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Search for $widetilde{W}_1widetilde{Z}_2$ Production via Trilepton Final States in $pbar{p}

FERMILAB Pub-95/385-E

Search for W 1 Z 2 Production via Trilepton Final √ States in pp Collisions at s = 1.8 TeV
S. Abachi,14 B. Abbott,28 M. Abolins,25 B.S. Acharya,44 I. Adam,12 D.L. Adams,37

arXiv:hep-ex/9512004v2 7 Dec 1995

? M. Adams,17 S. Ahn,14 H. Aihara,22 J. Alitti,40 G. Alvarez,18 G.A. Alves,10 E. Amidi,29 N. Amos,24 E.W. Anderson,19 S.H. Aronson,4 R. Astur,42 R.E. Avery,31 A. Baden,23 V. Balamurali,32 J. Balderston,16 B. Baldin,14 J. Bantly,5 J.F. Bartlett,14 K. Bazizi,39 J. Bendich,22 S.B. Beri,34 I. Bertram,37 V.A. Bezzubov,35 P.C. Bhat,14 V. Bhatnagar,34 M. Bhattacharjee,13 A. Bischo?,9 N. Biswas,32 G. Blazey,14 S. Blessing,15 P. Bloom,7 A. Boehnlein,14 N.I. Bojko,35 F. Borcherding,14 J. Borders,39 C. Boswell,9 A. Brandt,14 R. Brock,25 A. Bross,14 D. Buchholz,31 V.S. Burtovoi,35 J.M. Butler,3 W. Carvalho,10 D. Casey,39 H. Castilla-Valdez,11 D. Chakraborty,42 S.-M. Chang,29 S.V. Chekulaev,35 L.-P. Chen,22 W. Chen,42 S. Chopra,34 B.C. Choudhary,9 J.H. Christenson,14 M. Chung,17 D. Claes,42 A.R. Clark,22 W.G. Cobau,23 J. Cochran,9 W.E. Cooper,14 C. Cretsinger,39 D. Cullen-Vidal,5 M.A.C. Cummings,16 D. Cutts,5 O.I. Dahl,22 K. De,45 M. Demarteau,14 R. Demina,29 K. Denisenko,14 N. Denisenko,14 D. Denisov,14 S.P. Denisov,35 H.T. Diehl,14 M. Diesburg,14 G. Di Loreto,25 R. Dixon,14 P. Draper,45 J. Drinkard,8 Y. Ducros,40 S.R. Dugad,44 S. Durston-Johnson,39 D. Edmunds,25 J. Ellison,9 V.D. Elvira,6 R. Engelmann,42 S. Eno,23 G. Eppley,37 P. Ermolov,26 O.V. Eroshin,35 V.N. Evdokimov,35 S. Fahey,25 T. Fahland,5 M. Fatyga,4 M.K. Fatyga,39 J. Featherly,4 S. Feher,42 D. Fein,2 T. Ferbel,39 G. Finocchiaro,42 H.E. Fisk,14 Y. Fisyak,7 E. Flattum,25 G.E. Forden,2 M. Fortner,30 K.C. Frame,25 P. Franzini,12 S. Fuess,14 E. Gallas,45 A.N. Galyaev,35 T.L. Geld,25 R.J. Genik II,25 K. Genser,14 C.E. Gerber,6 B. Gibbard,4 V. Glebov,39 S. Glenn,7 J.F. Glicenstein,40 B. Gobbi,31 M. Goforth,15 A. Goldschmidt,22 B. G?mez,1 o P.I. Goncharov,35 J.L. Gonz?lez Sol? 11 H. Gordon,4 L.T. Goss,46 N. Graf,4 a ?s, P.D. Grannis,42 D.R. Green,14 J. Green,30 H. Greenlee,14 G. Gri?n,8 N. Grossman,14 1

P. Grudberg,22 S. Gr¨ nendahl,39 W.X. Gu,14,? G. Guglielmo,33 J.A. Guida,2 J.M. Guida,4 u W. Guryn,4 S.N. Gurzhiev,35 P. Gutierrez,33 Y.E. Gutnikov,35 N.J. Hadley,23 H. Haggerty,14 S. Hagopian,15 V. Hagopian,15 K.S. Hahn,39 R.E. Hall,8 S. Hansen,14 R. Hatcher,25 J.M. Hauptman,19 D. Hedin,30 A.P. Heinson,9 U. Heintz,14 R. Hern?ndez-Montoya,11 T. Heuring,15 R. Hirosky,15 J.D. Hobbs,14 B. Hoeneisen,1,? a J.S. Hoftun,5 F. Hsieh,24 Tao Hu,14,? Ting Hu,42 Tong Hu,18 T. Huehn,9 S. Igarashi,14 A.S. Ito,14 E. James,2 J. Jaques,32 S.A. Jerger,25 J.Z.-Y. Jiang,42 T. Jo?e-Minor,31 H. Johari,29 K. Johns,2 M. Johnson,14 H. Johnstad,43 A. Jonckheere,14 M. Jones,16 H. J¨stlein,14 S.Y. Jun,31 C.K. Jung,42 S. Kahn,4 G. Kalb?eisch,33 J.S. Kang,20 o R. Kehoe,32 M.L. Kelly,32 A. Kernan,9 L. Kerth,22 C.L. Kim,20 S.K. Kim,41 A. Klatchko,15 B. Klima,14 B.I. Klochkov,35 C. Klopfenstein,7 V.I. Klyukhin,35 V.I. Kochetkov,35 J.M. Kohli,34 D. Koltick,36 A.V. Kostritskiy,35 J. Kotcher,4 J. Kourlas,28 A.V. Kozelov,35 E.A. Kozlovski,35 M.R. Krishnaswamy,44 S. Krzywdzinski,14 S. Kunori,23 S. Lami,42 G. Landsberg,14 J-F. Lebrat,40 A. Le?at,26 H. Li,42 J. Li,45 Y.K. Li,31 Q.Z. Li-Demarteau,14 J.G.R. Lima,38 D. Lincoln,24 S.L. Linn,15 J. Linnemann,25 R. Lipton,14 Y.C. Liu,31 F. Lobkowicz,39 S.C. Loken,22 S. L¨k¨s,42 L. Lueking,14 A.L. Lyon,23 A.K.A. Maciel,10 o o R.J. Madaras,22 R. Madden,15 S. Mani,7 H.S. Mao,14,? S. Margulies,17 R. Markelo?,30 L. Markosky,2 T. Marshall,18 M.I. Martin,14 M. Marx,42 B. May,31 A.A. Mayorov,35 R. McCarthy,42 T. McKibben,17 J. McKinley,25 T. McMahon,33 H.L. Melanson,14 J.R.T. de Mello Neto,38 K.W. Merritt,14 H. Miettinen,37 A. Mincer,28 J.M. de Miranda,10 C.S. Mishra,14 M. Mohammadi-Baarmand,42 N. Mokhov,14 N.K. Mondal,44 H.E. Montgomery,14 P. Mooney,1 H. da Motta,10 M. Mudan,28 C. Murphy,18 C.T. Murphy,14 F. Nang,5 M. Narain,14 V.S. Narasimham,44 A. Narayanan,2 H.A. Neal,24 J.P. Negret,1 E. Neis,24 P. Nemethy,28 D. Neˇi?,5 M. Nicola,10 D. Norman,46 L. Oesch,24 sc V. Oguri,38 E. Oltman,22 N. Oshima,14 D. Owen,25 P. Padley,37 M. Pang,19 A. Para,14 C.H. Park,14 Y.M. Park,21 R. Partridge,5 N. Parua,44 M. Paterno,39 J. Perkins,45 A. Peryshkin,14 M. Peters,16 H. Piekarz,15 Y. Pischalnikov,36 V.M. Podstavkov,35 B.G. Pope,25 H.B. Prosper,15 S. Protopopescu,4 D. Puˇelji?,22 J. Qian,24 P.Z. Quintas,14 s c 2

R. Raja,14 S. Rajagopalan,42 O. Ramirez,17 M.V.S. Rao,44 P.A. Rapidis,14 L. Rasmussen,42 A.L. Read,14 S. Reucroft,29 M. Rijssenbeek,42 T. Rockwell,25 N.A. Roe,22 P. Rubinov,31 R. Ruchti,32 S. Rusin,26 J. Rutherfoord,2 A. Santoro,10 L. Sawyer,45 R.D. Schamberger,42 H. Schellman,31 J. Sculli,28 E. Shabalina,26 C. Sha?er,15 H.C. Shankar,44 Y.Y. Shao,14,? R.K. Shivpuri,13 M. Shupe,2 J.B. Singh,34 V. Sirotenko,30 W. Smart,14 A. Smith,2 R.P. Smith,14 R. Snihur,31 G.R. Snow,27 S. Snyder,4 J. Solomon,17 P.M. Sood,34 M. Sosebee,45 M. Souza,10 A.L. Spadafora,22 R.W. Stephens,45 M.L. Stevenson,22 D. Stewart,24 D.A. Stoianova,35 D. Stoker,8 K. Streets,28 M. Strovink,22 A. Sznajder,10 A. Taketani,14 P. Tamburello,23 J. Tarazi,8 M. Tartaglia,14 T.L. Taylor,31 J. Thompson,23 T.G. Trippe,22 P.M. Tuts,12 N. Varelas,25 E.W. Varnes,22 P.R.G. Virador,22 D. Vititoe,2 A.A. Volkov,35 A.P. Vorobiev,35 H.D. Wahl,15 G. Wang,15 J. Warchol,32 M. Wayne,32 H. Weerts,25 F. Wen,15 A. White,45 J.T. White,46 J.A. Wightman,19 J. Wilcox,29 S. Willis,30 S.J. Wimpenny,9 J.V.D. Wirjawan,46 J. Womersley,14 E. Won,39 D.R. Wood,14 H. Xu,5 R. Yamada,14 P. Yamin,4 C. Yanagisawa,42 J. Yang,28 T. Yasuda,29 C. Yoshikawa,16 S. Youssef,15 J. Yu,39 Y. Yu,41 D.H. Zhang,14,? Q. Zhu,28 Z.H. Zhu,39 D. Zieminska,18 A. Zieminski,18 and A. Zylberstejn40 (D? Collaboration)
1 Universidad 2 University 3 Boston 4 Brookhaven 5 Brown

de los Andes, Bogot?, Colombia a

of Arizona, Tucson, Arizona 85721

University, Boston, Massachusetts 02215 National Laboratory, Upton, New York 11973

University, Providence, Rhode Island 02912 de Buenos Aires, Buenos Aires, Argentina of California, Davis, California 95616 of California, Irvine, California 92717

6 Universidad

7 University 8 University 9 University

of California, Riverside, California 92521

3

10 LAFEX,

Centro Brasileiro de Pesquisas F?sicas, Rio de Janeiro, Brazil ?
11 CINVESTAV, 12 Columbia

Mexico City, Mexico

University, New York, New York 10027 University, Delhi, India 110007

13 Delhi 14 Fermi

National Accelerator Laboratory, Batavia, Illinois 60510 State University, Tallahassee, Florida 32306 of Hawaii, Honolulu, Hawaii 96822

15 Florida

16 University 17 University

of Illinois at Chicago, Chicago, Illinois 60607 University, Bloomington, Indiana 47405 State University, Ames, Iowa 50011 University, Seoul, Korea University, Pusan, Korea

18 Indiana 19 Iowa

20 Korea

21 Kyungsung 22 Lawrence

Berkeley National Laboratory and University of California, Berkeley, California 94720
23 University

of Maryland, College Park, Maryland 20742 of Michigan, Ann Arbor, Michigan 48109

24 University 25 Michigan

State University, East Lansing, Michigan 48824 State University, Moscow, Russia

26 Moscow 27 University 28 New

of Nebraska, Lincoln, Nebraska 68588

York University, New York, New York 10003 University, Boston, Massachusetts 02115

29 Northeastern 30 Northern

Illinois University, DeKalb, Illinois 60115 University, Evanston, Illinois 60208

31 Northwestern 32 University

of Notre Dame, Notre Dame, Indiana 46556 of Oklahoma, Norman, Oklahoma 73019 of Panjab, Chandigarh 16-00-14, India

33 University 34 University 35 Institute

for High Energy Physics, 142-284 Protvino, Russia University, West Lafayette, Indiana 47907 University, Houston, Texas 77251

36 Purdue

37 Rice

4

38 Universidade 39 University 40 CEA,

Estadual do Rio de Janeiro, Brazil

of Rochester, Rochester, New York 14627

DAPNIA/Service de Physique des Particules, CE-SACLAY, France
41 Seoul

National University, Seoul, Korea

42 State

University of New York, Stony Brook, New York 11794
43 SSC

Laboratory, Dallas, Texas 75237

44 Tata

Institute of Fundamental Research, Colaba, Bombay 400005, India
45 University 46 Texas

of Texas, Arlington, Texas 76019

A&M University, College Station, Texas 77843 (February 7, 2008)

Abstract
We have searched for associated production of the lightest chargino, W1 , and next-to-lightest neutralino, Z2 , of the Minimal Supersymmetric Stan√ dard Model in p? collisions at s = 1.8 TeV using the D? detector at p the Fermilab Tevatron collider. Data corresponding to an integrated lu-

minosity of 12.5±0.7 pb?1 were examined for events containing three isolated leptons. No evidence for W1 Z2 pair production was found. Limits on σ(W1 Z2 )Br(W1 → lν Z1 )Br(Z2 → l?Z1 ) are presented. l

Submitted to the Physical Review Letters

Typeset using REVTEX 5

Supersymmetry (SUSY) is a symmetry which relates bosons and fermions [1]. Supersymmetric extensions of the Standard Model (SM) are attractive because they remove the “?ne tuning” problem associated with loop corrections to the mass of the Higgs boson and provide a basis for gauge coupling uni?cation at a high mass scale. One consequence of these models is the introduction of a SUSY partner (sparticle) for each SM state. Every sparticle and SM particle is assigned an internal quantum number called R-parity. If Rparity is conserved (as assumed in this analysis), then sparticle states are produced in pairs and there must be one sparticle which does not decay. This sparticle is referred to as the Lightest Supersymmetric Particle (LSP). The SUSY framework which introduces the fewest additional particles is known as the Minimal Supersymmetric Standard Model (MSSM) [2]. If the requirement is made that SUSY be a locally invariant gauge symmetry, the result is a theoretical framework known as supergravity (SUGRA) [3]. In the MSSM and minimal SUGRA there are two chargino states (Wi,i=1,2 ) and four neutralino states (Zi,i=1,4), corresponding to mixtures of the SUSY partners of the Higgs bosons, W and Z bosons, and the photon. (In some of the literature an alternate notation
? is used: χ± i,i=1,2 for charginos and χi,i=1,4 for neutralinos.) In most regions of the SUGRA

parameter space not excluded by previous experiments, the LSP is the lightest neutralino [4] and thus escapes detection. The best limits to date on the masses of the W 1 and Z 2 states come from the LEP experiments [5]; the current limits are MW1 > 45 GeV/c2 and MZ2 > 40 ? 45 GeV/c2 . At pp colliders charginos and neutralinos can be produced in pairs, with W 1 Z 2 pairs having the largest cross section over much of the parameter space [6]. Production cross sections O(100–10) pb are possible at the Tevatron for W 1 masses between 45 and 100 GeV/c2 [7,8]. The W 1 can decay into q q ′ or l? plus an LSP, while the Z 2 can decay into ? ν q q or l? plus an LSP. The presence of neutrinos or LSP’s among the decay products will ? l / generally lead to missing transverse energy (ET ). The ?nal state consisting of three leptons / and ET (and little hadronic activity) has few SM backgrounds and is the subject of the present analysis. 6

The spectra of the transverse momenta (pT ) of the ?nal state leptons can be relatively soft due to the three-body decays of the W 1 and Z 2 involving massive non-interacting particles. Figure 1 shows the expected pT spectra of the ?nal state leptons as well as / the ET distribution at the physics generator level for simulated W1 Z2 → 3l events, with MW1 = 56 GeV/c2 . These Monte Carlo events follow the mass relation common to many SUSY models: MW1 ≈ MZ2 ≈ 2MZ1 . The data used in this analysis were obtained using the D? detector at the Fermilab Tevatron pp collider operating at a center of mass energy of 1.8 TeV. The total integrated luminosity used in this analysis from the 1992–1993 Tevatron run was 12.5 ± 0.7 pb?1 . The D? detector has three major subsystems: central tracking detectors (with no central magnetic ?eld), uranium–liquid argon electromagnetic and hadronic calorimeters, and a muon spectrometer. The detector and data acquisition system are described in detail elsewhere [9]. The central tracking system is used to identify charged tracks in the pseudorapidity range |η| ≤ 3.5. The calorimeters provide full angular coverage for |η| ≤ 4.0, with transverse segmentation ?η × ?φ = 0.1 × 0.1, where φ is the azimuthal angle. The muon system consists of proportional drift chambers and magnetized iron toroids with coverage extending to |η| ≤ 3.3. Electrons were identi?ed as calorimeter clusters having at least 90% of their energy deposition in the electromagnetic calorimeter, with one or more tracks pointing to the cluster. Jets were reconstructed from energy deposition in the calorimeters using a cone algorithm √ with cone size R = ?η 2 + ?φ2 = 0.5. Muon tracks were reconstructed using hits in the muon drift chambers; their momenta were calculated from the bend of the tracks in the toroids. Combinations of single lepton and dilepton triggers were used for the four ?nal states (eee, ee?, e??, and ???). These triggers included: a single muon with p? > 15 GeV/c; two T muons with p? > 3 GeV/c; one muon with p? > 5 GeV/c plus one electromagnetic cluster T T
e e with ET > 7 GeV; one electromagnetic cluster with ET > 20 GeV; and two electromagnetic e clusters with ET > 10 GeV. The integrated luminosity per channel is given in Table I.

7

Events passing the trigger requirements were selected o?ine by requiring three or more
e reconstructed leptons (electrons or muons) having ET > 5 GeV or p? > 5 GeV/c, with T

|ηe | < 2.5 or |η? | < 1.7. There were 2827 events in this initial data sample. Electrons and muons in these events were then required to pass the quality cuts described below. Electrons were required to have transverse and longitudinal shower pro?les consistent with expectations based on detailed Monte Carlo studies [10], to have no more than two tracks pointing to the calorimeter cluster, and to have an electromagnetic isolation I < 0.15, where I = [Etot ? EEM ]/EEM , Etot is the total cluster energy inside a cone of radius R = 0.4, and EEM is the electromagnetic energy inside a cone of R = 0.2. For electrons with ET between 5 and 10 GeV, the isolation cut was relaxed to I< 0.2 to increase e?ciency. Muons were required to have a separation from any jet of at least R = 0.5, to be aligned with minimum ionizing energy deposition in at least 50% of all calorimeter layers and in at least 60% of the hadronic calorimeter layers, and to have either a matching track in the central detectors or impact parameters in the rz (bend) and xy (non-bend) views consistent with the muon having been produced at the primary event vertex [10]. To reduce cosmic ray background, muons were required to be in time with the beam crossing and any muon pair having both polar and azimuthal opening angles greater than 165? was rejected. There were 19 events after these quality cuts. The following topological cuts were applied / / to these events. For the eee channel, events were required to have ET > 10 GeV, with the ET reconstructed using only energy deposited in the calorimeters. This cut reduced background from Z/γ → e+ e? events with a third electron from either a photon conversion (including π 0 → γγ) into an unresolved e+ e? pair or a jet which was reconstructed as an electron. Since extra material in the forward region enhances the photon conversion probability, the data exhibit an excess of electrons in the forward region while the signal distributions peak in the central region. Therefore, a cut was applied in the eee and ee? channels to exclude events with more than one electron in the region |η| > 1.7. For the e?? and ??? channels, muon pairs were required to have an invariant mass greater than 5 GeV/c2 , which reduced background from J/ψ events and the combinatoric background in the reconstruction of 8

muons. Table I summarizes the e?ect of the cuts on each of the channels. We see no candidate events consistent with W 1 Z 2 pair production and subsequent decay into trilepton ?nal states. Detection e?ciencies were determined using a combination of data and Monte Carlo simulations. Monte Carlo signal events were generated using ISAJET [11] and processed with a full simulation of the D? detector based on the GEANT [12] program. Seven sets of events were generated, with the mass of the W 1 varying from 45 to 100 GeV/c2 . Because of the correlation between the masses of the W 1 , Z 2 , and Z 1 , e?ciencies can be parametrized as a function of MW1. These Monte Carlo events were used to determine kinematic and geometric acceptances only. Electron identi?cation e?ciencies were determined from a set of simulated single electron events generated in six ET bins between 5 and 25 GeV. These were overlaid with minimum bias events from collider data in order to include the e?ects of the underlying event and any noise in the calorimeter on electron isolation and shower pro?le. The results of these studies for high ET electrons were veri?ed by analyzing a sample of Z → ee events [13] in which one electron was required to pass all cuts and the second electron was then used as an unbiased estimator for each cut. Similarly, muon identi?cation e?ciencies were based on Z → ?? and J/ψ → ?? event samples. These two sets provided independent estimates of e?ciencies for both high and low pT muons. Electron and muon identi?cation e?ciencies were parametrized as a function of the electron ET or muon pT and incorporated with the topological cuts described above to determine the overall analysis e?ciency for each set of Monte Carlo signal events. These e?ciencies are shown in Fig. 2 for each ?nal state, along with a parametrized ?t [13], as a function of the W 1 mass. Backgrounds were estimated from data whenever possible, supplemented with Monte Carlo simulations. Standard Model processes which produce three or more isolated leptons, such as vector boson pair production and semileptonic decays in heavy ?avor production, 9

are expected to yield less than 0.1 event in any channel. Thus the primary sources of background are single lepton and dilepton events with one or more spurious leptons. The sources of spurious electrons are jet ?uctuations and unresolved e+ e? pairs from photon conversions. The probability of a jet faking an isolated muon is negligible. The background from fake electrons was calculated from data using dilepton events with one or more additional photons and/or jets. The expected number of events was determined by multiplying the number of events seen in data by the probability of a photon conversion or the rate for a jet to fake an electron [13]. The primary source of background in the ??? channel is heavy ?avor (b? and c?) events with the muons produced at large angle to the b c jets. The total background for each ?nal state is included in Table I. Based on zero candidate events, we present a 95% con?dence level upper limit on the cross section for producing W 1 Z 2 pairs times the branching ratio into any one of the trilepton ?nal states. The results from the four channels were combined in the calculation of the limit, with the assumption that Br(eee) = Br(ee?) = Br(e??) = Br(???). Uncertainties in this calculation include the uncertainty in the luminosity (5.4%) and uncertainties in the overall analysis detection e?ciencies (between 15% and 25% of the value) due to Monte Carlo statistics, systematic errors in the determination of lepton identi?cation e?ciencies, systematic errors in the trigger e?ciencies, and systematic errors arising from energy scale corrections. To construct this limit we used the Bayesian approach of [14], with the distribution of systematic errors represented by a Gaussian and a ?at prior probability distribution for the signal cross section. In Fig. 3 we show the resulting limit in the region above the LEP limit [5]. For comparison, we show three bands of theoretical curves. Band (a) shows the ISAJET production cross section obtained with a wide range of input parameters, multiplied by a branching ratio of
1 . 9

The value of

1 9

for a single trilepton channel is obtained when the W1 and Z2 decay purely

leptonically and lepton universality is applied. Branching ratios of this order are predicted in models with very light sleptons, as for example the model of Ref. [8]. Bands (b) and (c) show the σ×Br values from ISAJET obtained with the following SUGRA input parameters: 10

m0 = [200, 900] GeV/c2 , m 1 = [50, 120] GeV/c2 , A0 = 0 and the sign of ? negative. Band
2

(b) is for tan β = 2 and band (c) for tan β = 4. In conclusion, we have searched for the associated production of chargino and neutralino pairs by looking for the reaction pp → W1 Z2 → 3l + X. We see no evidence for W 1 Z 2 production in 12.5 pb?1 of data. This leads to upper limits on σ(W1 Z2 )Br(W1 → lν Z1 )Br(Z2 → l?Z1 ) ranging from 3.1 pb for MW1 = 45 GeV/c2 to 0.6 pb for MW1 = 100 GeV/c2 . l We thank the Fermilab Accelerator, Computing, and Research Divisions, and the support sta?s at the collaborating institutions for their contributions to the success of this work. We also acknowledge the support of the U.S. Department of Energy, the U.S. National Science Foundation, the Commissariat ` L’Energie Atomique in France, the Ministry for a Atomic Energy and the Ministry of Science and Technology Policy in Russia, CNPq in Brazil, the Departments of Atomic Energy and Science and Education in India, Colciencias in Colombia, CONACyT in Mexico, the Ministry of Education, Research Foundation and KOSEF in Korea, CONICET and UBACYT in Argentina, and the A.P. Sloan Foundation.

11

REFERENCES
?

Visitor from IHEP, Beijing, China. Visitor from Univ. San Francisco de Quito, Ecuador. [1] Yu.A. Golfand and E.P. Likhtman, JETP Lett. 13, 323 (1971); D.V. Volkov and V.P. Akulov, Phys. Lett. B46, 109 (1973); J. Wess and B. Zumino, Nucl. Phys. B70, 39 (1974). [2] For a review of the MSSM see, e.g., H.E. Haber and G.L. Kane, Phys. Rep. 117, 75 (1985). [3] R. Arnowitt and P. Nath, Phys. Rev. Lett. 69, 725 (1992); P. Nath and R. Arnowitt, Phys. Lett. B287, 89 (1992) and B289, 368 (1992). [4] See e.g. H. Baer, M. Drees and X. Tata, Phys. Rev. D41, 3414 (1990). [5] T. Medcalf, “The Search for Supersymmetry with the Aleph Detector at LEP”; P. Lutz, “SUSY with DELPHI”; R. Brown, “Searches for New Particles in OPAL”; all in International Workshop on Supersymmetry and Uni?cation of Fundamental Interactions, P. Nath ed., World Scienti?c, Singapore (1993). [6] H. Baer, C.H. Chen, C. Kao and X. Tata, Phys. Rev. D52, 1565 (1995). [7] P. Nath and R. Arnowitt, Mod. Phys. Lett. A2, 331 (1987); R. Barbieri et al., Nucl. Phys B367, 28 (1993); H. Baer and X. Tata, Phys. Rev D47, 2739 (1993). [8] J. Lopez, D. V. Nanopoulos, Xu Wang, and A. Zichichi, Phys. Rev D48, 2062 (1993). [9] D? Collaboration, S. Abachi et al., Nucl. Instrum. Methods Phys. Res., Sect. A 338, 185 (1994), and references therein.

?

[10] S. Abachi et al., Phys. Rev. D52, 4877 (1995). [11] F. Paige and S. Protopopescu, in Supercollider Physics, p. 41, ed. D. Soper (World 12

Scienti?c, 1986); H. Baer, F. Paige, S. Protopopescu and X. Tata, in Proceedings of the Workshop on Physics at Current Accelerators and Supercolliders, ed. J. Hewett, A. White and D. Zeppenfeld, (Argonne National Laboratory, 1993). We used ISAJET version 7.06. [12] R. Brun and F. Carminati, “GEANT Detector Description and Simulation Tool,” CERN Program Library Long Writeup W5013 (1993) (unpublished). We used GEANT version 3.15. [13] M. Sosebee, University of Texas at Arlington, Ph.D. thesis, (1995) (unpublished). [14] Particle Data Group, Phys. Rev. D50, 1173 (1994).

13

Channel

eee

ee?

e??

???

Ldt (pb?1 )

12.5

12.5

12.2

10.8

Events Remaining Cuts By Analysis Channel

Ne + N? ≥ 3 With Quality Cuts Ne forward < 2 / ET > 10 GeV M?? > 5 GeV/c2

13 5 4 0 N/A

42 2 0 N/A N/A

297 5 N/A N/A 0

2475 7 N/A N/A 0

Candidates Background

0 0.8 ± 0.5

0 0.8 ± 0.4

0 0.6 ± 0.2

0 0.1 ± 0.1

TABLE I. Analysis cuts for each of the search channels, showing the number of events left after a cut has been applied. No candidates are seen in any of the four channels. The predicted background per channel is also shown.

14

Events/GeV/c

100

leading lepton

Events/GeV/c

200

second lepton

100

50

0 Events/GeV/c

0

25 50 e or ? pT (GeV/c) Events/GeV

0 150 100 50 0

0

25 50 e or ? pT (GeV/c)

200

third lepton

100

0

0

25 50 e or ? pT (GeV/c)

0

25

50 ET (GeV) /

15

Efficiency (%)

eee 15 10 5 0 50 75 100 W1 mass (GeV/c2)

Efficiency (%)

20

20 ee 15 10 5 0 50 75 100 mass (GeV/c2)

~

~ W

Efficiency (%)

e 15 10 5 0 50 75 100 W1 mass (GeV/c2)

Efficiency (%)

20

20 15 10 5 0 50

1

~

~ W

1

75 100 mass (GeV/c2)

16

~ ~ ~ ~1~2 )Br(W1 → lνZ1 )Br( Z2 → ll-Z1 ) (pb) ~ (W Z

LEP

10

Region Excluded by This Experiment

1

Excluded

by

(b) (c)

(a)

10

-1

Region
40

50

60

70

80 90 100 W1 mass (GeV/c2)

~

17



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