P. Novella

First proof of topological signature in high pressure xenon gas with electroluminescence amplification

A bstractThe NEXT experiment aims to observe the neutrinoless double beta decay of 136Xe in a high-pressure xenon gas TPC using electroluminescence (EL) to amplify the signal from ionization. One of the main advantages of this technology is the possibility to reconstruct the topology of events with energies close to Qββ. This paper presents the first demonstration that the topology provides extra handles to reject background events using data obtained with the NEXT-DEMO prototype.Single electrons resulting from the interactions of 22Na 1275 keV gammas and electronpositron pairs produced by conversions of gammas from the 228Th decay chain were used to represent the background and the signal in a double beta decay. These data were used to develop algorithms for the reconstruction of tracks and the identification of the energy deposited at the end-points, providing an extra background rejection factor of 24.3 ± 1.4 (stat.)%, while maintaining an efficiency of 66.7 ± 1.% for signal events.

Large-angle production of charged pions with 3-12.9 GeV/c incident protons on nuclear targets

M.G. Catanesi, E. Radicioni, R. Edgecock, M. Ellis, ∗ F.J.P. Soler, C. Gößling, S. Bunyatov, A. Krasnoperov, B. Popov, † V. Serdiouk, V. Tereschenko, E. Di Capua, G. Vidal–Sitjes, ‡ A. Artamonov, § S. Giani, S. Gilardoni, P. Gorbunov, § A. Grant, A. Grossheim, ¶ A. Ivanchenko, ∗∗ V. Ivanchenko, †† A. Kayis-Topaksu, ‡‡ J. Panman, I. Papadopoulos, E. Tcherniaev, I. Tsukerman, § R. Veenhof, C. Wiebusch, §§ P. Zucchelli, ¶¶ A. Blondel, S. Borghi, M.C. Morone, ∗∗∗ G. Prior, † † † R. Schroeter, C. Meurer, U. Gastaldi, G. B. Mills, ‡ ‡ ‡ J.S. Graulich, §§§ G. Grégoire, M. Bonesini, ¶¶¶ F. Ferri, M. Kirsanov, A. Bagulya, V. Grichine, N. Polukhina, V. Palladino, L. Coney, ‡ ‡ ‡ D. Schmitz, ‡ ‡ ‡ G. Barr, A. De Santo, F. Bobisut, D. Gibin, A. Guglielmi, M. Mezzetto, J. Dumarchez, U. Dore, D. Orestano, F. Pastore, A. Tonazzo, L. Tortora, C. Booth, L. Howlett, G. Skoro, M. Bogomilov, M. Chizhov, D. Kolev, R. Tsenov, S. Piperov, P. Temnikov, M. Apollonio, P. Chimenti, G. Giannini, J. Burguet–Castell, A. Cervera–Villanueva, J.J. Gómez–Cadenas, J. Mart́ın–Albo, P. Novella, M. Sorel, and A. Tornero (HARP Collaboration)

Measurement of the production cross-sections of pi(+/-) in p-C and pi(+/-)-C interactions at 12 GeV/c

The results of the measurements of the double-differential production cross-sections of pions, dσ/dpdΩ, in p-C and π-C interactions using the forward spectrometer of the HARP experiment are presented. The incident particles are 12 GeV/c protons and charged pions directed onto a carbon target with a thickness of 5% of a nuclear interaction length. For p-C interactions the analysis is performed using 100 035 reconstructed secondary tracks, while the corresponding numbers of tracks for π-C and π-C analyses are 106 534 and 10 122 respectively. Cross-section results are presented in the kinematic range 0.5 GeV/c ≤ pπ < 8 GeV/c and 30 mrad ≤ θπ < 240 mrad in the laboratory frame. The measured cross-sections have a direct impact on the precise calculation of atmospheric neutrino fluxes and on the improved reliability of extensive air shower simulations by reducing the uncertainties of hadronic interaction models in the low energy range. HARP collaboration M.G. Catanesi, E. Radicioni Università degli Studi e Sezione INFN, Bari, Italy R. Edgecock, M. Ellis, S. Robbins, F.J.P. Soler Rutherford Appleton Laboratory, Chilton, Didcot, UK C. Gößling Institut für Physik, Universität Dortmund, Germany S. Bunyatov, A. Krasnoperov, B. Popov, V. Tereshchenko Joint Institute for Nuclear Research, JINR Dubna, Russia E. Di Capua, G. Vidal–Sitjes Università degli Studi e Sezione INFN, Ferrara, Italy A. Artamonov, S. Giani, S. Gilardoni, P. Gorbunov, A. Grant, A. Grossheim, P. Gruber, V. Ivanchenko, A. Kayis-Topaksu, J. Panman, I. Papadopoulos, E. Tcherniaev, I. Tsukerman, R. Veenhof, C. Wiebusch, P. Zucchelli CERN, Geneva, Switzerland A. Blondel, S. Borghi, M. Campanelli, M.C. Morone, G. Prior, R. Schroeter Section de Physique, Université de Genève, Switzerland R. Engel, C. Meurer Forschungszentrum Karlsruhe, Institut für Kernphysik, Karlsruhe, Germany I. Kato University of Kyoto, Japan U. Gastaldi Laboratori Nazionali di Legnaro dell’ INFN, Legnaro, Italy G. B. Mills Los Alamos National Laboratory, Los Alamos, USA J.S. Graulich, G. Grégoire Institut de Physique Nucléaire, UCL, Louvain-la-Neuve, Belgium M. Bonesini, F. Ferri Università degli Studi e Sezione INFN, Milano, Italy M. Kirsanov Institute for Nuclear Research, Moscow, Russia A. Bagulya, V. Grichine, N. Polukhina P. N. Lebedev Institute of Physics (FIAN), Russian Academy of Sciences, Moscow, Russia V. Palladino Università “Federico II” e Sezione INFN, Napoli, Italy L. Coney, D. Schmitz Columbia University, New York, USA G. Barr, A. De Santo, C. Pattison, K. Zuber Nuclear and Astrophysics Laboratory, University of Oxford, UK F. Bobisut, D. Gibin, A. Guglielmi, M. Mezzetto Università degli Studi e Sezione INFN, Padova, Italy J. Dumarchez, F. Vannucci LPNHE, Universités de Paris VI et VII, Paris, France U. Dore Università “La Sapienza” e Sezione INFN Roma I, Roma, Italy D. Orestano, F. Pastore, A. Tonazzo, L. Tortora Università degli Studi e Sezione INFN Roma III, Roma, Italy C. Booth, L. Howlett Dept. of Physics, University of Sheffield, UK M. Bogomilov, M. Chizhov, D. Kolev, R. Tsenov Faculty of Physics, St. Kliment Ohridski University, Sofia, Bulgaria S. Piperov, P. Temnikov Institute for Nuclear Research and Nuclear Energy, Academy of Sciences, Sofia, Bulgaria M. Apollonio, P. Chimenti, G. Giannini, G. Santin Università degli Studi e Sezione INFN, Trieste, Italy J. Burguet–Castell, A. Cervera–Villanueva, J.J. Gómez–Cadenas, J. Mart́ın–Albo, P. Novella, M. Sorel Instituto de F́ısica Corpuscular, IFIC, CSIC and Universidad de Valencia, Spain Now at FNAL, Batavia, Illinois, USA. Jointly appointed by Nuclear and Astrophysics Laboratory, University of Oxford, UK. Now at Codian Ltd., Langley, Slough, UK. Now at University of Glasgow, UK. Also supported by LPNHE, Universités de Paris VI et VII, Paris, France. Now at Imperial College, University of London, UK. ITEP, Moscow, Russian Federation. Permanently at Instituto de F́ısica de Cantabria, Univ. de Cantabria, Santander, Spain. Now at SpinX Technologies, Geneva, Switzerland. Now at TRIUMF, Vancouver, Canada. Now at University of St. Gallen, Switzerland. On leave of absence from Ecoanalitica, Moscow State University, Moscow, Russia. Now at Çukurova University, Adana, Turkey. Now at III Phys. Inst. B, RWTH Aachen, Aachen, Germany. On leave of absence from INFN, Sezione di Ferrara, Italy. Now at CERN, Geneva, Switzerland. Now at Univerity of Rome Tor Vergata, Italy. Now at Lawrence Berkeley National Laboratory, Berkeley, California, USA. K2K Collaboration. MiniBooNE Collaboration. Now at Section de Physique, Université de Genève, Switzerland, Switzerland. Now at Royal Holloway, University of London, UK. Now at University of Sussex, Brighton, UK. Now at ESA/ESTEC, Noordwijk, The Netherlands.

Large-angle production of charged pions with incident pion beams on nuclear targets

We gratefully acknowledge the help and support of the PS beam staff and of the numerous technical collaborators who contributed to the detector design, construction, commissioning and operation. In particular, we would like to thank G. Barichello, R. Brocard, K. Burin, V. Carassiti, F. Chignoli, D. Conventi, G. Decreuse, M. Delattre, C. Detraz, A. Domeniconi, M. Dwuznik, F. Evangelisti, B. Friend, A. Iaciofano, I. Krasin, D. Lacroix, J.-C. Legrand, M. Lobello, M. Lollo, J. Loquet, F. Marinilli, J. Mulon, L. Musa, R. Nicholson, A. Pepato, P. Petev, X. Pons, I. Rusinov, M. Scandurra, E. Usenko, and R. van der Vlugt, for their support in the construction of the detector. The collaboration acknowledges the major contributions and advice of M. Baldo-Ceolin, L. Linssen, M.T. Muciaccia and A. Pullia during the construction of the experiment. The collaboration is indebted to V. Ableev, P. Arce, F. Bergsma, P. Binko, E. Boter, C. Buttar, M. Calvi, M. Campanelli, C. Cavion, A. Chukanov, A. De Min, M. Doucet, D. Dullmann, R. Engel, V. Ermilova, W. Flegel, P. Gruber, Y. Hayato, P. Hodgson, A. Ichikawa, I. Kato, O. Klimov, T. Kobayashi, D. Kustov, M. Laveder, M. Mass, H. Meinhard, T. Nakaya, K. Nishikawa, M. Paganoni, F. Paleari, M. Pasquali, J. Pasternak, C. Pattison, M. Placentino, S. Robbins, G. Santin, V. Serdiouk, S. Simone, A. Tornero, S. Troquereau, S. Ueda, A. Valassi, F. Vannucci and K. Zuber for their contributions to the experiment and to P. Dini for help in MC production. We acknowledge the contributions of V. Ammosov, G. Chelkov, D. Dedovich, F. Dydak, M. Gostkin, A. Guskov, D. Khartchenko, V. Koreshev, Z. Kroumchtein, I. Nefedov, A. Semak, J. Wotschack, V. Zaets and A. Zhemchugov to the work described in this paper. The experiment was made possible by grants from the Institut Interuniversitaire des Sciences Nucleaires and the Interuniversitair Instituut voor Kernwetenschappen (Belgium), Ministerio de Educacion y Ciencia, Grant FPA2003-06921-c02-02 and Generalitat Valenciana, grant GV00-054-1, CERN (Geneva, Switzerland), the German Bundesministerium fur Bildung und Forschung (Germany), the Istituto Nazionale di Fisica Nucleare (Italy), INR RAS (Moscow), the Russian Foundation for Basic Research (grant 08-02-00018) and the Particle Physics and Astronomy Research Council (UK). We gratefully acknowledge their support. This work was supported in part by the Swiss National Science Foundation and the Swiss Agency for Development and Cooperation in the framework of the programme SCOPES - Scientific co-operation between Eastern Europe and Switzerland.

Background rejection in NEXT using deep neural networks

We investigate the potential of using deep learning techniques to reject background events in searches for neutrinoless double beta decay with high pressure xenon time projection chambers capable of detailed track reconstruction. The differences in the topological signatures of background and signal events can be learned by deep neural networks via training over many thousands of events. These networks can then be used to classify further events as signal or background, providing an additional background rejection factor at an acceptable loss of efficiency. The networks trained in this study performed better than previous methods developed based on the use of the same topological signatures by a factor of 1.2 to 1.6, and there is potential for further improvement.

Forward production of charged pions with incident protons on nuclear targets at the CERN Proton Synchrotron

Measurements of the double-differential π production cross-section in the range of momentum 0.5 GeV/c ≤ p ≤ 8.0 GeV/c and angle 0.025 rad ≤ θ ≤ 0.25 rad in collisions of protons on beryllium, carbon, nitrogen, oxygen, aluminium, copper, tin, tantalum and lead are presented. The data were taken with the large acceptance HARP detector in the T9 beam line of the CERN PS. Incident particles were identified by an elaborate system of beam detectors. Thin targets of 5% of a nuclear interaction length were used. The tracking and identification of the produced particles were performed using the forward system of the HARP experiment. Results are obtained for the double-differential cross-sections dσ/dpdΩ mainly at four incident proton beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c and 12 GeV/c). Measurements are compared with the GEANT4 and MARS Monte Carlo generators. A global parametrization is provided as an approximation of all the collected datasets which can serve as a tool for quick yields estimates.

Absolute momentum calibration of the HARP TPC

In the HARP experiment the large-angle spectrometer is using a cylindrical TPC as main tracking and particle identification detector. The momentum scale of reconstructed tracks in the TPC is the most important systematic error for the majority of kinematic bins used for the HARP measurements of the double-differential production cross-section of charged pions in proton interactions on nuclear targets at large angle. The HARP TPC operated with a number of hardware shortfalls and operational mistakes. Thus it was important to control and characterize its momentum calibration. While it was not possible to enter a direct particle beam into the sensitive volume of the TPC to calibrate the detector, a set of physical processes and detector properties were exploited to achieve a precise calibration of the apparatus. In the following we recall the main issues concerning the momentum measurement in the HARP TPC, and describe the crosschecks made to validate the momentum scale. As a conclusion, this analysis demonstrates that the measurement of momentum is correct within the published precision of 3%.

Forward production of charged pions with incident pi(+/-) on nuclear targets measured at the CERN PS

Measurements of the double-differential π production cross-section in the range of momentum 0.5 GeV/c ≤ p ≤ 8.0 GeV/c and angle 0.025 rad ≤ θ ≤ 0.25 rad in interactions of charged pions on beryllium, carbon, aluminium, copper, tin, tantalum and lead are presented. These data represent the first experimental campaign to systematically measure forward pion hadroproduction. The data were taken with the large acceptance HARP detector in the T9 beam line of the CERN PS. Incident particles, impinging on a 5% nuclear interaction length target, were identified by an elaborate system of beam detectors. The tracking and identification of the produced particles was performed using the forward spectrometer of the HARP detector. Results are obtained for the doubledifferential cross-sections dσ/dpdΩ mainly at four incident pion beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c and 12 GeV/c). The measurements are compared with the GEANT4 and MARS Monte Carlo simulation.

Application and performance of an ML-EM algorithm in NEXT

The goal of the NEXT experiment is the observation of neutrinoless double beta decay in 136Xe using a gaseous xenon TPC with electroluminescent amplification and specialized photodetector arrays for calorimetry and tracking. The NEXT Collaboration is exploring a number of reconstruction algorithms to exploit the full potential of the detector. This paper describes one of them: the Maximum Likelihood Expectation Maximization (ML-EM) method, a generic iterative algorithm to find maximum-likelihood estimates of parameters that has been applied to solve many different types of complex inverse problems. In particular, we discuss a bi-dimensional version of the method in which the photosensor signals integrated over time are used to reconstruct a transverse projection of the event. First results show that, when applied to detector simulation data, the algorithm achieves nearly optimal energy resolution (better than 0.5% FWHM at the Q value of 136Xe) for events distributed over the full active volume of the TPC.

Measurements of forward proton production with incident protons and charged pions on nuclear targets at the CERN Proton Synchroton

Measurements of the double-differential proton production cross-section dσ/dpdΩ in the range of momentum 0.5 GeV/c ≤ p < 8.0 GeV/c and angle 0.05 rad ≤ θ < 0.25 rad in collisions of charged pions and protons on beryllium, carbon, aluminium, copper, tin, tantalum and lead are presented. The data were taken with the large acceptance HARP detector in the T9 beam line of the CERN Proton Synchrotron. Incident particles were identified by an elaborate system of beam detectors and impinged on a target of 5% of a nuclear interaction length. The tracking and identification of the produced particles was performed using the forward spectrometer of the HARP experiment. Results are obtained for the double-differential cross-sections mainly at four incident beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c and 12 GeV/c). Measurements are compared with predictions of the GEANT4 and MARS Monte Carlo generators.