Search for a resonance decaying into WZ boson pairs in p p ¯ collisions
aa r X i v : . [ h e p - e x ] F e b Search for a resonance decaying into
W Z boson pairs in p ¯ p collisions V.M. Abazov , B. Abbott , M. Abolins , B.S. Acharya , M. Adams , T. Adams , E. Aguilo , M. Ahsan ,G.D. Alexeev , G. Alkhazov , A. Alton ,a , G. Alverson , G.A. Alves , L.S. Ancu , M. Aoki , Y. Arnoud ,M. Arov , A. Askew , B. ˚Asman , O. Atramentov ,b , C. Avila , J. BackusMayes , F. Badaud , L. Bagby ,B. Baldin , D.V. Bandurin , S. Banerjee , E. Barberis , A.-F. Barfuss , P. Baringer , J. Barreto ,J.F. Bartlett , U. Bassler , D. Bauer , S. Beale , A. Bean , M. Begalli , M. Begel , C. Belanger-Champagne ,L. Bellantoni , J.A. Benitez , S.B. Beri , G. Bernardi , R. Bernhard , I. Bertram , M. Besan¸con ,R. Beuselinck , V.A. Bezzubov , P.C. Bhat , V. Bhatnagar , G. Blazey , S. Blessing , K. Bloom ,A. Boehnlein , D. Boline , T.A. Bolton , E.E. Boos , G. Borissov , T. Bose , A. Brandt , R. Brock ,G. Brooijmans , A. Bross , D. Brown , X.B. Bu , D. Buchholz , M. Buehler , V. Buescher , V. Bunichev ,S. Burdin ,c , T.H. Burnett , C.P. Buszello , P. Calfayan , B. Calpas , S. Calvet , E. Camacho-P´erez ,J. Cammin , M.A. Carrasco-Lizarraga , E. Carrera , W. Carvalho , B.C.K. Casey , H. Castilla-Valdez ,S. Chakrabarti , D. Chakraborty , K.M. Chan , A. Chandra , E. Cheu , S. Chevalier-Th´ery , D.K. Cho ,S.W. Cho , S. Choi , B. Choudhary , T. Christoudias , S. Cihangir , D. Claes , J. Clutter , M. Cooke ,W.E. Cooper , M. Corcoran , F. Couderc , M.-C. Cousinou , D. Cutts , M. ´Cwiok , A. Das , G. Davies ,K. De , S.J. de Jong , E. De La Cruz-Burelo , K. DeVaughan , F. D´eliot , M. Demarteau , R. Demina ,D. Denisov , S.P. Denisov , S. Desai , H.T. Diehl , M. Diesburg , A. Dominguez , T. Dorland , A. Dubey ,L.V. Dudko , L. Duflot , D. Duggan , A. Duperrin , S. Dutt , A. Dyshkant , M. Eads , D. Edmunds ,J. Ellison , V.D. Elvira , Y. Enari , S. Eno , H. Evans , A. Evdokimov , V.N. Evdokimov , G. Facini ,A.V. Ferapontov , T. Ferbel , , F. Fiedler , F. Filthaut , W. Fisher , H.E. Fisk , M. Fortner , H. Fox ,S. Fuess , T. Gadfort , C.F. Galea , A. Garcia-Bellido , V. Gavrilov , P. Gay , W. Geist , W. Geng , ,D. Gerbaudo , C.E. Gerber , Y. Gershtein ,b , D. Gillberg , G. Ginther , , G. Golovanov , B. G´omez ,A. Goussiou , P.D. Grannis , S. Greder , H. Greenlee , Z.D. Greenwood , E.M. Gregores , G. Grenier ,Ph. Gris , J.-F. Grivaz , A. Grohsjean , S. Gr¨unendahl , M.W. Gr¨unewald , F. Guo , J. Guo ,G. Gutierrez , P. Gutierrez , A. Haas ,d , P. Haefner , S. Hagopian , J. Haley , I. Hall , R.E. Hall , L. Han ,K. Harder , A. Harel , J.M. Hauptman , J. Hays , T. Hebbeker , D. Hedin , J.G. Hegeman , A.P. Heinson ,U. Heintz , C. Hensel , I. Heredia-De La Cruz , K. Herner , G. Hesketh , M.D. Hildreth , R. Hirosky ,T. Hoang , J.D. Hobbs , B. Hoeneisen , M. Hohlfeld , S. Hossain , P. Houben , Y. Hu , Z. Hubacek ,N. Huske , V. Hynek , I. Iashvili , R. Illingworth , A.S. Ito , S. Jabeen , M. Jaffr´e , S. Jain , K. Jakobs ,D. Jamin , R. Jesik , K. Johns , C. Johnson , M. Johnson , D. Johnston , A. Jonckheere , P. Jonsson ,A. Juste , K. Kaadze , E. Kajfasz , D. Karmanov , P.A. Kasper , I. Katsanos , V. Kaushik , R. Kehoe ,S. Kermiche , N. Khalatyan , A. Khanov , A. Kharchilava , Y.N. Kharzheev , D. Khatidze , M.H. Kirby ,M. Kirsch , J.M. Kohli , A.V. Kozelov , J. Kraus , A. Kumar , A. Kupco , T. Kurˇca , V.A. Kuzmin ,J. Kvita , F. Lacroix , D. Lam , S. Lammers , G. Landsberg , P. Lebrun , H.S. Lee , W.M. Lee , A. Leflat ,J. Lellouch , L. Li , Q.Z. Li , S.M. Lietti , J.K. Lim , D. Lincoln , J. Linnemann , V.V. Lipaev , R. Lipton ,Y. Liu , Z. Liu , A. Lobodenko , M. Lokajicek , P. Love , H.J. Lubatti , R. Luna-Garcia ,e , A.L. Lyon ,A.K.A. Maciel , D. Mackin , P. M¨attig , R. Maga˜na-Villalba , P.K. Mal , S. Malik , V.L. Malyshev ,Y. Maravin , B. Martin , J. Mart´ınez-Ortega , R. McCarthy , C.L. McGivern , M.M. Meijer ,A. Melnitchouk , L. Mendoza , D. Menezes , P.G. Mercadante , M. Merkin , A. Meyer , J. Meyer ,N.K. Mondal , R.W. Moore , T. Moulik , G.S. Muanza , M. Mulhearn , O. Mundal , L. Mundim , E. Nagy ,M. Naimuddin , M. Narain , R. Nayyar , H.A. Neal , J.P. Negret , P. Neustroev , H. Nilsen , H. Nogima ,S.F. Novaes , T. Nunnemann , G. Obrant , D. Onoprienko , J. Orduna , N. Osman , J. Osta , R. Otec ,G.J. Otero y Garz´on , M. Owen , M. Padilla , P. Padley , M. Pangilinan , N. Parashar , V. Parihar ,S.-J. Park , S.K. Park , J. Parsons , R. Partridge , N. Parua , A. Patwa , B. Penning , M. Perfilov ,K. Peters , Y. Peters , P. P´etroff , R. Piegaia , J. Piper , M.-A. Pleier , P.L.M. Podesta-Lerma ,f ,V.M. Podstavkov , Y. Pogorelov , M.-E. Pol , P. Polozov , A.V. Popov , M. Prewitt , S. Protopopescu ,J. Qian , A. Quadt , B. Quinn , M.S. Rangel , K. Ranjan , P.N. Ratoff , I. Razumov , P. Renkel , P. Rich ,M. Rijssenbeek , I. Ripp-Baudot , F. Rizatdinova , S. Robinson , M. Rominsky , C. Royon , P. Rubinov ,R. Ruchti , G. Safronov , G. Sajot , A. S´anchez-Hern´andez , M.P. Sanders , B. Sanghi , G. Savage ,L. Sawyer , T. Scanlon , D. Schaile , R.D. Schamberger , Y. Scheglov , H. Schellman , T. Schliephake ,S. Schlobohm , C. Schwanenberger , R. Schwienhorst , J. Sekaric , H. Severini , E. Shabalina , M. Shamim ,V. Shary , A.A. Shchukin , R.K. Shivpuri , V. Simak , V. Sirotenko , P. Skubic , P. Slattery , D. Smirnov ,G.R. Snow , J. Snow , S. Snyder , S. S¨oldner-Rembold , L. Sonnenschein , A. Sopczak , M. Sosebee ,K. Soustruznik , B. Spurlock , J. Stark , V. Stolin , D.A. Stoyanova , J. Strandberg , M.A. Strang ,E. Strauss , M. Strauss , R. Str¨ohmer , D. Strom , L. Stutte , S. Sumowidagdo , P. Svoisky , M. Takahashi ,A. Tanasijczuk , W. Taylor , B. Tiller , M. Titov , V.V. Tokmenin , I. Torchiani , D. Tsybychev ,B. Tuchming , C. Tully , P.M. Tuts , R. Unalan , L. Uvarov , S. Uvarov , S. Uzunyan , P.J. van den Berg ,R. Van Kooten , W.M. van Leeuwen , N. Varelas , E.W. Varnes , I.A. Vasilyev , P. Verdier ,L.S. Vertogradov , M. Verzocchi , M. Vesterinen , D. Vilanova , P. Vint , P. Vokac , R. Wagner ,H.D. Wahl , M.H.L.S. Wang , J. Warchol , G. Watts , M. Wayne , G. Weber , M. Weber ,g , A. Wenger ,h ,M. Wetstein , A. White , D. Wicke , M.R.J. Williams , G.W. Wilson , S.J. Wimpenny , M. Wobisch ,D.R. Wood , T.R. Wyatt , Y. Xie , C. Xu , S. Yacoob , R. Yamada , W.-C. Yang , T. Yasuda ,Y.A. Yatsunenko , Z. Ye , H. Yin , K. Yip , H.D. Yoo , S.W. Youn , J. Yu , C. Zeitnitz , S. Zelitch ,T. Zhao , B. Zhou , J. Zhu , M. Zielinski , D. Zieminska , L. Zivkovic , V. Zutshi , and E.G. Zverev (The DØ Collaboration) Universidad de Buenos Aires, Buenos Aires, Argentina LAFEX, Centro Brasileiro de Pesquisas F´ısicas, Rio de Janeiro, Brazil Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil Universidade Federal do ABC, Santo Andr´e, Brazil Instituto de F´ısica Te´orica, Universidade Estadual Paulista, S˜ao Paulo, Brazil University of Alberta, Edmonton, Alberta, Canada; Simon Fraser University,Burnaby, British Columbia, Canada; York University, Toronto,Ontario, Canada and McGill University, Montreal, Quebec, Canada University of Science and Technology of China, Hefei, People’s Republic of China Universidad de los Andes, Bogot´a, Colombia Center for Particle Physics, Charles University,Faculty of Mathematics and Physics, Prague, Czech Republic Czech Technical University in Prague, Prague, Czech Republic Center for Particle Physics, Institute of Physics,Academy of Sciences of the Czech Republic, Prague, Czech Republic Universidad San Francisco de Quito, Quito, Ecuador LPC, Universit´e Blaise Pascal, CNRS/IN2P3, Clermont, France LPSC, Universit´e Joseph Fourier Grenoble 1, CNRS/IN2P3,Institut National Polytechnique de Grenoble, Grenoble, France CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France LAL, Universit´e Paris-Sud, IN2P3/CNRS, Orsay, France LPNHE, IN2P3/CNRS, Universit´es Paris VI and VII, Paris, France CEA, Irfu, SPP, Saclay, France IPHC, Universit´e de Strasbourg, CNRS/IN2P3, Strasbourg, France IPNL, Universit´e Lyon 1, CNRS/IN2P3, Villeurbanne, France and Universit´e de Lyon, Lyon, France III. Physikalisches Institut A, RWTH Aachen University, Aachen, Germany Physikalisches Institut, Universit¨at Bonn, Bonn, Germany Physikalisches Institut, Universit¨at Freiburg, Freiburg, Germany II. Physikalisches Institut, Georg-August-Universit¨at G¨ottingen, G¨ottingen, Germany Institut f¨ur Physik, Universit¨at Mainz, Mainz, Germany Ludwig-Maximilians-Universit¨at M¨unchen, M¨unchen, Germany Fachbereich Physik, University of Wuppertal, Wuppertal, Germany Panjab University, Chandigarh, India Delhi University, Delhi, India Tata Institute of Fundamental Research, Mumbai, India University College Dublin, Dublin, Ireland Korea Detector Laboratory, Korea University, Seoul, Korea SungKyunKwan University, Suwon, Korea CINVESTAV, Mexico City, Mexico FOM-Institute NIKHEF and University of Amsterdam/NIKHEF, Amsterdam, The Netherlands Radboud University Nijmegen/NIKHEF, Nijmegen, The Netherlands Joint Institute for Nuclear Research, Dubna, Russia Institute for Theoretical and Experimental Physics, Moscow, Russia Moscow State University, Moscow, Russia Institute for High Energy Physics, Protvino, Russia Petersburg Nuclear Physics Institute, St. Petersburg, Russia Stockholm University, Stockholm, Sweden, and Uppsala University, Uppsala, Sweden Lancaster University, Lancaster, United Kingdom Imperial College London, London SW7 2AZ, United Kingdom The University of Manchester, Manchester M13 9PL, United Kingdom University of Arizona, Tucson, Arizona 85721, USA California State University, Fresno, California 93740, USA University of California, Riverside, California 92521, USA Florida State University, Tallahassee, Florida 32306, USA Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA University of Illinois at Chicago, Chicago, Illinois 60607, USA Northern Illinois University, DeKalb, Illinois 60115, USA Northwestern University, Evanston, Illinois 60208, USA Indiana University, Bloomington, Indiana 47405, USA University of Notre Dame, Notre Dame, Indiana 46556, USA Purdue University Calumet, Hammond, Indiana 46323, USA Iowa State University, Ames, Iowa 50011, USA University of Kansas, Lawrence, Kansas 66045, USA Kansas State University, Manhattan, Kansas 66506, USA Louisiana Tech University, Ruston, Louisiana 71272, USA University of Maryland, College Park, Maryland 20742, USA Boston University, Boston, Massachusetts 02215, USA Northeastern University, Boston, Massachusetts 02115, USA University of Michigan, Ann Arbor, Michigan 48109, USA Michigan State University, East Lansing, Michigan 48824, USA University of Mississippi, University, Mississippi 38677, USA University of Nebraska, Lincoln, Nebraska 68588, USA Princeton University, Princeton, New Jersey 08544, USA State University of New York, Buffalo, New York 14260, USA Columbia University, New York, New York 10027, USA University of Rochester, Rochester, New York 14627, USA State University of New York, Stony Brook, New York 11794, USA Brookhaven National Laboratory, Upton, New York 11973, USA Langston University, Langston, Oklahoma 73050, USA University of Oklahoma, Norman, Oklahoma 73019, USA Oklahoma State University, Stillwater, Oklahoma 74078, USA Brown University, Providence, Rhode Island 02912, USA University of Texas, Arlington, Texas 76019, USA Southern Methodist University, Dallas, Texas 75275, USA Rice University, Houston, Texas 77005, USA University of Virginia, Charlottesville, Virginia 22901, USA and University of Washington, Seattle, Washington 98195, USA
We present the first search for an electrically charged resonance W ′ decaying to a W Z boson pairusing 4.1 fb − of integrated luminosity collected with the D0 detector at the Fermilab Tevatron p ¯ p collider. The W Z pairs are reconstructed through their decays into three charged leptons ( ℓ = e, µ ).A total of 9 data events is observed in good agreement with the background prediction. We set95% C.L. limits on the W ′ W Z coupling and on the W ′ production cross section multiplied by thebranching fractions. We also exclude W ′ masses between 188 and 520 GeV within a simple extensionof the standard model and set the most restrictive limits to date on low-scale technicolor models. PACS numbers: 12.60.Nz, 12.60.Cn, 13.85.Rm, 14.70.Pw
The standard model (SM) of particle physics is widelybelieved to be a low energy approximation of a more fun-damental theory of elementary particles and their inter-actions. Many extensions of the SM, such as the sequen-tial standard model (SSM) [9], extra dimensions [10], lit-tle Higgs [11], and technicolor [12] models, predict newheavy W ′ resonances decaying to a pair of electroweak W and Z bosons. Some models [10–12] also offer an al-ternative to the SM mechanism of electroweak symmetry breaking. Thus, the observation of resonant W Z bosonproduction would not only manifest new physics beyondthe SM, but also could yield an insight into the origin ofmass.This Letter describes the first search for a heavycharged boson, referred to as the W ′ , decaying to W and Z bosons. The CDF and D0 collaborations have searchedfor a W ′ decaying to fermions [13–15]. Current limits ex-clude W ′ with masses < ∼ W ′ → W Z decay isfully suppressed. Thus, our search is complementary tothe previous studies.In technicolor, particles such as ρ T and a T have narrowwidths and can decay to W Z bosons. The experimentalsignature of these particles is therefore similar to that of a W ′ . We will interpret the results of our search within thelow-scale technicolor model (LSTC), where the massesof ρ T and a T are predicted to be below 500 GeV, wellwithin the energy reach of the Tevatron. Since ρ T and a T have almost the same mass we refer to them collectivelyas ρ T . The branching fraction for ρ T → W Z dependsstrongly on the relative masses of the technipion, M ( π T ),and technirho, M ( ρ T ). The D0 collaboration searchedpreviously for technicolor in the W π T → W + jets finalstate [16], which is one of the major decay channels forlight technipions. In this Letter we present a search in apreviously unexplored region of LSTC phase space with M ( π T ) < ∼ M ( ρ T ) where ρ T decays predominantly to a W Z boson pair.We perform the search using data collected with theD0 detector [17] at the Fermilab Tevatron p ¯ p collider ata center of mass energy of √ s = 1 .
96 TeV. After apply-ing data quality and trigger requirements, the integratedluminosity corresponds to 4.1 fb − .The Monte Carlo (MC) samples for resonant W Z signal and SM backgrounds are generated using pythia [18], with the exception of Z + jets and t ¯ t pro-cesses that are generated using alpgen [19] interfacedwith pythia for showering and hadronization. All MCsamples are passed through a full geant [20] simulationof the D0 detector. The MC is corrected to describethe luminosity dependence of the trigger and reconstruc-tion efficiencies in data and the contribution from mul-tiple p ¯ p interactions. The MC sample for signal is pro-duced assuming SSM W ′ production for masses startingat 180, 190, 200 GeV and then up to 1 TeV in steps of50 GeV, using CTEQ6L1 [21] parton distribution func-tions (PDF). The interference between signal and theSM s -channel W Z production [22] is negligible and isnot taken into account. We generate technicolor
W Z samples using typical parametrization of the LSTC phe-nomenology implemented in pythia [23] to estimate theleading order cross section, efficiency, and acceptance ofthe selection criteria of the ρ T → W Z production. AllMC samples are normalized to the integrated luminos-ity using next-to-leading order cross section calculations,with the exception of the W ′ signal cross section, whichis known to next-to-next-to-leading order (NNLO) [24].All MC samples are subject to the same event selectionas applied to data.In this search we select events where both the W andthe Z bosons decay leptonically and consider only finalstates with electrons and muons. Candidate events withat least two final state electrons are selected using single-electron triggers, while those with at least two muons are selected using single-muon triggers resulting in effi-ciencies of 100% and 92% respectively for signal events.The events are required to have missing transverse energy E / T >
30 GeV [25] (from the undetected neutrino) andat least three charged leptons with transverse momenta p T >
20 GeV satisfying the electron or muon identifi-cation criteria described below. An electron candidateis identified as a central track matched to an isolatedcluster of energy in the calorimeter, with a shower shapeconsistent with that of an electron, in the pseudorapidityrange | η | < . . < | η | < .
5. A muon candidate isreconstructed from segments in the muon spectrometermatched to a central track, and is required to be within | η | <
2. The muon candidate must be isolated from otheractivity in the tracker and calorimeter.The selection of
W Z candidate events is done in twosteps. We first require the presence of a candidate Z bo-son by selecting the electron pairs and muon pairs withopposite electric charges that have invariant mass nearestto the mass of the Z boson. The reconstructed mass ofthe Z boson candidate must be between 80 and 102 GeVfor an electron pair and between 70 and 110 GeV for amuon pair. Then, we select the highest transverse mo-mentum lepton among the remaining lepton candidatesin the event as the lepton from the W boson decay. The W and Z bosons produced from heavy resonances canbe highly boosted, resulting in a large spatial separationbetween leptons from the W and Z decays. To reducebackground, we require the lepton from the W boson de-cay to be separated by ∆ R = p (∆ η ) + (∆ φ ) > . Z decay leptons.Several background processes contribute to the trilep-ton + E / T final state. The largest background having atleast three genuine leptons in the final state is from SM W Z production, followed by the ZZ process, where oneof the leptons from the Z boson is not reconstructed andgives rise to E / T . These are estimated from MC simula-tion. The instrumental background is due to misidentifi-cation of a lepton in processes such as Z + jets, Zγ , and t ¯ t . Contribution from t ¯ t is estimated from MC simulationand found to be negligible. Z + jets and Zγ productionsare the major instrumental backgrounds and they are es-timated using data driven techniques described below.Jets from Z + jets production can be misidentified aseither an electron or a muon from W boson decay. Toestimate this contribution, we select a sample of Z bo-son decays with an additional ”false” lepton candidatefor each final state. For the Z +electron final state thelepton candidate is required to have most of its energydeposited in the electromagnetic calorimeter and satisfythe electron isolation criteria, but at the same time ashower shape inconsistent with that of an electron. Forthe Z +muon final state, the lepton candidate is requiredto fail the isolation criteria used to select muons. Theserequirements ensure that the lepton is either a misidenti-fied jet or a lepton from a semileptonic decay of a heavy-flavor quark. The contribution from the Z + jets back-ground with misidentified leptons is estimated by scalingthe number of events in this sample with a p T -dependentratio of misidentified leptons passing the two differentsets of criteria measured in a multijet data sample de-pleted of true isolated leptons.The channels with W → eν decays can be mimickedby the initial or final state radiation Zγ processes wherea photon is either incorrectly matched to a track, or con-verts, and one of the conversion electrons is selected asthe candidate for W boson decay. To estimate the con-tribution from this background, we measure the rate atwhich a photon can be misidentified as an electron in Z → µµγ final states in data, as it offers a virtuallybackground-free source of photons because of the µµγ invariant mass constraint to the M ( Z ). We choose themuon decay of the Z boson to avoid ambiguity in assign-ing the electromagnetic showers in the eeγ final states.The Zγ contribution is estimated by folding in the p T -dependent photon to electron misidentification rate withthe p T distribution of γ in the Zγ Monte Carlo simula-tion [26].The selection criteria yield 9 events in data with anestimate of 10.2 ± Zγ background estimation a systematic uncertaintyof 100% for any potential mis-modeling of E / T . The dom-inant systematic uncertainty on Z + jets background isfrom the limited statistics of the Z + ” false ” lepton sam-ple. We estimate this uncertainty to be 40%. Finally, theuncertainty on integrated luminosity is 6.1% [27], and theuncertainty on the theoretical NNLO production crosssection of signal is 5%. Source Total W ′ (500 GeV) 4 . ± . W Z . ± . ZZ . ± . Z + jets 0 . ± . Zγ . ± . . ± . W ′ mass of 500 GeV and expected numberof background events with statistical and systematic uncer-tainties. As the number of observed candidates is consistentwith the background-only hypothesis, we set limits on W ′ production in a modified frequentist approach [28]that uses a log-likelihood ratio ( LLR ) test statistic [29].It calculates the confidence levels for the signal + back-ground, CL s + b , and background-only hypothesis, CL b ,by integrating the LLR distributions obtained from sim-ulated pseudo-experiments using Poisson statistics. Sys-tematic uncertainties are treated as uncertainties on theexpected number of signal and background events. Thisensures that the uncertainties and their correlations arepropagated to the outcome with proper weights. The95% confidence level (C.L.) limit on the cross sectionis then defined as a cross section for which the ratio CL s = CL s + b /CL b is 0.05.We use the W Z transverse mass to discriminate be-tween the W ′ signal and the backgrounds in the limitsetting procedure. It is calculated as M T = q ( E ZT + E WT ) − ( p Zx + p Wx ) − ( p Zy + p Wy ) , where E ZT and E WT are the scalar sums of the trans-verse momenta of the decay products of the Z and W candidates, respectively; while p Zx , p Wx , p Zy , and p Wy areobtained by summing the x and y components of mo-menta of the respective decay particles. In these sums,the transverse momentum of the neutrino arising fromthe W boson decay is inferred from the direction andmagnitude of E / T . The distribution of the W Z trans-verse mass is given in Fig. 1 for data, backgrounds, andtwo signal hypotheses. We obtain a limit on the pro-duction cross section of W ′ multiplied by the branch-ing ratio B ( W ′ → W Z ) as a function of the M ( W ′ ) asshown in Fig. 2. This is the first limit to date on resonant W ′ → W Z production. Assuming SSM production, weexclude a W ′ with mass 188 < M ( W ′ ) <
520 GeV at95% C.L.. This result agrees with the expected sensitiv-ity limit of 188 < M ( W ′ ) <
497 GeV.We also study the sensitivity to other models that pre-dict a W ′ -like resonance with width greater than in theSSM by varying the width of the W ′ resonance whilekeeping σ ( W ′ ) × B ( W ′ → W Z ) fixed to the SSM value.We find that the limits slightly degrade but stay within1 standard deviation (s.d.) around the expected sensi-tivity limits for models with widths up to 25% of theresonance mass. Since the limits have a limited sensitiv-ity to the width of the W ′ , we can exclude more generalmodels that predict W ′ bosons with arbitrary couplingsto the W and Z bosons. We interpret the results in termsof the W ′ W Z trilinear coupling normalized to the SSMvalue as function of the W ′ mass (see Fig. 3).The limits on the resonant W Z production cross sec-tion σ × B ( W ′ → W Z ) yield stringent constraints onthe LSTC and exclude most of the allowed phase spacewhere ρ T → W Z decay is dominant. The excluded and
Mode
W Z ZZ Z + jets Zγ Total W ′ Dataeee 1 . ± . . ± .
02 0 . ± .
01 0 . ± .
03 1 . ± .
33 1 . ± .
28 3ee µ . ± . . ± .
06 0 . ± . < .
01 2 . ± .
49 1 . ± .
31 2e µµ . ± . . ± .
03 0 . ± .
02 0 . ± .
07 2 . ± .
46 0 . ± .
22 2 µµµ . ± . . ± .
12 0 . ± . < .
01 4 . ± .
89 1 . ± .
34 2TABLE II: Background estimation from the leading sources, the total background, expected signal, and observed events foreach signature. The signal corresponds to a SSM W ′ with a mass of 500 GeV. The uncertainties reflect both the statistics ofthe MC and data samples and systematics. WZ transverse mass (GeV)
100 200 300 400 500 600 700 E v e n t s / G e V DataWZ Monte Carlo, jet, Z) γ Z+X (X=W’ 400 GeV SSM signalW’ 500 GeV SSM signal -1 , 4.1 fb ∅ D WZ transverse mass (GeV)
100 200 300 400 500 600 700 E v e n t s / G e V WZ transverse mass (GeV)
100 200 300 400 500 600 700 E v e n t s / G e V FIG. 1: Transverse mass distribution of the
W Z system indata with the major SM backgrounds and two SSM W ′ masshypotheses overlaid (color online). expected limits at 95% C.L., as a function of the ρ T and π T masses, are shown in Fig. 4.In summary, we have presented a search for hypothet-ical W ′ particles decaying to a pair of W Z bosons usingleptonic W and Z decay modes in 4.1 fb − of TevatronRun II data. We observe no evidence of resonant W Z production, and set limits on the production cross sec-tion σ × B ( W ′ → W Z ). Within the SSM we exclude W ′ masses between 188 and 520 GeV at 95% C.L. This isthe best limit to date on W ′ → W Z production and iscomplementary to previous searches [13–15] for W ′ de-cay to fermions. These limits are less stringent for themodels that predict W ′ with width greater than thatpredicted by the SSM model, but stay within the 1 s.d.band around the expected SSM limits for widths below25% of the W ′ mass. The original limits are also in-terpreted within the technicolor model. We exclude ρ T with mass between 208 and 408 GeV at 95% C.L. for M ( ρ T ) < M ( π T ) + M ( W ). These are the most stringentconstraints on a typical LSTC phenomenology model [23]when ρ T decays predominantly to W Z boson pair.We thank Kenneth Lane for useful discussions andhelp with interpretation of the results within the TCSMparameter space and we thank the staffs at Fermilaband collaborating institutions, and acknowledge supportfrom the DOE and NSF (USA); CEA and CNRS/IN2P3 (GeV) W’ M
200 300 400 500 600 700 800 900 1000 W Z ) ( pb ) → x BR ( W ’ σ -1
10 Expected 95% C.L. limitObserved 95% C.L. limit WZ), SSM → x B(W’ σ ± (GeV) W’ M
200 300 400 500 600 700 800 900 1000 W Z ) ( pb ) → x BR ( W ’ σ -1 -1 , 4.1 fb ∅ D FIG. 2: Observed and expected 95% C.L. upper limits and ± B ( W ′ → W Z ) with the SSM prediction overlaid(color online).
W’ mass (GeV)
200 300 400 500 600 700 800 900 1000 W ’ W Z c oup li ng s t r e ng t h / SS M Excluded 95% C.L. regionExpected 95% C.L. limitSSM value
W’ mass (GeV)
200 300 400 500 600 700 800 900 1000 W ’ W Z c oup li ng s t r e ng t h / SS M -1 , 4.1 fb ∅ D FIG. 3: Expected and excluded area of the W ′ W Z couplingstrength normalized to the SSM value as a function of the W ′ mass (color online). (France); FASI, Rosatom and RFBR (Russia); CNPq,FAPERJ, FAPESP and FUNDUNESP (Brazil); DAEand DST (India); Colciencias (Colombia); CONACyT(Mexico); KRF and KOSEF (Korea); CONICET andUBACyT (Argentina); FOM (The Netherlands); STFCand the Royal Society (United Kingdom); MSMT and ) (GeV) T ρ M(
200 250 300 350 400 ) ( G e V ) T π M ( T π T π → T ρ T π W → T ρ Excluded 95% C.L. regionExpected 95% C.L. limit threshold T π T π→ T ρ threshold T π W → T ρ -1 , 4.1 fb ∅ D FIG. 4: Expected and excluded areas of the π T vs. ρ T massesare given with the thresholds of the ρ T → W π T and ρ T → π T π T overlaid (color online). GACR (Czech Republic); CRC Program, CFI, NSERCand WestGrid Project (Canada); BMBF and DFG (Ger-many); SFI (Ireland); The Swedish Research Council(Sweden); CAS and CNSF (China); and the Alexandervon Humboldt Foundation (Germany). [a] Visitor from Augustana College, Sioux Falls, SD, USA.[b] Visitor from Rutgers University, Piscataway, NJ, USA.[c] Visitor from The University of Liverpool, Liverpool, UK.[d] Visitor from SLAC, Menlo Park, CA, USA.[e] Visitor from Centro de Investigacion en Computacion -IPN, Mexico City, Mexico.[f] Visitor from ECFM, Universidad Autonoma de Sinaloa,Culiac´an, Mexico.[g] Visitor from Universit¨at Bern, Bern, Switzerland.[h] Visitor from Universit¨at Z¨urich, Z¨urich, Switzerland.[9] J.C. Pati, A. Salam, Phys. Rev. D , 275 (1974) [Erratum-ibid. D , 703 (1975)]; G. Altarelli, B. Mele,M. Ruiz-Altaba, Z. Phys. C , 109 (1989) [Erratum-ibidC , 676 (1990)]; P. Langacker, Rev. Mod. Phys. ,1199 (2009), and references therein.[10] H. He et al. , Phys. Rev. D , 031701 (2008); A. Belyaev,arXiv:0711.1919 [hep-ph]; K. Agashe et al. , Phys. Rev. D , 075007, 2009.[11] M. Perelstein, Prog. Part. Nucl. Phys. , 247 (2007).[12] E. Eichten and K. Lane, Phys. Lett. B , 235 (2008);K. Lane, Phys. Rev. D , 075007 (1999).[13] D. Acosta et al. , Phys. Rev. Lett. , 081802 (2003).[14] A. Abulencia et al. , Phys. Rev. D , 091101 (2007).[15] V. M. Abazov et al. , Phys. Rev. Lett. , 211803 (2008).[16] V. M. Abazov et al. , Phys. Rev. Lett. , 221801 (2007).[17] V.M. Abazov et al. , Nucl. Instrum. Methods Phys. Res.A , 463 (2006).[18] T. Sj¨ostrand, S. Mrenna, and P. Skands, J. High En-ergy Phys. , 026 (2006); we used 6.419.[19] M. L. Mangano et al. , J. High Energy Phys. , 1 (2003).[20] GEANT
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