westfälische Wilhelms-Universität Münster,
Münster , Germany Suranaree University of Technology,
Nakhon Ratchasima , Thailand Nankai University,
Nankai , China Budker Institute of Nuclear Physics,
Novosibirsk , Russia Novosibirsk State University,
Novosibirsk , Russia University of Wisconsin Oshkosh,
Oshkosh , U.S.A. Dipartimento di Fisica, Università di Pavia, INFN Sezione di Pavia,
Pavia , Italy University of West Bohemia,
Pilsen , Czech Charles University, Faculty of Mathematics and Physics,
Prague , Czech Republic Czech Technical University, Faculty of Nuclear Sciences and Physical Engineering,
Prague , Czech Republic A.A. Logunov Institute for High Energy Physics of the National Research Centre “Kurchatov Institute”,
Protvino , Russia National Research Centre "Kurchatov Institute" B. P. Konstantinov Petersburg Nuclear Physics Institute, Gatchina,
St.Petersburg , Russia Kungliga Tekniska Högskolan,
Stockholm , Sweden Stockholms Universitet,
Stockholm , Sweden Sardar Vallabhbhai National Institute of Technology, Applied Physics Department,
Surat , India Veer Narmad South Gujarat University, Department of Physics,
Surat , India Florida State University,
Tallahassee , U.S.A. Università di Torino and INFN Sezione di Torino,
Torino , Italy INFN Sezione di Torino,
Torino , Italy Politecnico di Torino and INFN Sezione di Torino,
Torino , Italy Uppsala Universitet, Institutionen för fysik och astronomi,
Uppsala , Sweden National Centre for Nuclear Research,
Warsaw , Poland Österreichische Akademie der Wissenschaften, Stefan Meyer Institut für Subatomare Physik,
Wien , Austria National Research Nuclear University MEPhI (Moscow Engineering Physics Institute),
Moscow , Russia Faculty of Physics, University of Warsaw,
Warsaw , Poland Department of Physics, University of Tehran, North Karegar Avenue
Tehran , Iran Institut für Theoretische Physik, Justus-Liebig-Universität Gießen,
Gießen , Germany Institut for Advanced Simulation, Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich,
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Dublin
2, Irelandthe date of receipt and acceptance should be inserted later
Abstract
The Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, provides uniquepossibilities for a new generation of hadron-, nuclear- and atomic physics experiments. The future antiPro-ton ANnihilations at DArmstadt (PANDA or P ANDA) experiment at FAIR will offer a broad physicsprogramme, covering different aspects of the strong interaction. Understanding the latter in the non-perturbative regime remains one of the greatest challenges in contemporary physics. The antiproton-nucleoninteraction studied with PANDA provides crucial tests in this area. Furthermore, the high-intensity, low-energy domain of PANDA allows for searches for physics beyond the Standard Model, e.g. through highprecision symmetry tests. This paper takes into account a staged approach for the detector setup and forthe delivered luminosity from the accelerator. The available detector setup at the time of the delivery ofthe first antiproton beams in the HESR storage ring is referred to as the
Phase One setup. The physicsprogramme that is achievable during Phase One is outlined in this paper.
PACS.
The Standard Model (SM) of particle physics has to datesuccessfully described elementary particles and their in-teractions. However, many challenging questions are yetto be resolved. Some of these are being studied at thehigh energy frontier at e.g. the LHC at CERN. A differ-ent approach is the high precision/high intensity frontierprovided by exclusive measurements of hadronic reactionsat intermediate energies. This will be exploited in the up-coming PANDA experiment at FAIR, where antiproton-proton and antiproton-nucleus interactions serve as di-agnostic tools. The PANDA physics programme consistsof four main physics domains: a) Nucleon structure b)Strangeness physics c) Charm and exotics and d) Hadronsin nuclei, as illustrated in Fig. 1. The theory describing the strongly interacting quarks andgluons is Quantum Chromodynamics (QCD) [1]. At highenergies, or short distances, the strong coupling α s issufficiently weak to enable a perturbative treatment i.e. pQCD. Quarks act as free particles due to asymptoticfreedom , an inherent property of QCD [2], and the predic-tions from pQCD have been rigorously and successfullytested in experiments [3]. At low and intermediate ener-gies, α s increases and pQCD breaks down. The stronglyinteracting quarks and gluons are confined into hadrons within a radius of ≈ ഥ𝒑𝒑 and ഥ𝒑𝑨 interactions Fundamental Question PANDA Physics Pillars
QCD in Confinement DomainFundamental symmetries
Nucleon Structure
Strangeness PhysicsCharm and Exotics
Hadrons in Nuclei
Figure 1: The PANDA physics domains emerging when using antiproton interactions with nucleons and nuclei as diagnostictools to shed light on some of the most challenging unresolved problems of contemporary physics. controversial, the mass [6] remain objects of intense dis-cussions and research. Understanding the former requiresdetailed knowledge about the distribution and motion ofthe quarks and gluons inside the hadrons. These can bequantified by e.g. electromagnetic structure observablessuch as form factors and parton distributions.The mass of a purely light-quark system such as thenucleon, is to a very large extent generated dynamically bythe strong interaction via the QCD intrinsically generatedscale Λ QCD (the scale at which non-perturbative effectsbecome dominant), rather than the Higgs mechanism. Na-ture is close to the chiral-limit case of massless up anddown quarks. Explaining the mass of nucleons and otherhadrons requires a detailed theoretical understanding ofthe low-energy aspects of QCD, which goes hand in handwith the experimental determination of the hadronic exci-tation spectrum. In particular, it is illuminating to studyhadrons whose building blocks have different masses, fromthe massless gluons on one hand, to heavy quarks, e.g. charm, on the other. In the latter case the charm quark(s)can be viewed as a near static color source(s) surroundedby the strongly interacting light quarks, a scenario thatleads to additional, new forms of matter.
Glueballs , suggested by theorists since more than 40years [7], constitute one extreme since they consist solelyof massless gluons. Hence, 100% of the glueball mass isdynamically generated by the strong interaction. However,unambiguous evidence for their existence has not yet beenfound. This scenario also holds for hybrids [8], consistingof massive quarks and massless gluons.The other extreme are "pure" quark systems contain-ing heavier quarks, e.g. strange or charm. The experi-mentally well-established hyperons are baryons just likethe nucleons, but contain one or several heavier quarks.Strange systems provide a bridge between nucleons,composed of essentially relativistic and non-perturbative quarks, on one side, and the fairly non-relativistic systemscontaining heavy charm or beauty quarks on the other.The strong coupling at the charm scale is α s ≈ c ¯ c )show interesting features; in particular the XYZ statesthat do not fit into the conventional quark-antiquark pic-ture but must have a more complicated structure [9–11].Even for the conventional nucleon, the existence of non-perturbative intrinsic charm, a first-principle property ofQCD, has been proposed [12–14], but experimentally notfirmly confirmed.At the next level of complexity, where nucleons formnuclei, a long-standing question is how the nuclear forceemerges from QCD. The short-distance structure of nu-clei, studied in hadronic interactions with atomic nuclei,can shed light on this issue. At high energies, the stronginteraction is predicted to be reduced due to colour trans-parency [16]. At low energies, hadrons are implanted inthe nuclear environment and form bound systems withfinite life-time. Those could be hypernuclei where one(or several) nucleon(s) in a nucleus is replaced by a hy-peron. Studies of hypernuclei could shed light on the long-standing hyperon puzzle of neutron stars. Here, hyperon-nucleon and hyperon-hyperon interactions give rise to hy-peron pairing which can suppress the cooling of neutronstars [17].Finally, the validity and limitations of the SM itself re-main an open question at the most fundamental level. Oneexample is the matter-antimatter asymmetry, or baryonasymmetry, of the Universe, that cannot be explainedwithin the SM. Unless fine-tuned in the Big Bang, thebaryon asymmetry should be of dynamical origin, referredto as baryogenesis [19]. This would however require e.g.
CP violating processes to an extent that so far have notbeen observed experimentally.To summarise, despite the many successes of theSM, many unresolved puzzles remain. Various effortsfrom both, theoretical and experimental frontiers are inprogress or planned in the near future to address thesepuzzles [18]. In this paper, we highlight PANDA, a futurefacility that will exploit the annihilation of antiprotonswith protons and nuclei to shed light on the mysteries be-hind the fundamental forces in nature. PANDA has theunique capability to make discoveries and to carry outprecision studies in the field of particle, hadron, and nu-clear physics. In this paper, we outline the PANDA physicsobjectives with emphasis on the programme foreseen forthe first phase of operation of PANDA, in the followingreferred to as
Phase One . The structure of the paper isas follows. First, we elaborate on the advantages of an-tiprotons as a probe. Next, we give a detailed presenta-tion of the PANDA experiment in general and the PhaseOne conditions in particular. We go through each one ofthe PANDA physics sections and discuss their underlyingpurpose and aims, the present experimental status andthe potential for PANDA Phase One. Finally, we con-clude each part by providing a discussion on its impactand long-term perspectives in which we also briefly out-line additional follow-up aspects for the subsequent phasesof PANDA.
The intense and precise antiproton beam foreseen inPANDA has many advantages: – The cross sections of hadronic interactions are gener-ally large. – Individual meson-like states can be produced in for-mation without severe limitations in spin and paritycombinations. – Baryons with various flavour, spin and parity can beproduced in two-body reactions. – The annihilation process could proceed via gluons and,in that case, providing a gluon-rich environment.In the following, we elaborate on these points in moredetail.The cross sections associated with antiproton-protonannihilations are generally several orders of magnitudelarger than those of experiments using electromagneticprobes. This enables excellent statistical precision alreadyat the moderate luminosities available in Phase One. Inparticular, hadrons composed of strange quarks and glu-ons are abundantly produced as demonstrated at a multi-tude of previous experiments at LEAR, CERN [20].Hadronic reactions can be divided into two classes: for-mation and production . In formation, the initial systemsfuse into one single state. The line shape of such a statecan be determined from the initial system, using a tech-nique called resonance energy scan . The beam momentumis changed in small steps thereby varying the centre-of-mass energy in the mass region of the state of interest and the production rate is measured. Each resulting datapoint is a convolution of the beam profile and the reso-nance cross section according to Fig. 2. The true energy-dependent cross section (green dashed line) is determinedby the effectively measured cross section (solid blue line)based on the measured yields (markers) and the beam mo-mentum spread (red dotted line).The smaller the momentum spread of the beam, themore precise the measurement of the resonant line shapewill be. In formation, the possible quantum numbers ofthe formed state depend on the probes. In e + e − annihi-lations, processes in which the formed state has the samequantum numbers as the photon, i.e. J P C = 1 −− , arestrongly favoured. States with any other quantum num-ber are strongly suppressed and these therefore have tobe produced together with a system of recoiling particles, i.e. in production , or from decays of the −− state. Thedisadvantage of production with recoils is that the stateof interest needs to be identified by the decay products.As a consequence, the mass resolution is limited by thedetector resolution, which is typically several orders ofmagnitude worse than the beam momentum spread. Inantiproton-proton annihilations, any state with ¯ qq -like, ornon-exotic, quantum numbers can be created in formation.With a cooled antiproton beam, like the one foreseen forPANDA, the centre-of-mass energy resolution is excellent.Experiments of this kind are therefore uniquely suitedfor precision studies of masses, widths and line-shapes ofmeson-like states with non-exotic quantum numbers thatare different from −− . A prominent example of this isthe hidden-charm χ c (3872) with J P C = 1 ++ , that wewill discuss further in Section 6.2.2. Furthermore, PANDAis unique in its capability to probe resonances with highspin. These are difficult to produce using electromagneticprobes, as well as in decays of e.g. B mesons.Baryons and antibaryons can be produced in two-body reactions ¯ pp → ¯ B B . The final state baryons cancarry strangeness or charm provided the ¯ B B systemis flavour neutral. In particular for multi-strange hyper-ons, this is an advantage compared to meson or photonprobes, where strangeness conservation requires that thehyperon is produced with the corresponding number ofassociated kaons. As a result, the final state comprises atleast three pseudo-stable particles, which complicates thepartial-wave analysis necessary in hyperon spectroscopy.Two-body reactions on the other hand, in particular closeto the kinematic threshold, typically involve few partialwaves. Furthermore, spin observables and decay param-eters can be accessed in a straight-forward way in two-body reactions. This enables production dynamics stud-ies as well as charge conjugation parity (CP) symmetrytests in the strange sector. The particle-antiparticle sym-metric final state minimises systematic uncertainties. Inprinciple, the aforementioned advantages apply also forbaryon-antibaryon production in e + e − colliders. However,the typically much smaller cross sections result in low pro-duction rates. The resulting data samples are therefore This state is also known as the X (3872) . In this paper, weuse the notation used by the Particle Data Group. E CM Beam profileMeasured Rate
Resonance Cross Section
Figure 2: Schematics of a resonance energy scan: The true energy dependent cross-section (dashed green line), the beammomentum spread (dashed red line), the measured yields (black markers), and the effectively measured energy dependent eventrate (solid blue line) are illustrated. smaller and in order to obtain sufficiently many events,methods such as missing kinematics or single-tag analysisis common. This however limits the possibility to reducethe background and achieve good resolution. In ¯ pp experi-ments, one can obtain large data samples also in exclusiveanalysis, which increases the discovery potential.The ¯ pp → X process includes quark-antiquark anni-hilations, which result in gluons. Therefore, antiproton-proton annihilation provides a gluon-rich environment,where states with a gluonic component are likely to beproduced if they exist. Gluon-rich environments exist alsoin radiative decays of charmonia and in central hadron-hadron collisions. However, in radiative decays, recon-struction of the properties of the resonant state of in-terest relies solely on detector information since the pro-cess is not a formation process. As a result, the resolutionis limited by the detector. The same is true for centralhadron-hadron collisions, where the final state consists ofthe scattered hadrons and the produced resonance. Thespin and parity of the resulting multi-particle final stateis complicated to reconstruct without assumptions aboutthe underlying production mechanism. This in turn leadsto model-dependent ambiguities. The process ¯ pp → X ,where X refers to a single resonance, is less complicatedin this regard.The momentum range, precision and intensity of theantiproton beam in PANDA is tailored for strong interac-tion studies. PANDA will give access to the mass regime whereby recently new and interesting forms of hadronicmatter have been observed ( XY Z states), it can studythe hadron-antihadron formation close to their produc-tion threshold, and it has the resolution to measure theline-shape of states very accurately.
The PANDA experiment is one of the four pillars ofFAIR [21]. PANDA will be a fixed-target experimentwhere the antiproton beam will impinge on a cluster jetor pellet target ( ¯ pp ) or target foils ( ¯ pA ). The High En-ergy Storage Ring (HESR) [22] can provide antiprotonswith momenta from 1.5 GeV/ c up to 15 GeV/ c . Thephysics goals of PANDA outlined in this paper requirea detector system with nearly full solid-angle coverage,high-resolution tracking, calorimetry and particle identi-fication over a broad momentum range as well as vertexreconstruction.The success of the physics programme will depend notonly on the detector performance but also on the qualityand intensity of the antiproton beam. Antiprotons are pro-duced from reactions of 30 GeV/ c protons on a nickel orcopper target. The source of these protons will be a ded-icated high-power proton Linac followed by the existingSIS18 synchrotron and the new SIS100 synchrotron. Pro-duced antiprotons are focused by a pulsed magnetic horn and selected in a magnetic channel at a momentum ofaround 3.7 GeV/ c . After phase-space cooling in the Col-lector Ring (CR), packets of about antiprotons aretransferred to the HESR for accumulation and subsequentacceleration or deceleration necessary for measurementsin PANDA. In this mode of operation, the HESR is ableto accumulate up to antiprotons from 100 injectionswithin a time span of 1000 s. In a later stage of FAIR, theaccumulation will take place in a dedicated ring, i.e. theRecuperated Experimental Storage Ring (RESR), allow-ing for up to antiprotons to be injected and storedin the HESR. An important feature of the HESR is theversatile stochastic cooling system operating during accu-mulation and target operation. It is designed to delivera relative beam-momentum spread ( ∆p/p ) of better than · − . Furthermore, it includes a barrier bucket cavitythat compensates for the mean energy loss in the thicktarget and that fine-tunes the absolute beam energy. Thisenables precise energy scans around hadronic resonancesand kinematic thresholds. The centre-of-mass resolutionwill be about 50 keV, which to date is unreachable byother accelerators using different probes. The PANDA experiment will follow a staged approach inthe construction of the detector and in the usage of theantiproton beam. It comprises four phases, briefly outlinedbelow.The first phase,
Phase Zero , started in 2018 and itrefers to physics activities where PANDA detectors andanalysis methods are used at existing and running facili-ties. One example is the usage of PANDA tracking stationsin the upgraded HADES at GSI [23], another is the deploy-ment of parts of the PANDA calorimeter for experimentswith A1 at MAMI [24].The installation of the first major detector componentsof PANDA, including the two spectrometer magnets, willfollow Phase Zero. This installation phase will be com-pleted with a commissioning of the detectors using a pro-ton beam at the HESR. The start of
Phase One will bemarked with the usage of antiprotons together with thecommissioned detectors. The corresponding physics pro-gramme is outlined in this paper. During Phase One, theHESR will be capable of accumulating at most 10 an-tiprotons in 1000 s. The luminosity is expected to risegradually from about cm − s − to the maximum of × cm − s − (at 15 GeV/ c ) during Phase One. Theavailable PANDA detector of Phase One will be referredto as the start setup and includes most of the major com-ponents as shown in Fig. 3. A description of the variousavailable detector components will be given in section 3.2.The total integrated luminosity for Phase One is expectedto be about 0.5 fb − .The detector will be completed according to the finaldesign in Phase Two . The main components beyond thestart setup are the detector for charged particle identifi-cation in the forward region and the completion of the GEM and forward trackers. Moreover, a pellet target sys-tem will become available. The corresponding setup willbe referred to as the full setup . In
Phase Three , the RESRwill be available at FAIR which provides an increase inluminosity at HESR by a factor of approximately 20.
To achieve the full physics potential of PANDA, the com-plete set of detector systems is needed. In Phase One, notall of these will be available and the focus is thereforeon reactions with large expected cross sections and goodsignal-to-background ratios as well as relatively small mul-tiplicities of final-state particles.In this section, we primarily describe the hardware sys-tems to be installed as part of the start setup . The PANDAdetector consists of two main parts: – The
Target Spectrometer (TS) for the detection of par-ticles at large scattering angles (> 10 ◦ ). The momen-tum measurement of charged particles is based on asuperconducting solenoid magnet with a field strengthof 2 T. – The
Forward Spectrometer (FS) for particles emittedin the forward direction ( < ◦ in the horizontal di-rection and from < ◦ in the vertical direction). Themomentum measurement is based on a dipole magnetwith a bending power of up to 2 Tm.The magnet system is described in Ref. [25]. Both spec-trometers are integrated with devices to perform taskssuch as high resolution tracking, particle identification(PID), calorimetry and muon detection.The internal target operation of PANDA will employa cluster jet target that can be operated with hydrogen aswell as heavier gases. With hydrogen, an average luminos-ity of cm − s − can be reached in the experiment [26]. The beam-target interaction point will be enclosed by theMicro Vertex Detector (MVD) that will measure the in-teraction vertex position. It will consist of hybrid siliconpixels and silicon strip sensors. The vertex resolution isdesigned to be about 35 µ m in the transverse directionand 100 µ m in the longitudinal direction. Moreover, theMVD significantly contributes to the reconstruction of thetransverse momentum of charged tracks [27]. The StrawTube Tracker (STT) will surround the MVD with theprimary purpose of measuring the momenta of particlesfrom the curvature of their trajectories in the solenoidfield. The low-mass (1.2% X ) STT detector will con-sist of gas-filled straw-tubes arranged in cylindrical lay-ers parallel to the beam direction. From these straws, aresolution better than 150 µ m in the transverse x and y coordinates can be achieved. Some straw tube layerswill be skewed with respect to the beam direction whichenables an estimation of the z coordinate along to thebeam. The z resolution will be approximately 3 mm. The Straw Tube TrackerMicro Vertex Detector Forward Tracking System Luminosity MonitorBarrel TOF Muon DetectorsBarrel DIRC Forward TOF Muon Range SystemForward Shashlyk EMCPWO EMC GEM Detector
Figure 3: Schematic overview of the start setup of PANDA. The various tracking detectors are indicated in red, the componentsfor particle identification in blue, and the electromagnetic calorimeters in green.
STT will also contribute to the charged particle identi-fication by measuring the energy loss dE/dx . Details ofthe STT can be found in Ref. [28]. The PANDA BarrelDIRC [29], surrounding the STT, will cover the polar an-gle region between 22 ◦ and 140 ◦ . The DIRC will be sur-rounded by a barrel-shaped Time of Flight (TOF) detec-tor consisting of scintillating tiles read out by silicon pho-tomultipliers. The expected time resolution, better than100 ps, will allow for precision timing of tracks for eventbuilding and fast software triggers [30]. The electromag-netic calorimeter (EMC), that will measure the energiesof charged and neutral particles, will consist of three mainparts: The barrel, the forward endcap and the backwardendcap. The expected high count rates and the geomet-rically compact design of the target spectrometer requirea fast scintillator material with a short radiation lengthand small Molière radius. Lead-tungstate (PbWO ) ful-fils the demands for photons, electrons and hadrons inthe energy range of PANDA. The signals from the lead-tungstate crystals are read out by large-area avalanchephotodiodes, except in the central part of the forwardendcap where vacuum photo-tetrodes are needed for theexpected higher rates. The EMC also plays an importantrole in the particle identification. In particular for elec-tron/positron identification, it can suppress background from charged pions with a factor of about 1000 for mo-menta above 0.5 GeV/ c . A detailed description of the de-tector system can be found in Ref. [31]. The laminatedyoke of the solenoid magnet, outside the barrel EMC, isinterleaved with sensitive layers to act as a range systemfor the detection and identification of muons. Rectangu-lar aluminium Mini Drift Tubes (MDT) are foreseen assensors between the absorber layers. Details of this sys-tem are described in Ref. [32]. Downstream of the target,within the TS, a system of Gas Electron Multiplier (GEM)foils will be located. The GEM planes will offer trackingof particles emitted with polar angles below 22 ◦ , a regionthat the STT in the target spectrometer will not cover. Inthe start setup, two GEM stations will be installed. Partof the particles that pass the GEM tracking detector willbe further registered by the Forward Spectrometer (FS)rather than the TS. The FS detector systems are conceptually similar to thoseof the TS, but will have a planar geometry instead of acylindrical. The detector planes will be arranged perpen-dicular to the beam pipe and thereby measure the de-flection of particle trajectories in the field of the dipole magnet. Downstream of the GEMs, two pairs of strawtube tracking stations are foreseen for the start setup [33].One will be placed in front of the dipole magnet and theother inside its field. Particle identification will be pro-vided by the Forward TOF wall consisting of scintillat-ing slabs. The signals from the latter will be read outby photomultiplier tubes offering a time resolution betterthan 100 ps [34]. Forward-going photons and electrons willbe detected and identified by a Shashlyk-type calorimeterwith high resolution and efficiency. The detection is basedon lead-scintillator sandwiches read out with wave-lengthshifting fibres passing through the block and coupled tophotomultiplier tubes. The system is described in detailin Ref. [35]. At the end of the FS, a muon range systemis placed using sensors interleaved with absorber layerssimilar to the TS.
The luminosity at PANDA will be determined by usingelastic antiproton-proton scattering as the reference chan-nel. Since the Coulomb part of the elastic scattering canbe calculated precisely and dominates at small momen-tum transfers, the polar angle of 3-8 mrad is chosen forthe measurement. The track of each scattered antiprotonand therefore the angular distribution of the tracks will bemeasured by the luminosity detector made of four layersof thin monolithic silicon pixel sensors (HV-MAPS) [36].An absolute precision of 5% for the time integrated lumi-nosity is expected and a relative precision of 1% duringthe energy scans.
The PANDA data acquisition concept is being developedto match the complexity of a next-generation hadronphysics experiment. It will make use of high-level soft-ware algorithms for the on-line selection of events withinthe continuous data stream. This so-called software-basedtrigger system replaces the more traditional hardware-driven trigger systems that have been a common standardin the past. In order to handle the expected Phase Oneevent rate of MHz, every subdetector system is a self-triggering entity. Signals are detected autonomously bythe sub-systems and are pre-processed in order to trans-mit only the physically relevant information. The onlineevent selection occurs in computing nodes, which first per-form event-building followed by filtering of physical signa-tures of interest for the corresponding beam-target set-tings. This concept provides a high degree of flexibilityin the choice of trigger algorithms and hence a more so-phisticated event selection based on complex trigger con-ditions, compared to the standard approach of hardware-based triggers.
The feasibility studies presented in this paper have beencarried out using a common simulation and analysis framework named
PandaROOT [37]. This framework pro-vides a complete simulation chain starting from the MonteCarlo event generation, followed by particle propagationand detector response, signal digitisation, reconstructionand calibration, and finally the physics analysis.PandaROOT is derived from the FairROOT frame-work [38] which is based on ROOT [39]. FairROOT offersa large set of base classes which enables a straight-forwardcustomisation for each individual detector setup. It of-fers an input-output manager, a run manager, databasehandling, an event display and the Virtual Monte Carlo(VMC) interface which allows to select different simula-tion engines. In addition, it uses the task system of ROOTto combine and exchange different algorithms into a sim-ulation chain.The first part in the simulation chain is the eventgeneration. Here, the initial interaction of the antipro-ton beam with the target material is simulated using aMonte Carlo approach. Different generators exist for dif-ferent purposes. Dedicated reactions and their subsequentdecays are generated by the standard signal generator
Evt-Gen [40]. For the generic background, the
Dual PartonModel (DPM) [41] and the
Fritiof (FTF) model [42] can bechosen. Both include all possible final states and are tunedto an exhaustive compilation of experimental data. Fordetector- and software performance studies, the
BoxGen-erator creates single types of particles within user-definedmomentum and angular ranges.The generated particles are propagated through a de-tailed detector model, simulating the reactions with thedetector material and possible decays in-flight. For thispurpose, Geant3 and Geant4 are available to the user.The level of detail in the virtual detector description variesbetween the different subdetectors but all active compo-nents, as well as most of the passive material, are included.Separate descriptions are prepared for the start setup andthe full setup. From this stage, the energy deposit, theposition and the time of a given interaction in a sensi-tive detector element is delivered as output, all with infi-nite resolution. Real data will however consist of electronicsignals with finite spatial- and time resolution. Therefore,the digitisation converts the information from the parti-cle propagation stage into signals that mimic those of areal experiment. This includes noise and effects from dis-criminators and electronics. For some detector systems,the final electronics is not yet defined. In those cases, thedigitisation procedure is based on realistic assumptions.In the reconstruction, the signals from the digitisationstage are combined into tracks. The procedure is dividedinto two steps: a local and a global part. In the local part,detector signals in a given tracking subdetector are com-bined into tracklets. Furthermore, the signal informationis converted back to physical quantities such as position,energy deposit and time. In the global reconstruction, thetracklets from different tracking detectors are combinedinto tracks. Different algorithms are applied in the barrelpart and the forward part. The track finding is followedby track fitting using a Kalman filter, where effects fromdifferent particle species and materials are taken into ac- count. PANDA simulations thereby achieve a momentumresolution of about 1%.At the particle identification stage, the informationfrom the dedicated PID detectors and the EMCs are asso-ciated with a charged track based on the distance betweenthe predicted flight path and the hit position in the de-tector. Hits in the EMC without a corresponding chargedtrack are regarded as neutral particles. The probabilitiesfor various particle types of the different subdetectors arethen combined into an overall probability of a given par-ticle species.The selection of events for partial or complete reactionchannels, referred to as Physics Analysis , is performedbased on the combined tracking, PID and calorimetrydata using the Rho package, an integrated part of Panda-ROOT. With Rho, various constrained fits such as vertexfits, mass fits and tree fits are available.
Hadron structure observables provide a way to test QCDand phenomenological approaches to the strong interac-tion in the confinement domain. Electromagnetic probesare particularly convenient and have been used extensivelyover the past 60 years. The structure is parameterised interms of observables like form factors or structure func-tions .Electromagnetic form factors (EMFFs) quantify thehadron structure as a function of the four-momentumtransfer squared q . At low energies, they probe distancesof about the size of a hadron. EMFFs are defined on thewhole q complex plane and for q < , they are referredto as space-like and for q > as time-like . Space-likeEMFFs are real functions of q and can be studied inelastic electron-hadron scattering. Assuming one-photonexchange (OPE) being the dominant process, protons andother spin-1/2 particles are described by two EMFFs: theelectric G E ( q ) and the magnetic G M ( q ) form factor.In the so-called Breit frame , these are the Fourier trans-forms of the charge and magnetisation density, respec-tively. Time-like EMFFs are complex and can be stud-ied using different processes in different q regions. In thefollowing, we consider baryons, denoted B , B and B .For unstable baryons, the low- q ( q < ( M B − M B ) )part of the time-like region is probed by Dalitz decays, i.e. B → B (cid:96) + (cid:96) − . For the proton, the so-called unphys-ical region ( m l < q < ( M B + M B ) = 4 M p with m l the mass of the lepton l ) can be probed by the reaction ¯ pp → (cid:96) + (cid:96) − π . For all types of baryons, the high- q region( q > ( M B + M B ) ) can be accessed by B ¯ B ↔ e + e − . If B = B = B , then the form factors are direct , whereasif B (cid:54) = B , transition form factors are obtained. Beinganalytic functions of q , space-like and time-like form fac-tors are related by dispersion theory. The processes forstudying EMFFs at different q are summarised in Fig. 4.At high energies, corresponding to distances muchsmaller than the size of a hadron, individual buildingblocks are resolved rather than the hadron as a whole. Here, the factorisation theorem applies, stating that theinteraction can be factorised into a hard, reaction-specificbut perturbative and hence calculable part and a soft,reaction-universal and measurable part. In the space-likeregion, probed by deep inelastic lepton-hadron scatter-ing, the structure is described by parton distributionfunctions (PDFs) [43], generalised parton distributions(GPDs) [44–50] and transverse momentum dependent par-ton distribution functions (TMDs) [51]. In the time-likeregion, the corresponding observables are generalised dis-tribution amplitudes (GDAs) [52] and transition distribu-tion amplitudes (TDAs) [53–55,98]. These can be accessedexperimentally in hard hadron-antihadron annihilationswith the subsequent inclusive production of a real or avirtual photon. In the following, we focus on EMFFs, inline with the emphasis of Phase One. Elastic electron-proton scattering has been studied sincethe 1960s [56]. During the first decades, unpolarisedelectron-nucleon scattering was analysed using the Rosen-bluth separation method [57]. Modern facilities, offeringhigh-intensity lepton beams and high-resolution detec-tors, gave rise to a renewed interest in the field [58, 59].In particular, the polarisation transfer method [60] ap-plied by the JLab-GEp collaboration (see [59] and refer-ences therein) revealed the surprising result that the ratio µ p G E /G M , where µ p denotes the proton magnetic mo-ment, decreases almost linearly with Q = − q . This re-sult is in contrast to the previous measurements of unpo-larised elastic ep scattering and it has been suggested tobe due to the involvement of two-photon exchange (TPE)[61]. The large amount of high-quality data inspired ex-tensive activity also on the theory side, from which wehave learned about the importance of vector dominanceat low q [62, 63].Until recently, measurements in the time-like regionhave not achieved precisions comparable to the corre-sponding space-like data, partly because most e + e − col-liders have been optimised in different q regions [64, 65].In ¯ pp annihilation experiments, the clean identification of e + e − pairs has been a challenge. Among the few experi-ments that so far have provided a separation between G E and G M of the proton, the results at overlapping energiesdisagree. The ratio R = | G E | / | G M | , accessible from thefinal state angular distribution, has been measured below q = 9 (GeV/ c ) by PS170 at LEAR [66], BABAR [67]and more recently by BESIII [68] and CMD-3 [69]. ThePS170 and BABAR data differ up to 3 σ , while the BE-SIII and CMD-3 measurements have large total uncer-tainties. In the limit | q | → ∞ , the space-like and thetime-like form factors should approach the same value asa consequence of the Phragmén-Lindelöf theorem [70]. Ex-perimentally, the onset of this scale has not been estab-lished (see Ref. [65] for a recent review). In measurementsjust below | q | = 20 . (GeV/ c ) , the time-like magneticform factor is about two times larger than the correspond-ing space-like one. A recent analysis of BaBar data above -Q = q < 0 q = 0 q = (m B1 –m B2 ) q = (m B1 +m B2 ) q Unphysical region ҧ𝑝𝑝 → 𝑒 + 𝑒 − 𝜋 Low- q 𝐵 → 𝐵 𝑒 + 𝑒 − 𝐵 → 𝐵 𝛾 Space-like 𝑒 − 𝐵 → 𝑒 − 𝐵 𝑒 − 𝑒 + High- q 𝑒 + 𝑒 − → 𝐵 ത𝐵 ത𝐵𝐵 → 𝑒 + 𝑒 − 𝐵 𝐵 𝑒 + 𝑒 − π ҧ𝑝 ҧ𝑝𝑝 𝑒 − 𝑒 + 𝐵ത𝐵 𝑒 − 𝑒 − 𝐵 𝐵
Figure 4: Processes for extracting EMFF in the space-like (left) and time-like (right) region. The low- q ( q < ( M B − M B ) )part of the time-like region is studied by Dalitz decays, the unphysical region ( m e < q < ( M B + M B ) ) by ¯ pp → (cid:96) + (cid:96) − π and the high- q region ( q > ( M B + M B ) ) by B ¯ B ↔ e + e − . | q | = 20 . (GeV/ c ) , indicates a decreasing difference,but the uncertainties are large [67].In 2019, the BESIII collaboration measured the Borncross section of the process e + e − → ¯ pp and the protonEMFFs at 22 centre-of-mass energy points from q = 4 (GeV/ c ) to q = 9 . (GeV/ c ) with an improved accu-racy [71], comparable to data in the space-like region. Un-certainties on the form factor ratio | G E | / | G M | better than have been achieved at different q values below (GeV/ c ) . The BESIII data on the proton effective formfactor confirm the structures seen by the BABAR Col-laboration. These structures are currently the subject ofseveral theoretical studies [72–74].The PANDA experiment aims to improve the currentsituation of the time-like EMFFs by providing data in alarge kinematic region between . (GeV/ c ) and ∼ (GeV/ c ) . Precisions in this region of at least a factor 3better than the current data, as well as measurements inthe unphysical region below (2 M p ) , whereby M p is themass of the proton, are called for to constrain the theo-retical models and to resolve the aforementioned issues. The PANDA experiment in Phase One offers the oppor-tunity to measure the proton form factor in the process ¯ pp → (cid:96) + (cid:96) − , ( (cid:96) = e, µ ) over a wide energy range, in-cluding the high q region [75, 76]. The ¯ pp → µ + µ − re-actions can be studied for the first time. The interest for ¯ pp annihilation into heavy leptons ( µ and τ ) has been discussed in several theory studies [77–79]. A prominentexample is the proton radius puzzle. Previous measure-ments revealed a significant discrepancy between electronand muon data [80]. However, recent measurements showbetter agreement [81] and the issue may be close to be-ing resolved [82]. Nevertheless, our planned form factormeasurements with PANDA provide an independent crosscheck of the electron-muon universality.Furthermore, the unphysical region of the protonEMFFs can be accessed through the measurement of the ¯ pp → (cid:96) + (cid:96) − π process [83–85]. These measurements byPANDA are unique and will provide the possibility to testmodels for this process that contain EMFFs [86]. ¯ pp → e + e − A previous simulation study of the process ¯ pp → e + e − within the PandaROOT framework demonstrates the ex-cellent prospect of nucleon structure studies with thePANDA design luminosity [75]. The simulations were per-formed applying an integrated luminosity of 2 fb − foreach energy-scan point and the full PANDA setup. A new,dedicated simulation study with the Phase One condi-tions has recently been performed at q = 5 . and . (GeV/ c ) ( p lab = 1 . and 3.3 GeV/ c , respectively). Thedifficulty of the measurement is related to the hadronicbackground, mostly annihilation with the subsequent pro-duction of two charged pions. This reaction has a cross sec-tion about five to six orders of magnitude larger than thatof the production of a lepton pair. In the energy scale of the PANDA experiment, the mass of the electron is suf-ficiently close to the pion mass for this to be an issue.Therefore, the signal and the main background reactionshave very similar kinematics. The signal events are gen-erated according to the differential cross section param-eterised in terms of proton EMFFs from Ref. [87] withthe hypothesis that R = | G E | / | G M | = 1 . The same eventselection criteria as in Ref. [75] were applied. The out-put of the PID and tracking subdetectors as EMC, STT,MVD, and barrel DIRC have been used to separate thesignal from the background. These resulted in signal ef-ficiencies of 40% at p lab = 1.5 GeV/ c and 44% at p lab = 3.3 GeV/ c . The suppression factor of the main back-ground process ¯ pp → π + π − was found to be of the order ∼ . The proton form factors | G E | , | G M | , and their ratio R = | G E | / | G M | are extracted from the electron angulardistribution, after reconstruction and efficiency correction.The proton effective form factor | G e eff | is extracted fromthe determined cross section of the signal ( σ ) integratedover the electron polar angle. The resulting precision fordifferent q are summarised in Table 1 and shown in Fig. 5,together with existing experimental data. Systematic un-certainties arise due background contamination and un-certainties in the luminosity measurement. These effectscan be quantified by MC simulations. From these we con-clude that the proton EMFFs can be measured with anoverall good precision and accuracy. At low q , the sig-nal event yield is relatively large. However, at higher q ,the cross section of the process reduces significantly whichleads to a smaller event yield and thus larger statisticaluncertainties for a given integrated luminosity. Previousstudies show that the efficiency at larger q is sufficientfor precise cross section measurements [75]. ¯ pp → µ + µ − An independent Monte Carlo simulation study of the ¯ pp → µ + µ − reaction has been carried out at q = 5 . (GeV/ c ) . The di-muon channel provides a clean environ-ment, where radiative corrections from final state pho-ton emissions are reduced thanks to the larger mass ofthe muon. However in case of muons, the suppression ofthe hadronic background ¯ pp → π + π − is more challenging.Muon identification is mainly based on the informationfrom the Muon System, since other subdetectors show lessseparation power which complicates the background sep-aration considerably. Monte Carlo samples of eventswere generated for the background process ¯ pp → π + π − .They were used for the determination of the backgroundsuppression factor and for the calculation of the pion con-tamination, which will remain in the signal events afterthe application of all selection criteria. The separationof the signal from the background has been optimisedthrough the use of multivariate classification methods(Boosted Decision Trees). The event selection is describedin Ref. [76]. A background rejection factor of . × − was achieved, resulting in a signal-to-background ratio of1:8. The total signal efficiency is . . Due to the insuffi-cient background rejection, the pion contamination needs to be subtracted from the signal and the corresponding an-gular distributions by Monte Carlo modelling and subse-quent subtraction. This has been taken into account in ourfeasibility studies. The angular distributions from the pioncontamination are reconstructed with both the expectedmagnitude and shape. The sensitivity of the EMFFs tothe shape was investigated and from that, the systematicuncertainty was estimated. The ratio R , and consequently | G E | and | G M | , were extracted from the angular distribu-tion of the muons after background subtraction and ef-ficiency correction. The results are summarised in Fig. 5and Table 1. The uncertainty of the signal cross section isdominated by the luminosity uncertainty. The simultane-ous but independent measurement of the effective EMFFs G e eff and G µ eff from the e + e − final state and the µ + µ − final state, respectively, enable a test of the lepton univer-sality. The expected uncertainty in the ratio G e eff /G µ eff isestimated to be 3.2% already during Phase One, which issmall compared to what can be achieved at other facilities.It should be noted that although the uncertainties fromradiative corrections are not yet taken into account, theseare expected to contribute with only a small fraction tothe total uncertainty. ¯ pp → e + e − π Some information about the unphysical region can be ob-tained from the ¯ pp → e + e − π process, when studied indifferent intervals of the pion angular distribution. In thetime-like region, the EMFFs are complex, hence they havea relative phase. This phase is generally inaccessible forprotons in an experiment with an unpolarised beam ortarget. However, the cross section of ¯ pp → e + e − π channelcan provide some information, as outlined in Refs. [83,85].The validity of the theoretical models used to describethe cross section of the process ¯ pp → e + e − π needs tobe tested experimentally. Since PANDA has almost π coverage, the measurement of the final state angular dis-tributions in the processes ¯ pp → e + e − π and ¯ pp → γπ will provide a sensitive check of these models. The EMFFsextracted at threshold via ¯ pp → e + e − π and ¯ pp → e + e − or e + e − → ¯ pp can be compared and used as an additionaltest. We note that the process γp → pe + e − may give ac-cess to the EMFFs of the proton in the unphysical regionas well. Corresponding theoretical studies [99, 100], how-ever, suggest challenging measurements and the feasibilityhas not been demonstrated.For an ideal detector ( acceptance and efficiency)and an integrated luminosity of 0.1 fb − , the expectedcount rate for this reaction for q < (GeV/ c ) hasbeen found to be up to events in different intervalsof the pion angular distribution [86, 98]. This number isabout a factor two larger than the corresponding valuefor ¯ pp → e + e − at q = 5 . (GeV/ c ) . The large ex-pected count rate of ¯ pp → e + e − π and the clean separa-tion between this channel and background [86], indicategood prospects for EMFF measurements in the unphysi-cal region already in PANDA Phase One. Full simulation ¯ pp → e + e − and ¯ pp → µ + µ − . q / (GeV /c ) Reaction L / fb − σ σ (%) σ R (%) σ G E (%) σ G M (%)5.08 pp → e + e − pp → e + e − pp → µ + µ − ] [(GeV/c) q R - e + MC study e
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BaBarPS170 CMD-3BESIII2015BESIII2019BESIII(ISR) (a) ] [(GeV/c) q | e ff | G BaBar E835FenicePS170E760DM1DM2BESCLEOBESIII2015ADONE73CMD-3BESIII (ISR)BESIII2019 - e + MC study e
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PANDA (b) ] [(GeV/c) q | E | G - e + MC study e
PANDA - m + m MC study
PANDA
BESIII2019 (c) ] [(GeV/c) q | M | G - e + MC study e
PANDA - m + m MC study
PANDA
BESIII2019PS170BESIIIBaBar (d)Figure 5: Expected total precisions, indicated by the red and blue error bars, on the determination of (a) the proton formfactor ratio, (b) the proton effective form factor, (c) the proton electric form factor, and (d) the proton magnetic form factor,from the present simulations for PANDA Phase One as a function of q . Also shown are data from PS170 [66], BaBar [67, 88],BESIII [68, 71, 89], CMD-3 [90], E835 [91], Fenice [92], E760 [93], DM1 [94], DM2 [95], CLEO [96], and ADONE73 [97].4 studies to investigate the possibility to extract the pro-ton EMFFs in this region at PANDA are currently beingcarried out. The simulation studies presented in the previous sectionsshow that PANDA will improve the precision of the pro-ton EMFF measurements for q > . (GeV/ c ) . Thisenables systematic comparisons of space-like and time-likeEMFFs at large | q | and hence, the onset of the conver-gence scale of the space-like and time-like form factors canbe deduced. Furthermore, the foreseen PANDA studies ofthe ¯ pp → µ + µ − are unique. Since the effects from finalstate radiation are negligible for muons, this channel pro-vides an important cross check of the ¯ pp → e + e − results.In addition, it enables tests of lepton universality. Finally,in PANDA, the unphysical region of the proton EMFF willbe accessed for the first time through the ¯ pp → e + e − π process.In general, the relative phase between the electric andthe magnetic form factor is inaccessible in unpolarisedcross section measurements. To measure the phase, eithera polarised antiproton beam and/or a polarised protontarget is required. The feasibility of implementing a trans-versely polarised proton target in the PANDA detector isunder investigation. If feasible, the PANDA experimentwill offer a first direct measurement of the relative phasebetween G E and G M . The key question in hyperon physics is “What happens ifyou replace one (or several) light quark(s) in the nucleonwith one (or several) heavier one(s)?”. Strangeness servesas a diagnostic tool for various phenomena in subatomicphysics:1. Hyperons provide a new angle to the structure andexcitations of the nucleon, since the strange quark issufficiently light to relate the knowledge about hyper-ons to nucleons and vice versa.2. Hyperon decays, where the spin is experimentally ac-cessible, provide an ideal testing ground for CP viola-tion and thereby searches for physics beyond the SMat the precision frontier. Furthermore, it can give cluesabout Baryogenesis [19].3. In hypernuclei, strangeness provides an additional de-gree of freedom which plays a key role in understanding e.g. neutron stars [101].4. Enhancement of strangeness in relativistic heavy-ioncollisions was one of the first proposed signals ofQuark-Gluon Plasma [102].Number 1 will be explored with PANDA Phase Onewithin the subtopics hyperon production and hyperon spec-troscopy . Number 2, i.e. hyperon decays will be studiedextensively in Phases Two and Three. However, a goodunderstanding of the production mechanism has proven crucial to decay measurements [103] and the planned hy-peron production studies within Phase One are thereforean important milestone in the search for CP violationin baryon decays. Number 3 will be investigated duringPhases Two and Three within our programme for hadronsin nuclei. Number 4 is currently studied at ALICE [104]and is not within the scope of PANDA. However, preci-sion studies of strangeness production in elementary ¯ pp reactions contribute to a more general understanding ofstrangeness production, which can be useful also in morecomplex reactions at higher energies. The same is true forthe planned studies of hyperon-antihyperon pair produc-tion in ¯ pN reactions. These will provide information onabsorption and rescattering of hyperons as well as anti-hyperons under well-defined conditions in cold nuclei. Inthis chapter, we discuss the subtopics hyperon productionand hyperon spectroscopy in the context of what can beachieved at Phase One. In section 7.1 we also discuss anti-strange hadrons in nuclei. The scale probed in a hadronic reaction is influenced bythe energy, and, therefore, by the mass of the producedquarks. The strange quark mass is m s ≈ MeV whichcorresponds to the scale where quarks and gluons formhadrons. Therefore, the relevant degrees of freedom areunclear — quarks and gluons, or hadrons? It is challeng-ing to solve QCD in this energy regime. Guidance by ex-perimental data is needed to improve the theory in prac-tice such that quantitative predictions become possible. Asan intermediate step phenomenological models are devel-oped which are constrained by experimental data. Exclu-sive hyperon-antihyperon production provides the clean-est environment for such studies. Phenomenological mod-els based on quark-gluon degrees of freedom [105], mesonexchange [106] and a combination of the two [107] havebeen developed for single-strange hyperons. The quark-gluon approach and the meson exchange approach havealso been extended to the multi-strange sector [108–110].Here, the interaction requires either annihilation of twoquark-antiquark pairs, or in the meson picture, exchangeof two kaons. This means that the interactions occur atshorter distances which make double-strange productionmore suitable for establishing the relevant degrees of free-dom. The clearest difference between the quark-gluon pic-ture and the kaon exchange picture is typically found inthe predictions of spin observables e.g. polarisation andspin correlations.Understanding the mechanism of hyperon productionis also important in order to correctly interpret experi-mental data on other aspects of hyperons. One exampleare recent theoretical and experimental studies of the hy-peron structure in e + e − → Λ ¯ Λ . In Ref. [111], the time-likeform factors G E and G M were predicted, including theirrelative phase ∆Φ = Φ ( G E ) − Φ ( G M ) that manifests itselfin a polarised final state. Different potential models wereapplied, using ¯ pp → ¯ ΛΛ data from PS185 [112] as input.In the model predictions for the channel e + e − → Λ ¯ Λ , the (a) (b) Figure 6: (a)
The Λ decay frame. The opening angle between the polarisation axis and the outgoing proton θ p is shown. (b) Production plane of the pp → ΛΛ reaction. The y -axis of the Λ decay frame is perpendicular to the production plane. The z -axis is in the direction of the outgoing Λ with respect to origin in the centre-of-mass frame. total cross section and the form factor ratio R = | G E /G M | differ very little for different potentials. However, the rela-tive phase ∆Φ and hence the Λ polarisation showed largesensitivity. New data from BESIII [113] provide an in-dependent test of the Λ ¯ Λ potentials. Another example ishyperons and antihyperons in atomic nuclei, since under-standing the elementary ¯ pp → ¯ Y Y reactions is crucial inorder to correctly interpret data from ¯ pA collisions.Spin observables are straight-forward to measure forground-state hyperons thanks to their weak, self-analysingdecays. This means that the decay products are prefer-entially emitted along the spin direction of the parenthadron. Consider a spin hyperon Y decaying into a spin baryon B and a pseudoscalar meson M . The angulardistribution of the daughter baryon B is related to thehyperon polarisation by I (cos θ B ) = 14 π (1 + α Y P y cos θ B ) (1)as illustrated in Fig. 6a, where α Y [3] is the asymmetryparameter of the hyperon decay related to the interferencebetween the parity conserving and the parity violating de-cay amplitudes. The polarisation P y is related to the pro-duction dynamics, hence it depends on the centre-of-mass(CMS) energy / beam momentum and on the hyperonscattering angle. In strong production processes, such as ¯ pp → ¯ Y Y , with unpolarised beam and target, the polar-isation can be non-zero normal to the production plane,spanned by the incoming antiproton beam and the out-going antihyperon as shown in Fig. 6b. Spin correlationsbetween the produced hyperon and antihyperon are alsoaccessible [114] and from these, the singlet fraction canbe calculated, i.e. the fraction of the hyperon-antihyperonpairs that are produced in a spin singlet state. Additionalinformation can be obtained from hyperons that decayinto other hyperons, e.g. the Ξ . In the sequential decay Ξ − → Λπ − , Λ → pπ − , the additional asymmetry param-eters β and γ of the Ξ − hyperon are accessible via thejoint angular distribution of the Λ hyperons and the pro-tons [115, 116]. For spin hyperons, e.g. the Ω − , the spinstructure is more complicated. Only considering the po-larisation parameters of individual spin hyperons, we find that spin hyperons produced in strong processeslike pp → Ω + Ω − have seven non-zero polarisation param-eters. Three of these can be extracted from the Λ angulardistribution in the Ω − → ΛK − decay [117]. The remain-ing four parameters can be obtained by studying the jointangular distribution I ( θ Λ , φ Λ , θ p , φ p ) of the Λ hyperonsfrom the Ω − decay and the protons from the subsequent Λ decay [116]. The PS185 collaboration have provided a large set of high-quality data on single-strange hyperons [112, 118] pro-duced in antiproton-proton annihilation. One interestingfinding is that the ¯ ΛΛ pair is produced almost exclusivelyin a spin triplet state. This can be explained by the Λ quark structure: the light u and d quarks are in a relativespin-0 state, which means that the spin of the Λ is carriedby the s quark. Various theoretical investigations repro-duce this finding [105–107], but no model has yet beenformulated to describe the complete spin structure of thereaction. The extension of models into the double-strangesector [108, 109] and even the triple-strange Ω [110], havenot been tested due to the lack of data. For Ξ − and Ξ from ¯ pp annihilations, only a few bubble-chamber eventsexist [119], whereas no data at all are available related totriple-strange hyperon production since no studies havebeen carried out so far. As a result, further progress ofthis field is still pending. New data on the spin structureof pp → Y Y for ground-state multi-strange and single-charmed hyperons would therefore be immensely impor-tant for the development of a coherent picture of the roleof spin in strangeness production.
Previous studies of mainly single-, but also a fewdouble strange hyperon-antihyperon pairs produced inantiproton-proton annihilations show remarkably largecross sections within the PANDA energy range [118]. This i.e. all finalstate particles are reconstructed. The lower limits marked with an asterisk ( ∗ ) denote a 90% confidence level. p p Reaction σ ( µ b) Reconstruction Decay S/B Rate ( s − )(GeV/ c ) efficiency (%) at cm − s − pp → ΛΛ Λ → pπ −
114 441.77 pp → Σ Λ Σ → Λγ > 11* 2.46.0 pp → Σ Λ Σ → Λγ
21 5.04.6 pp → Ξ + Ξ − Ξ − → Λπ −
274 0.37.0 pp → Ξ + Ξ − Ξ − → Λπ −
165 0.14.6 pp → ΛK + Ξ − + c . c Ξ − → Λπ − > 19* 0.2 Λ → pπ − means that large hyperon data samples can be collectedwithin a reasonable time even with the reduced luminos-ity of the Phase One setup. Simulation studies of exclu-sive hyperon production, using a simplified Monte Carloframework, were performed and presented in detail inRefs. [117, 120, 121, 123]. New, dedicated simulation stud-ies of hyperon production have been performed for thisreview: – pp → ΛΛ, ¯ Λ → ¯ pπ + , Λ → pπ − at p beam = 1 . GeV/ c . – pp → Σ Λ, ¯ Σ → ¯ Λγ, ¯ Λ → ¯ pπ + , Λ → pπ − at p beam =1 . GeV/ c and p beam = 6 . GeV/ c . – pp → Ξ + Ξ − , ¯ Ξ + → ¯ Λπ + , ¯ Λ → ¯ pπ + , Ξ − → Λπ − , Λ → pπ − at p beam = 4 . GeV/ c and p beam = 7 . GeV/ c .The beam momenta for the single-strange hyperons werechosen in order to coincide with those of other benchmarkstudies. For the double-strange Ξ − , the chosen beam mo-menta coincide with the hyperon spectroscopy campaign(4.6 GeV/ c , see Section 5.2) and the χ c (3872) line-shapecampaign (7 GeV/ c , see Section 6.2.2). In these new sim-ulation studies, a realistic PandaROOT implementationof the Phase One conditions was used, though with somesimplifications due to current limitation in the simulationsoftware: i) ideal pattern recognition, with some additionalcriteria on the number of hits per track in order to mimica realistic implementation of the track reconstruction ii)ideal PID matching, to reduce the run-time. It was how-ever shown in Ref. [117] that the event selection can beperformed without PID thanks to the distinct topologyof hyperon events: since the hyperons have relatively longlife-time ( − s) they travel a measurable distance be-fore decaying. This provides a challenge in the trackingbut also makes the background reduction very efficient.Around events were generated for ¯ ΛΛ and ¯ Ξ + Ξ − [122, 123], whereas events for ¯ Σ Λ [124]. The largerevent samples in the ¯ ΛΛ and ¯ Ξ + Ξ − cases enable stud-ies of spin observables. In the case of ¯ Σ Λ , only a gen-eral feasibility study of cross section and angular distri-bution measurements has been carried out so far. The ¯ ΛΛ and ¯ Σ Λ final states were modelled using parameterisa-tions based on data from Refs. [112, 125], where it wasfound that single-strange antihyperons are very stronglyforward-going in the CMS of the reaction. The ¯ Ξ + Ξ − fi-nal state has never been studied and was therefore gener-ated both with an isotropic angular distribution and with a forward-peaking distribution. The results were found todiffer only marginally.The particles were propagated through the Panda-ROOT detector implementation and the signals were digi-tised, reconstructed and analysed. The signal events wereselected by requiring all stable ( p , ¯ p and γ ) or pseudo-stable ( π + and π − ) particles to be found: – ¯ ΛΛ : p , π − , ¯ p and π + . – ¯ Σ Λ : p , π − , ¯ p , π + and γ . – ¯ Ξ + Ξ − : p , 2 π − , ¯ p and 2 π + .To reduce the number of background photon signals, ad-ditional energy cuts were applied to identify the photonfrom the ¯ Σ decay [124]. The Λ and ¯ Λ , that appear in allchannels, were identified by combining the reconstructedpions and protons/antiprotons and applying vertex fitsand mass window criteria on the combinations. Further-more, the decay vertex of the Λ/ ¯ Λ was required to be dis-placed with a certain distance from the interaction point.To identify ¯ Σ or Ξ − / ¯ Ξ + , the Λ/ ¯ Λ candidates were com-bined with the photons or remaining pions. In the case of ¯ ΛΛ and ¯ Σ Λ , four-momentum conservation was used inkinematic 4C fits to further reduce the background. Sincethe Ξ − decays sequentially, a more elaborate method in-cluding a decay tree fitter was applied [122, 123].The resulting signal efficiencies are given in Table 2,that also includes the results from the Ξ ∗ study describedin Section 5.2.2. The expected rates of reconstructedevents are calculated based on the Phase One luminosityof cm − s − and cross sections from Refs. [112, 125]( ¯ ΛΛ and ¯ Σ Λ ) and Ref. [110] ( ¯ Ξ + Ξ − ). The signal-to-background ratios (S/B) were obtained by simulating events at each energy, generated with the Dual PartonModel [41].In this work, we have also investigated the feasibilityof reconstructing spin observables such as the polarisationand spin correlations using the methods outlined in Ref.[117]. For the analysis, the pp → ΛΛ, ¯ Λ → ¯ pπ + , Λ → pπ − sample was used, containing 157000 signal events surviv-ing the selection criteria. A sample of this size can becollected within a few hours with the Phase One lumi-nosity. The simulated events were weighted according toan input polarisation function P y = sin 2 θ Λ and the spincorrelation distributions C ij = sin θ Λ ( i, j = x, y, z ). Sym-metry implies P Y = - P ¯ Y which means that the extracted polarisation from Λ and ¯ Λ can be combined for betterstatistical precision.The reconstruction efficiency was accounted for us-ing two different, independent methods: i) regular, multi-dimensional acceptance correction as in Ref. [121] andii) using the acceptance-independent method outlined inRef. [117]. The results of the MC simulations were dividedinto bins with respect to the ¯ Λ scattering angle. In eachbin, the polarisation P Y and spin correlations C ij werereconstructed. The resulting polarisation distribution isshown in panel a) of Fig. 7 with acceptance correctionsand in panel b) with the acceptance-independent method.The polarisation distributions extracted with the two in-dependent methods agree with each other as well as withthe input functions. L q Cos - - ) / y + P y ( P - - )/2 y + P y (PInput ANDAP
MC simulation (a) L q Cos - - ) / y + P y ( P - - )/2 y + P y (PInput ANDAP
MC simulation (b)
Figure 7: (a)
Average polarisation of the Λ / ¯ Λ . (b) Average ofthe polarisations reconstructed without any acceptance correc-tion. The vertical error bars are statistical uncertainties only.The horizontal bars are the bin widths. The red solid line markthe input polarisation as a function of cos θ Λ . In the same way, spin observables of the Ξ − hyperonswere studied at both 4.6 GeV/ c and 7.0 GeV/ c . The num-ber of signal events were . · and . · , respectively,samples that can be collected within a few days duringPhase One. The resulting polarisation distributions as afunction of cos θ Ξ obtained at each energy are shown inFig. 8. The singlet fractions were calculated from the spin correlations and are shown in Fig. 9. A singlet fraction of 0means that all Ξ − ¯ Ξ + states are produced in a spin tripletstate, a fraction of 1 means they are all in a singlet state,and a fraction of 0.25 means the spins are completely un-correlated. In Ref. [109], the singlet fraction is predicted tobe 0 for forward-going ¯ Ξ + and closer to 1 in the backwardregion. This is in contrast to the single-strange case whenthe singlet fraction is almost independent of the scatteringangle [118]. The results of the simulations shown in Fig. 9indicate that the uncertainties in the singlet fraction willbe modest at all scattering angles, which enables a precisetest of the prediction from Ref. [109]. + X q Cos - - ) / y + P y ( P - - )/2 y + P y (PInput ANDAP
MC simulation (a) + X q Cos - - ) / y + P y ( P - - )/2 y + P y (PInput ANDAP
MC simulation (b)
Figure 8: (a)
Average polarisation of the Ξ − / ¯ Ξ + at 4.6 GeV/ c . (b) Average of the polarisation of Ξ − / ¯ Ξ + at 7.0 GeV/ c . Thevertical error bars are statistical uncertainties only. The hor-izontal bars are the bin widths. The red solid line mark theinput polarisation as a function of cos θ Ξ . Most systematic effects that are important in cross sec-tion measurements, e.g. trigger efficiencies and luminos-ity, are expected to be isotropically distributed in a near π experiment like PANDA. This means that their im-pact on angular distributions, and parameters extractedfrom these, are expected to be small. Hyperon polarisationstudies with BESIII ( e.g. [113]) instead indicate that im-perfections in the Monte Carlo description of the data,due to for example gain drift in HV supplies, may bemore important. Most of these effects can however only + X q Cos - - S i ng l e t f r a c t i on S FInput
ANDAP
MC simulation (a) + X q Cos - - S i ng l e t f r a c t i on S FInput
ANDAP
MC simulation (b)
Figure 9: Reconstructed Singlet Fraction F S at (a) p beam = 4 . GeV/ c and (b) p beam = 7 . GeV/ c . The red curves are theinput Singlet Fraction. The dashed line indicates values corresponding to a statistical mixture of singlet and triplet final states. be studied once PANDA is operational and by carefulMonte Carlo modelling, they can be minimised. In thesimulation studies presented here, three basic consistencytests have been performed in order to reveal eventualsensitivity to detection- and reconstruction artefacts: i)comparison between generated and reconstructed and ef-ficiency corrected distributions ii) comparison between ex-tracted hyperon and antihyperon parameters iii) compar-ison between two different efficiency correction methods.All three tests show differences that are negligible withrespect to the small statistical uncertainties. Baryon spectroscopy has been decisive in the developmentof our understanding of the microscopic world, the best ex-ample being the plethora of new states discovered in the1950’s and 1960’s. It was found that these states couldbe organised according to “the Eightfold Way", i.e.
SU(3)flavour symmetry, that led to formulation of the quarkmodel by Gell-Mann and Zweig [126]. Though successfulin classifying ground-state baryons and describing some oftheir ground-state properties, the quark model fails to ex-plain some features of the baryon excitation spectra. Thisindicates that the underlying picture is more complicated.In contemporary baryon spectroscopy, the most intriguingquestions are i) Which effective degrees of freedom are ad-equate to describe the hadronic reaction dynamics? Whichbaryonic excitations are efficiently and well described in athree-quark picture and which are generated by coupled-channel effects of hadronic interactions? ii) To which ex-tent do the excitation spectra of baryons consisting of u,d, s obey SU(3) flavour symmetry? iii) Are there exoticbaryon states, e.g. pentaquarks or dibaryons?Among the theoretical tools available to study thespectra and internal properties of baryons, lattice QCDapproaches have received a lot of attention thanks to the tremendous progress over the past years. Prominent exam-ples are the mass prediction of the double charm groundstate Ξ cc baryon [127–131], now confirmed by LHCb [132],and accurate Lattice calculations of the mass splitting ofthe neutron and proton [133].However, for the excited states in the light-baryon sec-tor differences between recent calculations [134, 135] re-main and unambiguous conclusions cannot yet be drawn.Other approaches to baryon excitation spectra are basedon the Dyson-Schwinger framework [136], and on thecoupled-channel chiral Lagrangian [137–140].The next step is systematic studies of the strange sec-tor, in particular states with double and triple strangeness.These bridge the gap between the highly relativistic lightquarks and the less relativistic heavy ones. So far, worldwide experimental efforts in baryon spec-troscopy have been focused on N ∗ and ∆ resonances. Mostof the known states have masses smaller than 2 GeV/ c and were discovered in πN scattering experiments. Inrecent years, many laboratories (JLab, ELSA, MAMI,GRAAL, Spring-8 etc) have studied these resonances inphoton-induced reactions [141, 142]. As a result, the databank on nucleon and ∆ spectra has become significantlybigger and a lot has been learned. However, there are sev-eral puzzles that remain to be resolved.One example is the so-called missing resonance prob-lem of Constituent Quark Models (CQMs): many statesthat are expected from these phenomenological-drivenmodels have not been observed experimentally. This isin contrast to the Dyson-Schwinger approach whose pre-dictions agree almost one-to-one with the experimentallymeasured light baryon spectra below 2 GeV [143,144]. Thisobservation demonstrates the shortcomings of CQMs, thereby motivating the necessity to experimentally estab-lish the spectra of excited baryons. For a successful cam-paign, an experimental approach is needed in which thesestates are searched for and their properties are studied us-ing various complementary initial probes such as πN , γN ,and, with PANDA, ¯ pN .Another example of an unresolved conundrum is the level ordering : The lightest baryon, i.e the nucleon, has J P =
12 + and the next-to-lightest baryon is expected to beits parity partner, with J P = − . However, this is in con-trast to experimental findings where the Roper N ∗ (1440) resonance, with J P =
12 + , is significantly lighter than thelightest J P = − state, i.e. the N ∗ (1535) .A new angle to the aforementioned puzzles can be pro-vided by studying how they carry over to strange baryons.In the single-strange sector, the missing CQM resonanceproblem remains. Regarding the level-ordering, the situ-ation is very different regarding light baryons: the paritypartner of the lightest Λ hyperon is the Λ (1405) which isindeed the next-to-lightest isosinglet hyperon [145]. How-ever, the Λ (1405) is very light, and, therefore, it has beensuggested to be a molecular state, see e.g. Ref. [146, 147].The existing world data on double- and triple-strangebaryons are very scarce and do not allow for the kindof systematic comparisons with theory predictions thatled to progress in the light and single-strange sector. Onlyone excited Ξ state and no excited Ω states are consideredwell established within the PDG classification scheme [3].It is also worth pointing out that even for the groundstate Ξ and Ω , the parity has not been determined exper-imentally. Furthermore, the spin determination of the Ω is not model-independent but inferred by assumptions onthe Ξ c and Ω c spin [148]. It would be very illuminatingto study the features of the double- and triple-strange hy-peron spectra since it enables a systematic comparison ofsystems containing different strangeness. A dedicated simulation study has been performed of the ¯ pp → ΛK − Ξ + + c.c. reaction at a beam momentum of4.6 GeV/ c . In the following, the inclusion of the chargeconjugate channel is implicit. In spectroscopy, parameterslike mass, widths and Dalitz plots are essential. There-fore, the focus of this study is to estimate how well suchparameters can be measured with PANDA. The simulateddata sample of 4.5 · events includes the Ξ (1690) ± and Ξ (1820) ± resonances, decaying into ΛK − + c.c. (each40% of the total generated events), as well as non-resonant ΛK − Ξ + + c.c. production (20% of the generated sam-ple). The simulated widths of the Ξ (1690) − and Ξ (1820) − resonances were 30 MeV/ c and 24 MeV/ c , respectively,in line with the PDG [3]. The event generation was per-formed using EvtGen [149] with the reaction topology asillustrated in Figure 10. The angular distribution of theproduced Ξ ∗ resonance are isotropically generated sinceno information from experimental data exist. The analysis was performed in the same way as de-scribed in Section 5.1.2. The final state is required tocontain p , ¯ p , π − , π + , K − and K + . The Λ candidateswere identified by combining p and π − into a commonvertex and applying a mass window criterion. The Ξ − ( Ξ ∗ ) hyperons were identified by combining Λ candidateswith the remaining pions (kaons). Background was fur-ther suppressed by a decay tree fit in the same way as inSection 5.1.2. The exclusive reconstruction efficiency wasfound to be 5.4%. We assume a ¯ pp → ¯ ΛKΞ + c.c. cross sec-tion of 1 µ b, where the production mainly occurs througha Ξ − Ξ ∗ + c.c. pair and where the excited cascade couldbe either Ξ ∗ (1690) or Ξ ∗ (1820) . With this assumption,the reconstruction rate is 0.2 s − or 18000 events per day.These cross sections have never been measured and as-sumed of the same order as the ground-state ¯ Ξ + Ξ − [150]that was measured by Ref. [119] to be around µ b.The background was studied using a DPM sample con-taining events and the signal events were weighted as-suming a total cross section of 50 mb. No backgroundevents survived the selection criteria and we thereforeconclude that on a 90% confidence level, the signal-to-background is S/B > . The numbers are summarised inTable 2.The reconstructed Dalitz plot and ΛK − invariant massare shown in Figure 11. The reconstruction efficiency dis-tribution is flat with respect to the Dalitz plot variablesand the angles. This is a necessary condition in order tominimise systematic effects in the planned partial-waveanalysis of this final state.In order to evaluate the Ξ and ¯ Ξ resonance parame-ters, the ΛK − and ¯ ΛK + mass distributions have been fit-ted with two Voigt functions combined with a polynomial.By comparing the reconstructed ΛK − and ¯ ΛK + widthsto the generated ones, the mass resolution was estimatedto σ M = 4 . for the Ξ (1690) − and σ M = 6 . forthe Ξ (1820) − . The obtained fit values are shown in Table3. In both cases, the fitted masses are in good agreementwith the input values. PANDA will be a strangeness factory where many differ-ent aspects of hyperon physics can be studied. Double- andtriple strange hyperons are unknown territory both whenit comes to production dynamics, spin observables andspectroscopy. Long-standing questions, such as relevantdegrees of freedom and quark structure, can be investi-gated already during the first years with reduced detectorsetup and luminosity. Furthermore, the measurements inPhase One provide important milestones for the foreseenprecision tests of CP conservation, that will be carried outwhen the design luminosity and the full PANDA setup areavailable in the subsequent Phase Two and Three. In thelatter, copious amounts of weak, two-body hyperon decayswill be recorded - several million exclusively reconstructed ¯ ΛΛ pairs every hour. This enables precise measurementsof the decay asymmetry parameters. In the absence of CPviolation, the asymmetry parameters of a hyperon have p p Ξ* – Ξ + ΛΛK – π + π – ppπ + Figure 10: A schematic view of the reaction topology used for the generation of Monte Carlo events.Table 3: Fit values for
Λ K − and Λ K + . Λ K − Λ K + Ξ (1690) − Ξ (1820) − Ξ (1690) + Ξ (1820) + Fitted mass [GeV /c ] 1.6902 ± ± ± ± Γ [MeV /c ] 31.09 ± ± ± ± /c ] 1.6900 1.8230 1.6900 1.8230Input Γ [MeV /c ] 30 24 30 24 the same magnitude but the opposite sign of those ofthe antihyperon, e.g. α = − ¯ α . Differences in the decayasymmetry therefore indicate violation of CP symmetry.The ¯ pp → ¯ Y Y reaction provides a clean test of CP vi-olation, since the initial state is a CP eigenstate and nomixing between the baryon and antibaryon is expected tooccur. Since hyperons and antihyperons can be producedand detected at the same rate and in very large amounts,the prospects are excellent for ground-breaking symme-try tests that could help us to understand the matter-antimatter asymmetry of the Universe. In addition, PhaseThree opens up the possibility to study also single-charmhyperons. A systematic comparison between the strangeand the charm sector will be an important step towards acoherent understanding of non-perturbative QCD at dif-ferent scales.
The original constituent quark model (CQM) describesmesons and baryons. In CQM, mesons are described asquark-antiquark states ( q ¯ q ) interacting through a poten-tial. One of the motivations for this description was thenon-observation of mesons with strangeness or chargelarger than unity, neither had states been observed with other spin and parity combinations than those consis-tent with fermion-antifermion pairs. However, QCD allowsfor any colour-neutral combination of strongly interactingquarks and gluons and therefore, CQM-based models canbe extended to incorporate the dynamics of glueballs, hy-brids and multiquarks. These states are often referred toas QCD exotics .Glueballs ( gg or ggg ) are formed due to the self-coupling of the colour-charged gluons. This unique featureof the strong interaction is of particular interest since theglueball mass has no contribution from the Higgs mecha-nism. Instead, it is completely dynamically generated bythe strong interaction. Most glueballs predicted by QCDor phenomenological models have the same quantum num-bers as mesons and hence they can mix. As a consequence,it is a challenge to unambiguously determine the glueballfraction of an observed hadronic state.In addition to glueballs, there are meson- or baryon-like states for which QCD admits a gluonic componentcalled hybrids, e.g. q ¯ qg . Hybrids can, in addition tothe spin-parity combinations allowed for regular hadrons,also have spin-exotic quantum numbers. To establish theexistence of hybrids experimentally, the decompositionof quantum numbers requires sophisticated partial-waveanalysis (PWA) tools and large data samples.Also other colourless combinations of multiquark res-onances are allowed within QCD. The study of multi- ] /c ) [GeV - , K Λ ( M2.6 2.8 3 3.2 3.4 3.6 3.8 ] / c ) [ G e V - , K + Ξ ( M final sample reco - K Λ + Ξ C o un t s (a) ] M [GeV/c1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95 2 c oun t s final samplereco (b) Figure 11: (a)
The reconstructed Dalitz plot of the ΛK − Ξ + final state. (b) The ΛK − invariant mass of the reconstructedMC data. quarks has experienced tremendous progress during thelast decade. Examples of multiquark states are tetraquarks ( qq ¯ q ¯ q ) or pentaquarks ( qqqq ¯ q ). However, many open ques-tions remain, in particular about the internal structureof the observed states. Precision measurements of variousresonance properties are needed, as well as ab-initio theo-retical predictions, in order to reach deeper insights aboutthe structure of multiquark states.The search for exotic hadrons is being carried out atseveral energy scales, from the light u and d scale to thebottom quark scale. A fundamental question to be an-swered concerns the relevant degrees of freedom – shouldexcited light hadrons be described in terms of quarks andgluons, or are various dynamical effects, e.g. at mesonpair thresholds, more important? In the light quark sec-tor, many resonances are broad and overlap in mass. Thismeans that they mix if they have the same quantum num-bers. The advantage of the light sector is that the produc-tion cross sections are generally large, allowing for largedata samples to be collected within a short time. This isan advantage when determining spin and parity throughpartial-wave analyses.The physics of hidden-charm states, such as charmo-nium, is expected to be very different due to the highermass of the charm quark ( m c (cid:39) c > Λ QCD ). Thestrong coupling constant in this region is α s ≈ . , cor- responding to an energy scale barely below the region inwhich perturbation theory starts to break down. At theseenergies, quark and gluon degrees of freedom become rel-evant. The velocity of the charm quark is relatively small, ( v/c ) ∼ m c (cid:29) m c v/c (cid:29) m c ( v/c ) ) makesheavy-quark systems, such as charmonium, ideal probesto study the transition between perturbative and non-perturbative regimes [153, 154].Meson-like systems composed of heavy and light con-stituent quarks, such as open-charm states, are comple-mentary to that of hidden-charm meson-like states. Alsohere, various striking experimental observations have beenmade in the past [156, 157] pointing to the possible exis-tence of narrow resonances that do not fit into the con-ventional heavy-light meson pattern. A recent example isthe intriguing observation of LHCb, speculating the ex-istence of an open-charm tetraquark with a mass around2.9 GeV/ c [151]. Besides spectroscopy aspects, ground-state open-charm states decay weakly, providing access to, e.g. , semi-leptonic form factors. The field of open-charmspectroscopy and electro-weak processes will become ac-cessible in the later stages of PANDA, beyond that ofPhase One. Its success depends on the completion of thevertex reconstruction capabilities of PANDA and higherluminosities for excellent statistical significance. Differen-tial cross section measurements will be accessible in PhaseOne, which allows for unique studies of the productionmechanism of pairs of open-charm meson and baryons inantiproton-proton collisions. Such measurements have thepotential to study the intrinsic charm content of the nu-cleon and, thereby, shed light on the recently predictednonvanishing asymmetric charm-anticharm sea from lat-tice QCD [155].In the following, we discuss the Phase One perspectivesof the meson-like spectroscopy programme of PANDA atvarious mass scales, starting from the light-quark sectorto the hidden-charm region. Lattice QCD calculations have resulted in detailed predic-tions for the glueball mass spectrum in the quenched ap-proximation and more exploratory results in unquenchedsimulations [158]. There is consensus that the ground-state is a scalar ( J P C = 0 ++ ) in the mass range ofabout /c which leads to mixing with nearby q ¯ q states [159]. Mixing scenarios include e.g. the observed f (1370) , f (1500) and f (1710) . Detailed experimentalstudies of their decay patterns, carried out mainly inantiproton annihilation experiments at CERN (CrystalBarrel and OBELIX at LEAR) [160–177] and at Fermi-lab (E760 and E835) [178, 179], confirm this picture. A pseudoscalar glueball is predicted by lattice QCD above /c . The much lighter η (1440) has been suggestedas a candidate, though it is unclear whether this is onesingle resonance or two ( η (1405) and η (1475) ) [3]. Thepossible existence of a η (1275) complicates the picture fur-ther [180].The lightest tensor ( J P C = 2 ++ ) glueball is predictedin the mass range from to . /c [159]. The possiblemixing of two nonets ( P and F ) results in five expectedisoscalar states. The JETSET collaboration at LEAR hasreported a tensor component in the mass range around . /c in the ¯ pp → φφ reaction [181]. However, dueto the limited size of the data sample, no firm conclusionscould be drawn.In the vicinity of meson-pair production thresholds,narrow meson-like excitations can appear. Prominent ex-amples in the light quark sector are the a (980) and the f (980) scalar mesons. These states are strongly attractedby the K ¯ K threshold and are believed to have a large K ¯ K component. The narrow vector meson φ (2170) , discoveredby BaBar [182], is particularly interesting in this context.It does not fit into the q ¯ q model, it is comparatively narrow( ≈
83 MeV ) and the mass is close to the φf (980) thresh-old. It is debated whether the φ (2170) is an s ¯ s tetraquarkor hybrid state [183]. Close to the K ∗ ¯ K threshold, theCOMPASS collaboration discovered a relatively narrow( Γ ≈
153 MeV ) axial-vector meson, the a (1420) [184].It has been interpreted as the isospin partner of the es-tablished f (1420) [185]. The latter can be attributed amolecular-type K ¯ Kπ component [186], opening up for apossibility that also the a (1420) is a molecular-type state.The first coupled-channel calculation related to a potentialaxial-vector molecule state originates from [187]. There arefurther interpretations proposed such a triangle singular-ity from rescattering of the a (1260) [188]. There has beensignificant progress in recent years in lattice scattering andcoupled channel calculations including in the light mesonsector [189, 190].Several experiments have reported large intensitiesin the spin-exotic − + wave, referred to as π (1400) , π (1600) and π (2015) [191]. Whereas the resonant natureof the π (1400) and the π (2015) is disputed, the π (1600) is currently the strongest light hybrid candidate, recentlyre-addressed in COMPASS data [192–195]. This impliesthe existence of so far undiscovered nonet partners. In the search for exotic hadrons, the gluon-rich environ-ment and the access to all ¯ qq -like quantum numbers information, gives PANDA a unique advantage compared to e + e − experiments. Furthermore, states with non- q ¯ q quan-tum numbers can be accessed in production.The reaction ¯ pp → φφ is considered suitable for tensorglueball searches, since the production via intermediateconventional q ¯ q states is OZI suppressed in contrast toproduction via an intermediate glueball. Already duringPhase One of PANDA, we will collect data samples ofthis reaction that are two orders of magnitude larger than achieved by previous experiments. A potential tensor com-ponent would reveal itself in energy scans and amplitudeanalyses.The f (1420) can be identified through the decay to K ¯ Kπ and studied at a centre-of-mass energy of about .
25 GeV in ¯ pp → π + π − + K ¯ Kπ and ¯ pp → π /η + K ¯ Kπ .In the latter cases, the amplitude analysis is simpler sinceonly one recoil ( π or η ) is involved. The a (1420) can beaccessed in π combinations from the ¯ pp → π + π − π + π − reaction. The COMPASS analysis shows that very largesamples are required [184]. Here, PANDA will profit fromthe large expected production cross sections in ¯ pp anni-hilations. The cross sections for pion modes are in theorder of mb, while reactions involving kaons are in theorder of µ b . The observed intensity of f (1420) in ¯ pp → K + K π − π + π − is about [196]. This makes theprospects excellent for studying the f (1420) as well assearching for the a (1420) in ¯ pp annihilations already dur-ing Phase One of PANDA.Furthermore, insights on the nature of the φ (2170) will be obtained by studying other production mechanismsand hitherto unmeasured decay patterns. At PANDA, the φ (2170) will be accessible in reactions involving π , η , or π + π − recoils at centre-of-mass energies of about . .In a similar way, searches for hybrid candidates such as π (1400) , π (1600) and π (2015) can be performed. In 2003, the discovery of a signal in the
J/ψπ + π − chan-nel near the D ¯ D ∗ threshold completely changed our un-derstanding of the charmonium spectra [197]. Up to thispoint, the quark model originally published in 1978 [198]had been very successful in describing all observed states.However, the new signal, established the state denoted χ c (3872) or X (3872) , turned out to have propertiesat odds with the quark model. After 2003, many morestates in the charmonium and bottomonium mass rangewere discovered. While all states below the lowest S -wave open charm threshold behave in accordance with thequark model, the states above fit neither in mass nor inother properties. This family of exotic states is now re-ferred to as the XY Z states. Arguably the most promi-nent states, besides the aforementioned χ c (3872) , are thevector-meson states Y (4260) [199] and Y (4360) [200] aswell as the charged states Z (4430) [201], Z c (3900) [202], Z c (4020) [203], Z cs (3985) [204] in the charmonium sec-tor and the charged states Z b (10610) and Z b (10650) [205]in the bottomonium sector. The most viable interpreta-tions of these states are hybrid mesons (quark states withan active gluon degree of freedom), compact tetraquarks(bound systems of diquarks and anti-diquarks), hadro-quarkonia (a compact heavy quarkonium surrounded by alight quark cloud) and hadronic molecules (bound systemsof two mesons; when located very near the relevant S -wavethreshold these can be very extended). Recent reviews ofvarious calculations can be found in Refs. [9–11, 15]. In particular the Z states – charged states decaying into finalstates that contain both a heavy quark and its antiquark— have received a lot of attention since they must containat least four quarks [206]. In addition, lattice calculationspredict a supermultiplet of hybrid mesons including exoticquantum numbers with a similar pattern in both charmo-nium and bottomonium [207].As of today there is no consensus which one of the men-tioned models explains the properties of the XY Z statesbest. Clearly more experimental information is needed tomake progress. The two most pressing issues are: – Where are the spin partner states of the observed
XY Z states? Their location contains valuable infor-mation about the most prominent component of thestates, since different assumptions lead to different ef-fects of spin symmetry violation [208]. PANDA is wellprepared to hunt for those spin partner states, sincethe production mechanism is not constrained to cer-tain quantum numbers. – What is the line shape of the near threshold states?This allows one to especially investigate the role of thetwo-meson component in a given state, since a stronglycoupled continuum necessarily leaves an imprint in theline shapes [15]. Moreover, a virtual state cannot havea prominent compact component [209].PANDA can provide a significant contribution to answerthese questions, in particular the second one, already inPhase One. Precision measurements of line-shape param-eters of resonances provide crucial information that shedslight on their internal structure. The determination ofthese parameters for narrow states is particularly chal-lenging and requires a facility with sufficient resolution toreach the necessary sensitivity.In the following, we illustrate this by discussing thecapability of PANDA to perform resonance energy scans,using the famous χ c (3872) state with J P C = 1 ++ as abenchmark. The χ c (3872) has a small natural width; un-til recently the 90% C.L. upper limit was estimated to be1.2 MeV [210]. A new measurement from the LHCb dataare compatible with an absolute Breit-Wigner decay widthof Γ = 1 . ± . ± . MeV for the χ c (3872) . However,a Flatté-like line shape model where the state is describedby a resonance pole with a Full-Width-at-Half-Maximumof about 220 keV [211] is equally probable. The result fromLHCb emphasises the need for precision line-shape mea-surements with significantly better mass resolution thanoffered by experiments that rely on the detector resolu-tion, typically around a few MeV. Only experiments likePANDA, where these resonances are accessible in forma-tion, offer a direct and thus model-independent measure-ment of the line-shape.The analysis presented in the following is meant as ademonstration of the precision capabilities of PANDA, butthe technique can be applied to extract key properties ofother resonances as well. PANDA offers a unique possibility to reach sub-MeV res-olution exploiting the cooled antiproton beam from theHESR. This has been demonstrated by a feasibility studyof the χ c (3872) line-shape measurement, to be carried outin a future energy scan designed to precisely measure ab-solute decay widths and line shapes [212]. The χ c (3872) ,as well as all other non-exotic J P C combinations, can becreated in formation in ¯ pp annihilation.The details of the PANDA feasibility study can befound in Ref. [212]. In this paper, we focus on the condi-tions expected for Phase One. This implies an HESR beammomentum spread (beam energy resolution) of d p/p =5 · − (d E CMS = 83 . keV) and an integrated luminosityof L = · nb) − .The reaction of interest is the direct formation ¯ pp → χ c (3872) , where the χ c (3872) is identified by the twoleptonic J/ψ decay channels χ c (3872) → J/ψρ → e + e − π + π − and χ c (3872) → J/ψρ → µ + µ − π + π − . Thereconstruction efficiencies are . and . , respec-tively, as determined with Monte Carlo simulations in-cluding a realistic GEANT detector implementation. Thephysics parameters as summarised in Tab. 4, have beenused as input.In our study, we quantify i) the sensitivity of an ab-solute measurement of the natural decay width Γ ii) thecapability to distinguish two scenarios: a loosely bound ( D - ¯ D ∗ ) molecular state and a virtual scattering state.Both scenarios have been studied under the assump-tion that PANDA will collect data in 40 energy pointsduring 2x40 days of beam time, i.e. two days per energypoint, with the Phase One operation conditions. This isconsidered a reasonable amount of time to allocate for thiskind of measurements, especially since data for other pur-poses, e.g. hyperon-antihyperon pair production, can becollected in parallel.The parameter Γ is determined by fitting a Voigtfunction, i.e. a convolution of a Breit-Wigner with a nat-ural decay width Γ and a Gaussian with a standard devi-ation σ Beam , accounting for the beam momentum uncer-tainty.The molecular line shape differs significantly from thatof a less sophisticated Breit-Wigner-like resonance shape.It depends on the given decay channel (here
J/ψπ + π − )and on the dynamic Flatté parameter E f [213, 214] (orthe equivalent inverse scattering length, γ in [215]), thatparameterise the nature for a bound or virtual state.For each of the six different input signal cross-sections, σ S = (150 , , , , , nb, the full procedure of sim-ulation, PDF generation and Breit-Wigner/Molecule lineshape fitting has been carried out, employing a maximum-likelihood method.The resulting sensitivities in terms of the relative un-certainty ∆Γ meas /Γ meas of the measured decay width aresummarised for the Breit-Wigner case in Fig. 12. The cor-responding sensitivity for the molecule case is parame-terised in terms of the misidentification probability P mis = N mis − id /N MC . The P mis as a function of the input Flattéparameter E f , is shown in Fig. 13. B ( X → J/ψρ ) B ( J/ψ → e + e − ) B ( J/ψ → µ + µ − ) B ( ρ → π + π − )
100 % [3] σ ¯ pp → X, max
50 nb [216, 218][20, 30, 75, 100, 150] nb σ B, DPM
46 mb [150] σ B, NR t scan
80 dNo. of scan points N scan Γ X [50 , , , , , , keVLine-shape parameter E f − [10 . , . , . , . , . , . , . , . MeV [keV] G [ % ] m ea s G / m ea s GD = 150 nb S s PANDA
MC study [keV] G [ % ] m ea s G / m ea s GD = 100 nb S s PANDA
MC study [keV] G [ % ] m ea s G / m ea s GD = 75 nb S s PANDA
MC study [keV] G [ % ] m ea s G / m ea s GD = 50 nb S s PANDA
MC study [keV] G [ % ] m ea s G / m ea s GD = 30 nb S s PANDA
MC study [keV] G [ % ] m ea s G / m ea s GD = 20 nb S s PANDA
MC study
Figure 12: Sensitivity to the absolute Breit-Wigner width, parameterised in terms of the relative uncertainties ∆Γ meas /Γ meas ,shown as a function of the input decay width Γ of a narrow resonance for six different input signal cross-section σ S . All resultsare extracted for the Phase One HESR running mode. The inner error bars represent the statistical uncertainties and theouter the systematic ones. The bracket markers indicate the corresponding numbers for the case of DPM [41] and non-resonantbackground upscaling according to [220], ignoring statistical and systematic errors. The available computing resources result in limitedsamples of DPM [41] background. This, in combinationwith an efficient background suppression of the order (cid:15) B, gen ≈ · − , results in a very small number of sur-viving background events which introduces an uncertainty.The impact is estimated by scaling up the number of back-ground events determined from the 90% confidence level upper limit, according to [220]. The uncertainty due tonon-resonant background from p ¯ p → J/ψρ was deter-mined in a similar way. The effect on the sensitivity isrepresented by bracket markers in Figs. 12 and 13.A more compact representation of the results extractedfrom Figs. 12 and 13 is shown in Fig. 14 for the Breit-Wigner scenario (left panel) and the molecule scenario [MeV] f,0 E - - - - - - - [ % ] m i s P = 150 nb S s PANDA
MC study [MeV] f,0 E - - - - - - - [ % ] m i s P = 100 nb S s PANDA
MC study [MeV] f,0 E - - - - - - - [ % ] m i s P = 75 nb S s PANDA
MC study [MeV] f,0 E - - - - - - - [ % ] m i s P = 50 nb S s PANDA
MC study [MeV] f,0 E - - - - - - - [ % ] m i s P = 30 nb S s PANDA
MC study [MeV] f,0 E - - - - - - - [ % ] m i s P = 20 nb S s PANDA
MC study
Figure 13: Sensitivity to the ¯ D ∗ D molecule scenario, parameterised in terms of the mis-identification probability P mis , shownas a function of the input Flatté parameter E f , of the χ c (3872) for six different input signal cross-section σ S . All results areextracted for the Phase One HESR running mode. The inner error bars represent the statistical uncertainty and the outer thesystematic ones. The bracket markers indicate the corresponding numbers for the case of DPM [41] and non-resonant backgroundupscaling according to [220], ignoring statistical and systematic uncertainties. (right panel). In the BW case, the minimum Γ is de-fined by the minimum width, for which a σ sensitiv-ity is achieved in an absolute decay width measurement.This corresponds to a relative uncertainty ∆Γ meas /Γ meas of
33 % . In the left panel of Fig. 14, the 3 σ sensitivity isshown as a function of the input σ ¯ pp → X, max . Trendlinesfor inter- and extrapolation are added using an empiricalanalytical function.In the molecule case, the capability of distinguishinga bound state from a virtual state is quantified in termsof the Flatté parameter difference ∆E f := | E f , − E f , th | ,where E f , is the input Flatté parameter and E f , th | isthe threshold energy separating a bound from a virtualstate. The difference can be extracted from Fig. 13 at P mis = 10 % , assuming E f , th = − . MeV according toRef. [213, 214]. The results are shown as a function of theinput cross section σ ¯ pp → X, max in the right panel of Fig. 14.As expected, the larger the cross section, the better theperformance in resolving small ∆E f .The achievable sensitivities has been calculated for oneout of the six input cross sections, σ S = 50 nb, in line withthe experimental upper limit on p ¯ p → χ c (3872) produc-tion provided by the LHCb experiment. For values of the natural decay width larger than Γ = 110 keV a σ rel-ative error ∆Γ meas /Γ meas better than 33 %, is achievedalready in Phase One with 80 days of dedicated beamtime for one resonance scan measurement. The natureof the state – bound or virtual – can be correctly de-termined with a probability of 90 % probability providedfor ∆E f ≈ keV. The presented work serves as an ex-ample, but the same approach will be applied to narrowresonances in general, achieving sub-MeV resolutions. The planned Phase One line-shape measurement of the χ c (3872) and other states with J P C (cid:54) = 1 −− can reveal theintriguing nature of hadronic states. This leads to new in-sights in the overarching question of the strong interactionand hadronisation at different energy scales.In addition, PANDA has excellent discovery potentialfor hitherto unknown, exotic meson-like states thanks tothe gluon-rich environment provided by ¯ pp annihilationsas well as the access to all ¯ qq -like quantum numbers in for-mation. In particular, this opens up for extensive searches [nb] S s s i gn . ) [ k e V ] s ( m i n G PANDA
MC study [nb] S s = % ) [ M e V ] m i s P ( f E D fi V V fi B PANDA
MC study
Figure 14: Left: Sensitivity in terms of Γ min for a 33 % relative error ( σ ) BW width measurement. Right: Sensitivity in termsof the Flatté parameter difference ∆E f for a misidentification of P mis = 10 % for the molecular line-shape measurement. Theblack circles represent a bound molecular state misidentified as a virtual state ( P mis , B → V ) and the blue diamonds a virtual statemisidentified as a bound molecular state ( P mis , V → B ). for spin partners of the XY Z states. Discoveries and mea-surements of the properties of spin partners provide valu-able insights on the prominent components, since differentassumptions lead to different effects of spin symmetry vi-olation [208].In later phases of PANDA, when the design luminos-ity is reached, studies of hadrons with open charm willcommence. The structure and dynamics of these systems,composed of heavy and light constituent quarks, are com-plementary to that of hidden-charm meson-like states.The decay of the lowest lying states occurs primarily viaweak processes, providing experimental access to the semi-leptonic form factors and the CKM parameters. Moreover,spectroscopy studies of the excited states can provide newinsights in the non-perturbative QCD domain that arenot accessible in the hidden-charm sector. This opens thepossibility to search for exotic open-charm states. Hence,PANDA can build upon the BABAR and CLEO discov-eries of the narrow exotic candidates D ∗ s (2317) [156] and D s (2460) [157], respectively. PANDA has the potentialto measure the width of the D ∗ s (2317) with a resolu-tion in the order of 0.1 MeV via an energy scan nearthe threshold of the associated D ± s D ∗ s (2317) ∓ produc-tion [221] and to search for other higher order excitationsof open-charm states. This is particularly important sincethe width is sensitive to a possible molecular componentof the state [15, 209, 222, 223]. Hadron reactions with nuclear targets provide a great op-portunity to study how nuclear forces emerge from QCD.In particular, these reactions offer an angle to the onsetof colour transparency at intermediate energies, the short-distance structure of the nuclear medium, and the effects of the nuclear potential on hadron properties. Two impor-tant aspects make antiproton probes unique in this regard: – The kinematic threshold for the production of heavymesons (e.g. charmonia, D , D ∗ ) and antibaryons is ac-cessible at small beam momenta. – The existence of two-body annihilation channels atlarge momentum transfer.Close to threshold, the produced particles are rather slowin the laboratory frame. Since the coherence lengths aresmall compared to the internucleon distance, these parti-cles interact with the nuclear residue as ordinary hadrons.The probability for such multiple interactions is quantifiedby the nuclear transparency T ( A ) and is given by the ratioof the cross section of an exclusive nuclear process withthe corresponding elementary (nucleon) reaction. The an-tiproton beam gives access to hadron channels that aredifficult to study with other probes at low momenta, forexample J/Ψ .Slow particles are influenced by the nuclear mean fieldpotentials. Antiprotons are particularly suitable for im-planting low-momentum antibaryons or mesons into thenuclear environment, where resulting effects of the nuclearpotential on their masses and decay widths can be stud-ied. Nuclear potentials are crucial to gain valuable insightsinto neutron starts [224].At higher beam momenta, the factorisation theoremmentioned in Section 4 becomes valid, splitting the reac-tion into a hard, pQCD calculable part and a soft partdescribed by GPDs. This relies on the assumption thatsoft gluonic exchanges between the incoming and outgo-ing quark configurations are suppressed, which in turn isonly possible if these configurations are colour neutral andhave transverse sizes substantially smaller than the nor-mal hadron size. While well-established at large momen- tum transfer, it is still an open question at which scale thisphenomenon, known as colour transparency (CT), sets in.Interactions at large momentum transfers also probethe short-distance ( ≤ . fm) structure of the nuclearmedium itself. In this region, effects from non-perturbativeQCD discussed in sections 4 to 6 come into play in the dy-namics of the nuclear repulsive core, a rather unexploredterritory [225], which is expected to have an effect on cold,dense nuclear matter such as neutron stars. Nuclei made of protons and neutrons have been studiedfor more than a century. Hypernuclei, where one of the nu-cleons are replaced by a hyperon, and hyperatoms, wherea hyperon is attached to a nucleus in an atomic orbit,have been explored since more than six decades. As a re-sult, valuable information about the nuclear potentials of Λ and Σ − hyperons has been obtained [226].It was recently pointed out in Ref. [227] that in-medium interactions of antibaryons may cause compres-sional effects and may thus provide additional informa-tion on the nuclear EoS [228]. The data for antibaryons innuclei are however rather scarce. So far, only antiprotonshave been subjected to experimental studies. The antipro-ton optical potential has been addressed in studies of elas-tic ¯ pA scattering at KEK [229] and LEAR [230, 231]. Thefits to the angular distributions of the scattered antipro-tons, indicate that the potential has a shallow attractivereal part Re ( V opt ) = − (0 − MeV and a deep imagi-nary part Im ( V opt ) = − (70 − MeV in the centre of anucleus. This is in contrast to results from the analysis ofX-ray transitions in antiprotonic atoms and of radiochemi-cal data. Here, the real part turned out to be much deeper,Re ( V opt ) = − MeV, whereas the imaginary part wasfound to be Im ( V opt ) = − MeV [232]. However, thecalculations of the ¯ pA elastic scattering as well as thoseof antiprotonic atoms, are sensitive to the ¯ p potential atthe nuclear periphery. The production of ¯ p in pA and AA collisions, on the other hand, is sensitive to the antipro-ton potential deeply inside the nuclei and seems to favourRe ( V opt ) = − (100 − MeV at normal nuclear density aspredicted by microscopic transport calculations [233–235].Antiproton absorption cross sections on nuclei as well asthe π + and proton momentum spectra produced in ¯ p an-nihilation nuclei at LEAR calculated within the GiessenBoltzmann-Uehling-Uhlenbeck (GiBUU) model [236] areconsistent with Re ( V opt ) (cid:39) − MeV, i.e. about a factorof four weaker than expected from naive G-parity rela-tions.In Ref. [237] it has been suggested that this discrep-ancy is a consequence of the missing energy dependenceof the proton-nucleus optical potential in conventional rel-ativistic mean-field models. The energy- and momentumdependence required for such an effect can be recoveredby extending the relativistic hadrodynamic Lagrangian by non-linear derivative interactions [237–239], hence mim-icking many-body forces [240]. Since hyperons and anti-hyperons play an important role in the interpretation ofhigh-energy heavy-ion collisions and dense hadronic sys-tems, it needs to be investigated how these concepts carryover to the strangeness sector. However, antihyperons an-nihilate quickly in nuclei and conventional spectroscopicstudies are therefore challenging or even unfeasible. In-stead, quantitative information about the potentials canbe obtained from exclusive antihyperon-hyperon produc-tion in ¯ pA annihilations close to threshold. However, sofar no such experimental data exist on nuclear potentialsof antihyperons. In the absence of feasible spectroscopic methods,schematic calculations performed in Refs. [241–243] indi-cate that the transverse momentum asymmetry α T = p T ( Y ) − p T ( ¯ Y ) p T ( Y ) + p T ( ¯ Y ) , (2)where p T ( Y / ¯ Y ) ) is the transverse momentum of the hy-peron/antihyperon, is sensitive to the depth of the antihy-peron potential. Other observables of interest are polari-sation and coplanarity.As concluded in Section 5.1.2, a unique feature of an-tiproton interactions within the PANDA energy range isthe large production cross sections of hyperon-antihyperonpairs. However, due to the strong absorption of an-tibaryons in nuclei, the exclusive production rate ofantihyperon-hyperon pairs is expected to be smallerin antiproton-nucleus collisions compared to antiproton-proton interactions.Realistic calculations for the Phase One feasibility havebeen performed using the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) transport model [244]. Here we showrecent results obtained with GiBUU, release 2017, whichincorporates, inter alia, updates in the kaon dynamics andan improved parametrisations of the hyperon-nucleon (S= -1) collision channels at low hyperon momenta withrespect to the previously used release 1.5 [243, 245]. Non-linear derivative interactions were not included. A simplescaling factor ξ p = 0.22 was applied for the antiprotonpotential to ensure a Schrödinger equivalent antiprotonpotential of about 150 MeV at saturation density [236].Since no experimental information exists so far for anti-hyperons in nuclei, G-parity symmetry was adopted as astarting point. The calculations were carried out for dif-ferent values of the antihyperon scaling factor ξ Y . Thecalculations were performed for the following cases: – ¯ ΛΛ pair production in ¯ p + Ne interactions at p beam =1 . GeV/ c . – ¯ ΛΛ pair production in ¯ p + Ne interactions at p beam =1 . GeV/ c . – ¯ ΛΣ − pair production in ¯ p + Ne interactions at p beam = 1 . GeV/ c . – ¯ Ξ + Ξ − pair production in ¯ p + C interactions at p beam = 2 . GeV/ c .A beam momentum of 1.64 GeV/ c is also used for thestudy of the pp → ΛΛ which will serve as a point of ref-erence. At the lower beam momentum of 1.52 GeV/ c , theproduction of Σ is strongly suppressed, hence reducingexperimental ambiguities.The resulting distributions of transverse asymmetry α T asa function of the longitudinal asymmetry α L , defined inthe same way but with T → L , are shown in Figs. 15 ( ¯ ΛΛ )and 16 ( ¯ ΛΣ − and ¯ Ξ + Ξ − ). For ¯ ΛΛ , we observe a remark-able sensitivity of α T to the potential at negative valuesof α L (Fig. 15), and it is clear that secondary effects donot wipe out the dependence. The large α T sensitivity aswell as the negative shift in α T are linked to the substan-tial Λ transverse momentum smearing due to secondaryscattering.In order to estimate the expected event rate we as-sume an interaction rate of 10 s − , 20% beam loss in theHESR due to the complex target and a reconstruction ef-ficiency of 10%, which is slightly smaller than that of theelementary ¯ pp → ¯ ΛΛ presented in Tab. 1. With these as-sumptions we can obtain 2 (1) ¯ ΛΛ per second for p beam = . . GeV/ c . One day of data taking with 90% ef-fective run time at 1.64 GeV/ c will yield 15 · events,corresponding to a sample size two times as large as theone presented in Fig. 15. One week of data taking wouldalso enable measurements of polarisation and coplanarity.For the results presented in the right panel of Fig. 16,about 12000 Ξ − Ξ + pairs were generated for each value ofthe scaling factor ξ Ξ + . With the Phase One luminosity anda Ξ − Ξ + reconstruction efficiency of 5% (slightly smallerthan that of the elementary ¯ pp → ¯ Ξ + Ξ − presented inTab. 2), this requires a running time of about two months.The studies proposed here will benefit from measure-ments of the reference reaction pp → Y Y . However, asdiscussed in Section 5.1, such measurements already con-stitute an important part of the hyperon production pro-gramme and can, thanks to the predicted large productionrate, be completed in a very short time. The results fromour calculations illustrate that even with rather conserva-tive assumptions about luminosity, PANDA can provideunique and relevant information on the behaviour of an-tihyperons in nuclei already during Phase One.
Already in Section 5.1, it was concluded that PANDAwill be a strangeness factory. In combination with nu-clear targets, this opens up unique possibilities for pioneer-ing studies of the nuclear antihyperon potentials alreadyduring Phase One. In the future, when the luminosity isincreased, a unique programme for double- and possiblytriple strange hyperatom- and hypernuclear studies willfollow [245].
Figure 15: Average transverse momentum asymmetry α T (Eq.2) as a function of the longitudinal momentum asymmetryfor ΛΛ -pairs produced exclusively in 1.52 GeV/ c (left) and1.64 GeV/ c (right) ¯ p + Ne interactions. The different symbolsshow the GiBUU predictions for different scaling factors ξ Λ ofthe Λ -potential. Colour Transparency (CT) has mainly been studied in thehigh-energy regime, e.g. at Fermilab and HERA [246]. Atintermediate energies, some evidence was found by theCLAS collaboration for an onset of CT in exclusive mesonproduction with electron probes at momentum transfersof a few GeV [247, 248].Two-body hadron-nucleus reactions are also sensitiveto short-range nucleon–nucleon correlations [249]. Thesehave been studied experimentally for example in two-nucleon knockout reactions with proton beams at BNL[250, 251] and with electron beams at JLab [252, 253].It was found that inside ground-state nuclei, the short-range nucleon-nucleon interaction can give rise to cor-related nucleon pairs with large relative momenta but Σ − Λ pairs (left) and Ξ − Ξ + pairs (right) produced exclusively in1.64 GeV/ c p + Ne and 2.90 GeV/ c p + C interactions, re-spectively [245]. The different symbols show the GiBUU pre-dictions for different scaling factors for the antihyperon poten-tials. small centre-of-mass momenta, called short-range corre-lated (SRC) pairs.
Despite describing different physics phenomena, CT andSRC can be studied with similar probes and momentumregimes and with similar methods. Reactions with antipro-ton probes have the advantage that they give access tomesons that are unlikely to be produced with electronbeams, for example kaons.To establish the onset of CT in the intermediate energyregime indicated by CLAS, studies of e.g. exclusive mesonproduction in ¯ pp and ¯ pA have been suggested [254, 255].At large momentum transfer, a q ¯ q pair is more proba-ble to be in a small-size configuration than a qqq triplet due to combinatorics. Therefore, two-meson annihilationchannels provide a very promising search-ground for suchstudies. It is noteworthy that the main feature of the nu-clear target, i.e. the possibility of initial- and final stateinteractions with spectator nucleons, can be explored al-ready for the deuteron. The wave function of the deuteronis relatively well-known which allows for more robust the-oretical predictions. The simplest opportunity to studyCT is the d (¯ p, π − π ) p process at large momentum trans-fer in the elementary ¯ pn → π − π reaction [256]. The“golden” channel for nuclear transparency is considered tobe A (¯ p, J/ψ )( A − ∗ . During Phase One, it will be difficultto study charmonium production for heavy nuclei due tothe limited luminosity, but studies of the integrated crosssection with a deuteron target may be started. Calcula-tions of exclusive charmonium production d (¯ p, J/ψ ) n [257]predict a quite large cross section of ∼ nb at the quasi-free peak ( p lab = 4 . GeV/ c ).The same two-body antiproton reactions can be usedto study the decay of a short-range correlation after re-moval of one nucleon, for example ¯ p + A → h + h + N back + ( A − ∗ , where N back refers to a backward-goingnucleon [251]. In these reactions, it is possible to test thevalidity of factorisation of the cross section into the el-ementary cross section, the decay function, and the ab-sorption factor using different final states. Such tests incombination with analogous studies at JLab would con-tribute to detailed understanding of the dynamics of in-teractions with short-range correlations and high densityfluctuations in nuclei.In SRC studies, antiprotons give access to correlated pp and pn pairs without the necessity of identifying anddetermining the momentum of an outgoing neutron. In-stead, a struck neutron can be identified by reconstruct-ing processes like ¯ pn → π − π or ¯ pn → π + π − π − in thePANDA detector. The wave function of the SRC may in-clude the contribution of non-hadronic degrees of freedom.The simplest case is again provided by the deuteron wavefunction which may include the ∆ − ∆ component pre-dicted by meson-exchange model calculations [258] as wellas in the quark model [259]. The presence of the ∆ ++ − ∆ − configuration in the deuteron may be tested in the exclu-sive reaction ¯ pd → π − π − ∆ ++ [260]. In the PANDA mo-mentum range, the signal process due to the antiprotonannihilation on the valence ∆ − dominates over two-stepbackground processes. This is valid in a broad kinematicrange of the produced ∆ ++ also for ∆ − ∆ probabilitiesin the deuteron as low as ∼ . . At large beam momenta, PANDA can contribute withstudies of colour transparency and short-range correlatednucleon-nucleon pairs, and offers access to final stateswhich are difficult or unfeasible to study with electronor proton beams.The larger luminosities of the later stages of PANDAwill allow for more extensive studies of charmonium pro-duction A (¯ p, J/ψ )( A − ∗ reactions, both for deuterium targets and beyond. Exclusive studies of differential crosssections and J/ψ and ψ (cid:48) (2 S ) transparency ratios shed fur-ther light on colour transparency, as discussed in detail inRefs. [255, 261].The J/ψN absorption cross section is of particular in-terest for studies of Quark-Gluon Plasma in heavy-ion col-lisions [262].
The Standard Model of particle physics is highly success-ful in describing the strong interaction at high energies be-tween the fundamental constituents, i.e. the quarks andgluons. However, describing why and how these quarksand gluons form hadrons remains an open question. Themost prominent examples are the building blocks of mat-ter, i.e. the protons and the neutrons. Furthermore, it isa challenge to describe quantitatively how the effectiveforces between these composite objects emerge from firstprinciples: how do protons and neutrons form atomic nu-clei, and how do these form the macroscopic objects of ouruniverse, for example neutron stars?A central theme in strong interaction phenomena is thenon-Abelian nature of QCD, i.e. the self-coupling of theforce carriers. Self-coupling is present in all non-Abeliantheories such as gravity, but hadrons are so far the onlyobjects for which these effects can be studied in a con-trolled way in the laboratory.The PANDA experiment will provide the most ad-vanced and most multi-faceted facility for studies of differ-ent aspects of the strong interaction. PANDA will utilise abeam of antiprotons: a unique and highly versatile probefor hadron physics. The beam energy provided by theHESR storage ring is optimised to shed light on the veryregime where quarks form hadrons. Combined with a near4 π multipurpose detector, PANDA will offer the broadesthadron physics programme of any existing or planned ex-periment in the world.The PANDA physics programme will benefit from therecent theoretical developments (Lattice QCD, effectivefield theory, Dyson-Schwinger approach, AdS/QFT, Lightfront holographic QCD, etc.), but also provide guidancefrom data to the construction of new theoretical and phe-nomenological tools, as well as refinements of the existingones. The close collaboration between theory and experi-ment will hence be mutually beneficial and has potentialto give new insights in the dynamics of non-linear inter-acting systems on a quantum scale.In this paper, we have discussed the potential ofPANDA during the first phase of data collection, PhaseOne, when the luminosity will be ≈
20 times lower thanthe FAIR design value and the experimental setup willbe slightly reduced. The four main physics domains ofPANDA – nucleon structure, strangeness physics, charmand exotics, and hadrons in nuclei – has been discussedwithin the context of Phase One. Highlights have beenoutlined and the potential for PANDA to push the fron-tiers beyond state of the art was demonstrated for se-lected examples. PANDA is the only experiment that can investigate certain aspects of nucleon structure, performline-shape measurements of non-vector charmonium-likestates, study multistrange hyperons at a large scale andantihyperons in nuclei. Furthermore, it offers better pre-cision and complementary approaches to topics like time-like form factors, light hadron spectroscopy and colourtransparency. In later phases of the PANDA experiment,the full setup and the design luminosity enable an evenwider programme that also includes open-charm produc-tion, triple-strange hyperon physics, hyperatom and hy-pernuclear physics and searches for physics beyond theStandard Model e.g. through hyperon decays.
Acknowledgement
We acknowledge the support of the Theory AdvisoryGroup (ThAG) of PANDA and we value the various dis-cussions that took place with the ThAG sharpening thephysics programme of PANDA. We appreciate the com-ments and feedback we received from Gunnar Bali, NoraBrambilla, Stan Brodsky, Alexei Larionov, Horst Lenske,Stefan Leupold, Ulf Meißner, Simone Pacetti, Mark Strik-man, and Lech Szymanowski.We acknowledge financial support from the BhabhaAtomic Research Centre (BARC) and the Indian Insti-tute of Technology Bombay, India; the Bundesministeriumfür Bildung und Forschung (BMBF), Germany; the Carl-Zeiss-Stiftung 21-0563-2.8/122/1 and 21-0563-2.8/131/1,Mainz, Germany; the CNRS/IN2P3 and the UniversitéParis-Sud, France; the Czech Ministry (MEYS) grantsLM2015049, CZ.02.1.01/0.0/0.0/16 and 013/0001677,the Deutsche Forschungsgemeinschaft (DFG), Germany;the Deutscher Akademischer Austauschdienst (DAAD),Germany; the European Union’s Horizon 2020 re-search and innovation programme under grant agree-ment No 824093. the Forschungszentrum Jülich, Ger-many; the Gesellschaft für Schwerionenforschung GmbH(GSI), Darmstadt, Germany; the Helmholtz-GemeinschaftDeutscher Forschungszentren (HGF), Germany; the IN-TAS, European Commission funding; the Institute of HighEnergy Physics (IHEP) and the Chinese Academy of Sci-ences, Beijing, China; the Istituto Nazionale di Fisica Nu-cleare (INFN), Italy; the Ministerio de Educacion y Cien-cia (MEC) under grant FPA2006-12120-C03-02; the Pol-ish Ministry of Science and Higher Education (MNiSW)grant No. 2593/7, PR UE/2012/2, and the National Sci-ence Centre (NCN) DEC-2013/09/N/ST2/02180, Poland;the State Atomic Energy Corporation Rosatom, Na-tional Research Center Kurchatov Institute, Russia; theSchweizerischer Nationalfonds zur Förderung der Wis-senschaftlichen Forschung (SNF), Swiss; the Science andTechnology Facilities Council (STFC), British fundingagency, Great Britain; the Scientific and Technologi-cal Research Council of Turkey (TUBITAK) under theGrant No. 119F094 the Stefan Meyer Institut für Sub-atomare Physik and the Österreichische Akademie derWissenschaften, Wien, Austria; the Swedish ResearchCouncil and the Knut and Alice Wallenberg Foundation,Sweden. References
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