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Fermilab-Pub-99/139-ED0Pub-99-1

Studies of WW and WZ Production and Limits on Anomalous WWγ

and WWZ Couplings

The DØ Collaboration∗

Fermi National Accelerator Laboratory, Batavia, IL 60510

(May 4, 1999)

Abstract

Evidence of anomalous WW and WZ production was sought in pp collisions at a center-of-mass energy of√

s = 1.8TeV. The final states WW (WZ) → µν jet jet + X , WZ → µνee + X and WZ → eνee + X were studied using adata sample corresponding to an integrated luminosity of approximately 90 pb−1. No evidence of anomalous dibosonproduction was found. Limits were set on anomalous WWγ and WWZ couplings and were combined with our previousresults. The combined 95% confidence level anomalous coupling limits for Λ = 2 TeV are −0.25 ≤ ∆κ ≤ 0.39 (λ = 0)and −0.18 ≤ λ ≤ 0.19 (∆κ = 0), assuming the WWγ couplings are equal to the WWZ couplings.

——∗ Authors listed on the following page.Submitted to Physical Review D.

0

Studies of WW and WZ Production and Limits on Anomalous WWγ and WWZ

Couplings

B. Abbott,45 M. Abolins,42 V. Abramov,18 B.S. Acharya,11 I. Adam,44 D.L. Adams,54 M. Adams,28 S. Ahn,27

V. Akimov,16 G.A. Alves,2 N. Amos,41 E.W. Anderson,34 M.M. Baarmand,47 V.V. Babintsev,18 L. Babukhadia,20

A. Baden,38 B. Baldin,27 S. Banerjee,11 J. Bantly,51 E. Barberis,21 P. Baringer,35 J.F. Bartlett,27 A. Belyaev,17

S.B. Beri,9 I. Bertram,19 V.A. Bezzubov,18 P.C. Bhat,27 V. Bhatnagar,9 M. Bhattacharjee,47 N. Biswas,32

G. Blazey,29 S. Blessing,25 P. Bloom,22 A. Boehnlein,27 N.I. Bojko,18 F. Borcherding,27 C. Boswell,24 A. Brandt,27

R. Breedon,22 G. Briskin,51 R. Brock,42 A. Bross,27 D. Buchholz,30 V.S. Burtovoi,18 J.M. Butler,39 W. Carvalho,2

D. Casey,42 Z. Casilum,47 H. Castilla-Valdez,14 D. Chakraborty,47 S.V. Chekulaev,18 W. Chen,47 S. Choi,13

S. Chopra,25 B.C. Choudhary,24 J.H. Christenson,27 M. Chung,28 D. Claes,43 A.R. Clark,21 W.G. Cobau,38

J. Cochran,24 L. Coney,32 W.E. Cooper,27 D. Coppage,35 C. Cretsinger,46 D. Cullen-Vidal,51 M.A.C. Cummings,29

D. Cutts,51 O.I. Dahl,21 K. Davis,20 K. De,52 K. Del Signore,41 M. Demarteau,27 D. Denisov,27 S.P. Denisov,18

H.T. Diehl,27 M. Diesburg,27 G. Di Loreto,42 P. Draper,52 Y. Ducros,8 L.V. Dudko,17 S.R. Dugad,11 A. Dyshkant,18

D. Edmunds,42 J. Ellison,24 V.D. Elvira,47 R. Engelmann,47 S. Eno,38 G. Eppley,54 P. Ermolov,17 O.V. Eroshin,18

H. Evans,44 V.N. Evdokimov,18 T. Fahland,23 M.K. Fatyga,46 S. Feher,27 D. Fein,20 T. Ferbel,46 H.E. Fisk,27

Y. Fisyak,48 E. Flattum,27 G.E. Forden,20 M. Fortner,29 K.C. Frame,42 S. Fuess,27 E. Gallas,27 A.N. Galyaev,18

P. Gartung,24 V. Gavrilov,16 T.L. Geld,42 R.J. Genik II,42 K. Genser,27 C.E. Gerber,27 Y. Gershtein,51

B. Gibbard,48 B. Gobbi,30 B. Gomez,5 G. Gomez,38 P.I. Goncharov,18 J.L. Gonzalez Solıs,14 H. Gordon,48

L.T. Goss,53 K. Gounder,24 A. Goussiou,47 N. Graf,48 P.D. Grannis,47 D.R. Green,27 J.A. Green,34 H. Greenlee,27

S. Grinstein,1 P. Grudberg,21 S. Grunendahl,27 G. Guglielmo,50 J.A. Guida,20 J.M. Guida,51 A. Gupta,11

S.N. Gurzhiev,18 G. Gutierrez,27 P. Gutierrez,50 N.J. Hadley,38 H. Haggerty,27 S. Hagopian,25 V. Hagopian,25

K.S. Hahn,46 R.E. Hall,23 P. Hanlet,40 S. Hansen,27 J.M. Hauptman,34 C. Hays,44 C. Hebert,35 D. Hedin,29

A.P. Heinson,24 U. Heintz,39 R. Hernandez-Montoya,14 T. Heuring,25 R. Hirosky,28 J.D. Hobbs,47 B. Hoeneisen,6

J.S. Hoftun,51 F. Hsieh,41 Tong Hu,31 A.S. Ito,27 S.A. Jerger,42 R. Jesik,31 T. Joffe-Minor,30 K. Johns,20

M. Johnson,27 A. Jonckheere,27 M. Jones,26 H. Jostlein,27 S.Y. Jun,30 C.K. Jung,47 S. Kahn,48 D. Karmanov,17

D. Karmgard,25 R. Kehoe,32 S.K. Kim,13 B. Klima,27 C. Klopfenstein,22 W. Ko,22 J.M. Kohli,9 D. Koltick,33

A.V. Kostritskiy,18 J. Kotcher,48 A.V. Kotwal,44 A.V. Kozelov,18 E.A. Kozlovsky,18 J. Krane,34

M.R. Krishnaswamy,11 S. Krzywdzinski,27 M. Kubantsev,36 S. Kuleshov,16 Y. Kulik,47 S. Kunori,38 F. Landry,42

G. Landsberg,51 A. Leflat,17 J. Li,52 Q.Z. Li,27 J.G.R. Lima,3 D. Lincoln,27 S.L. Linn,25 J. Linnemann,42

R. Lipton,27 A. Lucotte,47 L. Lueking,27 A.L. Lyon,38 A.K.A. Maciel,29 R.J. Madaras,21 R. Madden,25

L. Magana-Mendoza,14 V. Manankov,17 S. Mani,22 H.S. Mao,4 R. Markeloff,29 T. Marshall,31 M.I. Martin,27

R.D. Martin,28 K.M. Mauritz,34 B. May,30 A.A. Mayorov,18 R. McCarthy,47 J. McDonald,25 T. McKibben,28

J. McKinley,42 T. McMahon,49 H.L. Melanson,27 M. Merkin,17 K.W. Merritt,27 C. Miao,51 H. Miettinen,54

A. Mincer,45 C.S. Mishra,27 N. Mokhov,27 N.K. Mondal,11 H.E. Montgomery,27 P. Mooney,5 M. Mostafa,1

H. da Motta,2 C. Murphy,28 F. Nang,20 M. Narain,39 V.S. Narasimham,11 A. Narayanan,20 H.A. Neal,41

J.P. Negret,5 P. Nemethy,45 D. Norman,53 L. Oesch,41 V. Oguri,3 N. Oshima,27 D. Owen,42 P. Padley,54 A. Para,27

N. Parashar,40 Y.M. Park,12 R. Partridge,51 N. Parua,7 M. Paterno,46 B. Pawlik,15 J. Perkins,52 M. Peters,26

R. Piegaia,1 H. Piekarz,25 Y. Pischalnikov,33 B.G. Pope,42 H.B. Prosper,25 S. Protopopescu,48 J. Qian,41

P.Z. Quintas,27 R. Raja,27 S. Rajagopalan,48 O. Ramirez,28 N.W. Reay,36 S. Reucroft,40 M. Rijssenbeek,47

T. Rockwell,42 M. Roco,27 P. Rubinov,30 R. Ruchti,32 J. Rutherfoord,20 A. Sanchez-Hernandez,14 A. Santoro,2

L. Sawyer,37 R.D. Schamberger,47 H. Schellman,30 J. Sculli,45 E. Shabalina,17 C. Shaffer,25 H.C. Shankar,11

R.K. Shivpuri,10 D. Shpakov,47 M. Shupe,20 R.A. Sidwell,36 H. Singh,24 J.B. Singh,9 V. Sirotenko,29 E. Smith,50

R.P. Smith,27 R. Snihur,30 G.R. Snow,43 J. Snow,49 S. Snyder,48 J. Solomon,28 M. Sosebee,52 N. Sotnikova,17

M. Souza,2 N.R. Stanton,36 G. Steinbruck,50 R.W. Stephens,52 M.L. Stevenson,21 F. Stichelbaut,48 D. Stoker,23

V. Stolin,16 D.A. Stoyanova,18 M. Strauss,50 K. Streets,45 M. Strovink,21 A. Sznajder,2 P. Tamburello,38 J. Tarazi,23

M. Tartaglia,27 T.L.T. Thomas,30 J. Thompson,38 D. Toback,38 T.G. Trippe,21 P.M. Tuts,44 V. Vaniev,18

N. Varelas,28 E.W. Varnes,21 A.A. Volkov,18 A.P. Vorobiev,18 H.D. Wahl,25 G. Wang,25 J. Warchol,32 G. Watts,51

M. Wayne,32 H. Weerts,42 A. White,52 J.T. White,53 J.A. Wightman,34 S. Willis,29 S.J. Wimpenny,24

J.V.D. Wirjawan,53 J. Womersley,27 D.R. Wood,40 R. Yamada,27 P. Yamin,48 T. Yasuda,40 P. Yepes,54 K. Yip,27

C. Yoshikawa,26 S. Youssef,25 J. Yu,27 Y. Yu,13 B. Zhang,4 Z. Zhou,34 Z.H. Zhu,46 M. Zielinski,46 D. Zieminska,31

A. Zieminski,31 V. Zutshi,46 E.G. Zverev,17 and A. Zylberstejn8

(DØ Collaboration)1Universidad de Buenos Aires, Buenos Aires, Argentina

2LAFEX, Centro Brasileiro de Pesquisas Fısicas, Rio de Janeiro, Brazil

1

3Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil4Institute of High Energy Physics, Beijing, People’s Republic of China

5Universidad de los Andes, Bogota, Colombia6Universidad San Francisco de Quito, Quito, Ecuador

7Institut des Sciences Nucleaires, IN2P3-CNRS, Universite de Grenoble 1, Grenoble, France8DAPNIA/Service de Physique des Particules, CEA, Saclay, France

9Panjab University, Chandigarh, India10Delhi University, Delhi, India

11Tata Institute of Fundamental Research, Mumbai, India12Kyungsung University, Pusan, Korea

13Seoul National University, Seoul, Korea14CINVESTAV, Mexico City, Mexico

15Institute of Nuclear Physics, Krakow, Poland16Institute for Theoretical and Experimental Physics, Moscow, Russia

17Moscow State University, Moscow, Russia18Institute for High Energy Physics, Protvino, Russia19Lancaster University, Lancaster, United Kingdom

20University of Arizona, Tucson, Arizona 8572121Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720

22University of California, Davis, California 9561623University of California, Irvine, California 92697

24University of California, Riverside, California 9252125Florida State University, Tallahassee, Florida 32306

26University of Hawaii, Honolulu, Hawaii 9682227Fermi National Accelerator Laboratory, Batavia, Illinois 60510

28University of Illinois at Chicago, Chicago, Illinois 6060729Northern Illinois University, DeKalb, Illinois 6011530Northwestern University, Evanston, Illinois 6020831Indiana University, Bloomington, Indiana 47405

32University of Notre Dame, Notre Dame, Indiana 4655633Purdue University, West Lafayette, Indiana 47907

34Iowa State University, Ames, Iowa 5001135University of Kansas, Lawrence, Kansas 66045

36Kansas State University, Manhattan, Kansas 6650637Louisiana Tech University, Ruston, Louisiana 71272

38University of Maryland, College Park, Maryland 2074239Boston University, Boston, Massachusetts 02215

40Northeastern University, Boston, Massachusetts 0211541University of Michigan, Ann Arbor, Michigan 48109

42Michigan State University, East Lansing, Michigan 4882443University of Nebraska, Lincoln, Nebraska 6858844Columbia University, New York, New York 1002745New York University, New York, New York 10003

46University of Rochester, Rochester, New York 1462747State University of New York, Stony Brook, New York 11794

48Brookhaven National Laboratory, Upton, New York 1197349Langston University, Langston, Oklahoma 73050

50University of Oklahoma, Norman, Oklahoma 7301951Brown University, Providence, Rhode Island 02912

52University of Texas, Arlington, Texas 7601953Texas A&M University, College Station, Texas 77843

54Rice University, Houston, Texas 77005

Evidence of anomalous WW and WZ production was sought in pp collisions at a center-of-massenergy of

√s = 1.8 TeV. The final states WW (WZ) → µν jet jet + X, WZ → µνee + X and

WZ → eνee + X were studied using a data sample corresponding to an integrated luminosity ofapproximately 90 pb−1. No evidence of anomalous diboson production was found. Limits were set onanomalous WWγ and WWZ couplings and were combined with our previous results. The combined95% confidence level anomalous coupling limits for Λ = 2 TeV are −0.25 ≤ ∆κ ≤ 0.39 (λ = 0) and−0.18 ≤ λ ≤ 0.19 (∆κ = 0), assuming the WWγ couplings are equal to the WWZ couplings.

2

I. INTRODUCTION

The gauge theory of the electroweak interactions con-tains a striking feature. Unlike the electrically neutralphoton in quantum electrodynamics (QED), the weakvector bosons carry weak charge. Consequently, whereasin QED there are no photon-photon couplings, the weakvector bosons interact amongst themselves through thetrilinear and quartic gauge boson vertices.

A formalism has been developed to describe the WWγand WWZ vertices for the most general gauge bosonself-interactions [1,2]. The Lorentz invariant effective La-grangian for the gauge boson self-interactions containsfourteen dimensionless couplings, seven each for WWγand WWZ:

LWWV /gWWV = igV1

(

W †µνWµV ν − W †

µVνWµν)

+iκV W †µWνV µν + i

λV

M2W

W †λµWµ

ν V νλ

−gV4 W †

µWν(∂µV ν + ∂νV µ)

+gV5 ǫµνρα

(

W †µ

↔

∂ ρ Wν

)

Vα

+iκV W †µWν V µν +

iλV

M2W

W †λµWµ

ν V νλ,

where Wµ denotes the W− field, Wµν = ∂µWν − ∂νWµ,

Vµν = ∂µVν − ∂νVµ, Vµν = 12ǫµνραV ρα, and (A

↔

∂ µ B) =A(∂µB) − (∂µA)B, V = γ and Z, and MW is the massof the W boson. The overall coupling parameters gWWV

are gWWγ = −e and gWWZ = −e cotθw, as in the stan-dard model (SM), where e and θw are the positron chargeand the weak mixing angle. The couplings λV and κV

conserve C and P . The couplings gV4 are odd under CP

and C, gV5 are odd under C and P , and κV and λV

are odd under CP and P . In the SM, all the couplingsare zero at tree level with the exception of gV

1 and κV

(gγ1 = gZ

1 = κγ = κZ = 1), and ∆κV and ∆gZ1 are de-

fined as κV −1 and gZ1 −1, respectively. Electromagnetic

gauge invariance restricts gγ1 , gγ

4 , and gγ5 to the SM values

of 1, 0, and 0. The CP -violating WWγ couplings λγ andκγ have been tightly constrained by measurements of the

neutron electric dipole moment to |κγ |, |λγ | < 10−3 [3].With non-SM coupling parameters, the amplitudes for

gauge boson pair production grow with energy, eventu-ally violating tree-level unitarity. The unitarity violationis avoided by parameterizing the anomalous couplingsas dipole form factors with a cutoff scale, Λ. Then theanomalous couplings take a form, for example,

∆κ(s) =∆κ

(1 + s/Λ2)2,

where s is the invariant mass of the vector boson pairand ∆κ is the coupling value at the low energy limit [4].Λ is physically interpreted as the mass scale where the

new phenomenon which is responsible for the anomalouscouplings would be directly observable.

Direct tests of the trilinear couplings are provided bye+e− and pp colliders through production of gauge bosonpairs, in particular by e+e− → W+W−, Zγ, and ZZand by pp → W±γ, W+W−, W±Z, Zγ, and ZZ. Theexperiments seek to measure, or otherwise place limitson, trilinear couplings and to retain sensitivity to theappearance of new physical phenomena. The signaturefor anomalous trilinear couplings is an excess of gaugeboson pairs, particularly for large values of the invariantmass of the gauge boson pair and for large values of gaugeboson transverse momentum pT .

Limits on these couplings are often obtained underthe assumption that the WWγ and WWZ couplingsare equal (gγ

1 = gZ1 , ∆κγ = ∆κZ , and λγ = λZ). An-

other set of parameters, αBφ, αWφ, and αW , is simi-larly motivated by SU(2)L × U(1)Y gauge invariance.These couplings are linear combinations of λV , ∆κV ,and ∆gZ

1 such that αBφ = ∆κγ − ∆gZ1 cos2 θw, αWφ =

∆gZ1 cos2 θw, and αW = λγ with the constraints that

∆κZ = −∆κγ tan2 θw + ∆gZ1 and λγ = λZ . Adding the

additional constraint that αBφ = αWφ yields [5] the HISZrelations used by the DØ and CDF collaborations.

The DØ collaboration has previously performed sev-eral searches for anomalous WWγ and WWZ couplings.Studies [6,7] of pp → Wγ +X have shown that the trans-verse energy spectrum of the photons agreed with thatexpected from SM production. Searches [8,9] for an ex-cess of pp → WW +X , where the W bosons each decayedto ℓν (ℓ = e or µ), yielded events which matched the SMprediction. Further, the pT spectrum of the charged lep-tons agreed [9] with the prediction. Studies [10,11] of theprocesses pp → WW +X and pp → WZ +X , where oneW boson decayed to an electron or positron and the cor-responding antineutrino or neutrino and the other vectorboson decayed to a quark-antiquark pair manifested asjets, yielded no excess of events and a W boson trans-verse energy spectrum which matched the expected back-ground plus SM signal. Limits on anomalous WWγ andWWZ couplings were derived from each of these analy-ses. Several [6,8,10] of these analyses were presented indetail in Ref. [12]. The results of all of these analyses werecombined [13], using the method described in Ref. [12],to form our most restrictive limits on anomalous WWγand WWZ couplings.

Limits on the WWγ couplings have been set by theUA2 and CDF collaborations from the properties ofW + γ events [14,15] and by the L3 Collaboration [16]from the rate of single W boson production at

√s = 172

GeV. Both the WWZ and WWγ couplings have beenstudied by several experiments. CDF has searched foranomalous WW and WZ production [17,18] and the fourexperiments at the LEP e+e− collider have studied theproperties of WW events [19–26].

In this paper two new analyses resulting from a study

3

of pp collisions at a center-of-mass energy of√

s = 1.8TeV are presented. The collisions were recorded at DØduring the 1994–1995 and 1996 collider runs of the Fer-milab Tevatron.

The first analysis is a search for WZ production whichprovides a test of anomalous couplings unique among thegauge boson pair analyses. WZ production is sensitiveonly to the WWZ couplings, not the WWγ couplings. Inthis analysis the collisions were searched for WZ eventswhere the Z boson decayed to ee and the W boson de-cayed to either eν or µν. The expected SM WZ signaland the background were approximately equal in size andboth were expected to be small. The number of eventsobserved was compared with that expected from anoma-lous WZ production in the presence of background to setupper limits on anomalous WWZ couplings.

The second analysis is a search for anomalous WWand WZ (WW/WZ) production, similar to those ofRefs. [10,11], using the decay signature W → µν, W/Z →hadronic jets. Because SM WW and WZ productionwas swamped by backgrounds from other sources of µνjjevents, the analysis was sensitive only to anomalous vec-tor boson pair production. The pT spectrum of the µνsystem was compared to that expected from anomalousWW and WZ production plus the background, and lim-its on anomalous WWZ and WWγ couplings were pro-duced.

The paper is arranged so that the subsequent two sec-tions present elements common to the two analyses: thedetector and particle identification. The fourth sectionis a description of the WZ → ℓℓℓν + X search and limitson anomalous WWZ couplings. The next section de-scribes the WW/WZ → µνjj + X analysis and limitson anomalous WWZ and WWγ couplings. The sixthsection contains a summary of the results of combiningthe anomalous coupling limits of these two analyses withthose of our previous publications, producing the mostrestrictive anomalous WWγ and WWZ coupling limitsavailable to date from this experiment. Finally, the lastsection contains the conclusion and summary of the re-sults presented in this paper.

II. DETECTOR

The DØ detector consisted of four main systems: anon-magnetic inner tracking system, a liquid-argon ura-nium calorimeter, a muon spectrometer, and a triggersystem. The detector is briefly described in this sec-tion. A detailed description of the detector is availablein Ref. [27]. The tracker, calorimeter, and muon systemare shown in Fig. 1.

A non-magnetic central tracking system, composed ofcentral and forward drift chambers, provided directionalinformation for charged particles and is used in this anal-ysis to discriminate between electrons and photons, and

in muon identification.Particle energies were measured by a liquid-argon ura-

nium sampling calorimeter that was divided into threecryostats. The central calorimeter (CC) covered pseudo-rapidity [28] |η| < 1.1, and the end calorimeters (EC)covered 1.1 < |η| < 4.4. The calorimeter was trans-versely segmented into projective towers with ∆η×∆φ =0.1 × 0.1, where φ is the azimuthal angle. The thirdlayer of the electromagnetic (EM) calorimeters, wherethe maximum energy deposition from EM showers wasexpected to occur, was segmented more finely into cellswith ∆η × ∆φ = 0.05 × 0.05. The scintillator-based in-tercryostat detectors (ICD’s), which improved the en-ergy resolution for jets that straddled the central andend calorimeters, were inserted into the space betweenthe cryostats. Thus, jet identification was performed inthe whole calorimeter without any gap in pseudorapidity.Electron identification was performed for EM clusterswith pseudorapidity |η| ≤ 2.5; but the boundary betweenthe CC and EC cryostats resulted in a gap spanning theregion 1.1 ≤ |η| ≤ 1.5.

The muon spectrometer consisted of solid-iron toroidalmagnets and sets of proportional drift tubes (PDT’s). Itprovided identification of muons and determination oftheir trajectories and momenta. It consisted of threelayers: a layer with four planes of PDT’s, located be-tween the calorimeter and the toroid magnets; and twolayers, each with three planes of PDT’s, located outsidethe toroid magnets. Figure 2 shows the geometric ac-ceptance of the muon detector for the region |η| ≤ 1 asdetermined from a Monte Carlo simulation of the detec-tor. The muon momentum p was determined from itsdeflection angle in the magnetic field of the toroid. Themomentum resolution was limited by multiple scatteringin the calorimeter and toroid, knowledge of the magneticfield integral, and the accuracy of the deflection anglemeasurement.

A multi-level, multi-detector trigger system [12,27] wasused for selecting interesting events and recording themto tape. A coincidence between hits in two hodoscopesof scintillation counters (Level 0), centered around thebeampipe, was required to register the presence of aninelastic collision. These counters also served as the lu-minosity monitor for the experiment. The Level 1 andLevel 1.5 triggers were programmable hardware triggerswhich made decisions based on combinations of detector-specific algorithms. The Level 2 trigger was a farm of 48VAX 4000/60 and 4000/90 computers which filtered theevents based on reconstruction of the information avail-able from the front-end electronics.

III. PARTICLE IDENTIFICATION

The analyses described in this paper rely on the detec-tor’s ability to identify electrons, muons, hadronic jets,

4

and the undetected transverse energy due to neutrinos.A brief description of the particle identification criteriais presented in this section. A more detailed descrip-tion of these particle identification criteria is available inRef. [12].

A. Electron Identification

Electron candidates were identified using informationfrom the calorimeters and tracking detectors. Electroncandidates were formed from clusters, identified using anearest-neighbor algorithm, with more than 90% of theirenergy in the EM layers of the calorimeter. The EM clus-ters had to fall within the CC (|η| < 1.0) or either EC(1.5 < |η| < 2.5). Electrons had to be isolated, had tohave a shower shape consistent with that from test beammeasurements, and had to have either a track that closelymatched the position of the shower centroid (“tight” se-lection criteria) or drift chamber hits consistent with thepassage of a charged particle within an azimuthal roadof width ∆φ = 15 (30) milliradians for CC (EC) EMclusters (“loose” selection criteria).

The efficiency for selecting electrons with the selectioncriteria described above was calculated using Z → eedecays. The efficiencies for each η region and electrondefinition are shown in Table I. The energy resolutionwas σ(E)/E = 14%/

√

E(GeV)⊕0.3%⊕14%/E(GeV) for

electrons in the CC and σ(E)/E = 15.7%/√

E(GeV) ⊕0.3%⊕ 29%/E(GeV) for electrons in the EC, where “⊕”indicates addition in quadrature.

B. Muon Identification

Muon candidates were tracks in the muon chamberswhich survived a number of reconstruction quality cuts.A muon was required to lie within the central region(|η| < 1.0). A muon had to pass through a region of themuon toroid with sufficient magnetic field (

∫

Bdl > 2.0Tesla-meters). The energy deposited along the muontrack in the calorimeter had to be at least that expectedfrom a minimum-ionizing particle which on average de-posits ∼ 1 GeV. The impact parameter of the muon withrespect to the interaction point had to be less than 20cm. The muon track was refitted with the timing, t0, ofthe muon track with respect to the collision as a floatingparameter. It was required that t0 be consistent with amuon originating from the interaction. A slightly differ-ent t0 cut was used in the two analyses due to the differentnature of the backgrounds. Lastly, the muon had to beseparated by ∆Rµ ≡

√

(∆η)2 + (∆φ)2 ≥ 0.5 from thenearest jet in the event. The muon reconstruction effi-ciency in the WZ → µνee (WW/WZ → µνjj) analysisfor muons with |ηµ| < 1 was 0.701 ± 0.031 (0.680+0.041

−0.080)excluding losses due to the geometric acceptance of the

muon detector. The muon momentum resolution wasσ( 1

p) = 0.18(p− 2)/p2 ⊕ 0.003 (p in GeV/c).

C. Jet Identification and Missing Energy

Jets were identified [12] as clusters of calorimeter tow-ers within a cone centered on the highest ET tower.For the analyses described here, a cone size of R ≡√

(∆η)2 + (∆φ)2 = 0.5 was used. The energy de-posited by the jet in the electromagnetic and hadroniccalorimeters had to be consistent with that of an ordi-nary jet, thus suppressing the backgrounds from isolatednoisy calorimeter cells and accelerator losses. These jetidentification criteria have an efficiency of 0.96 ± 0.01per jet. The jet energy resolution depended on thejet pseudorapidity and was approximately σ(E)/E =80%/

√

E(GeV).The primary sources of missing transverse energy in-

cluded neutrinos, which escaped undetected, and the en-ergy imbalance due to the resolution of the calorimeterand muon system. Two calculations of missing transverseenergy were made. The missing transverse energy whichwas calculated from the energy deposited in the calorime-ter is referred to as /Ecal

T . The missing energy which wascalculated from the energy deposited in the calorimeterand was corrected for muons passing some loose qualitycuts is referred to as /ET .

IV. SEARCH FOR WZ → TRILEPTONS

A search for WZ production was performed in the eνeeand µνee decay modes, taking advantage of the unusualsignature consisting of three charged high-ET leptons andthe missing transverse energy due to the high-ET neu-trino.

A. Trigger and Data Sample

The Level 1 trigger used for this study required twoEM calorimeter trigger towers (∆η × ∆φ = 0.2 × 0.2)with ET > 10 GeV. The Level 2 trigger required twoclusters of EM trigger towers which had ET > 20 GeVand passed Level 2 isolation and shower shape cuts. Theefficiency of the trigger was measured as a function of thereconstructed electron ET and found to be greater than99% for a reconstructed ET > 25 GeV. The integratedluminosity of the data sample was 92.3 ± 5.0 pb−1. Theluminosity determination is described in Ref. [29].

5

B. Event Selection Criteria

WZ → eνee events were required to have two high-ET electrons consistent with a Z boson decay, and athird electron and /ET consistent with a W boson de-cay. Specifically, at least one electron was required tosatisfy the tight selection criteria and another two wererequired to satisfy the tight or loose selection criteria (asdefined in Section III A). A tight electron and one of theother electrons were required to have ET > 25 GeV andthe third electron to have ET > 10 GeV. It was requiredthat /Ecal

T > 15 GeV. The invariant mass of two of theelectrons had to be within the range 81 < Mi,j < 101GeV/c2, as expected for the decay of a Z boson. Thetransverse mass

MT (eν) =√

2EeT /Ecal

T (1 − cos(φe − φν))

calculated using the ET of the other electron and the/Ecal

T was required to be MT (eν) > 30 GeV, as expectedfor the decay of a W boson. These criteria were checkedfor all three combinations of electrons. One event wasfound which passed all the selection criteria. The pa-rameters [30] of this event are described in the appendix.

WZ → µνee events were required to have two high-ET

electrons as expected for a Z boson decay, and a muonand /ET consistent with a W boson decay. Specifically,at least one electron was required to satisfy the tightselection criteria and another was required to satisfy thetight or loose selection criteria. Both electrons had tohave ET > 25 GeV. Instead of the 10 GeV third electronof the eνee search, a muon with pT > 15 GeV/c wasrequired. Finally, it was required that /ET > 15 GeV. Noevents passed these selection criteria.

C. Background Expected

The trilepton plus missing transverse energy signaturedemanded by the event selection has no known significantsources other than WZ production and backgrounds dueto objects misidentified as leptons.

In the eνee channel the largest background was ex-pected to come from Z + jet events with Z → ee andwhere a jet mimicked an additional electron. This back-ground was estimated using data. Events with two elec-tron candidates and one or more jets were selected fromthe same data sample used in the event selection. Thekinematic event selection criteria were applied treatingeach jet as the third electron. The probability for ajet to mimic a tight or loose electron was determinedfrom a sample of multijet events and was parameter-ized by a linear function of jet ET for jets with ET

less than ∼ 150 GeV, as given in Table II. The back-ground was then the number of ee + jet events timesthe probability of a jet mimicking the third (tight or

loose) electron. This background was estimated to be0.38 ± 0.07(stat) ± 0.11(syst) events. The size of thestatistical uncertainty was determined by the statisticsof the ee+ jets sample. The systematic uncertainty wasdominated by the 25% uncertainty in the probability fora jet to mimic a tight or loose electron. This latter un-certainty was due, in large part, to the uncertainty onthe amount of direct photons in the multijet sample. Across check based on a data sample of events enrichedwith highly EM jets which failed the electron selectioncriteria gave 0.42+0.41

−0.26 events for this background.In the µνee channel there were two contributions to

the background, one from events with two electrons anda jet which produced an isolated muon and one fromevents with an electron, a muon, and a jet which mim-icked an electron. Data-based methods of calculating thebackground were used to estimate both of these contri-butions to the background.

To calculate the ee+jet event background, events withtwo electrons and a central jet were selected (this wascalled the “fake” sample). Each event was required topass all selection criteria except that the jet was onlyrequired to pass the muon fiducial and kinematic selec-tion. The number of events was then multiplied by theprobability of the jet producing an isolated muon, thisprobability having been determined using two methods.The probability (per jet) of finding an isolated muon ina sample of multijet events with ET (jet) > 15 GeV wasfound to be 1.5 × 10−5. The number of events expectedfrom this background was ≤ 0.002. On the other hand,a fraction of the ee + jet events contained heavy quark(b/c) jets. Assuming that all of the jets in the fake sampleare heavy quark jets, a heavy-quark-enhanced fake ratewas used to obtain an upper limit for this background.The probability of a jet mimicking a muon from a heavyquark (b/c) jet was found by requiring a muon (isolatedor non-isolated) in the opposite hemisphere from the iso-lated muon in multijet events. This gave a heavy-quark-enhanced fake rate of 2.5 × 10−4, resulting in an upperlimit of Nbkg = 0.022 ± 0.004 events. When settinglimits on the cross section and coupling parameters, asmaller background estimate gives a more conservativelimit. Therefore the lower estimate (≤ 0.002 events) wasused in lieu of the larger (0.022 events).

The second background (eµ+jet events) was calculatedusing events collected with a different trigger which re-quired one EM object with ET > 20 GeV and /ET > 20GeV. Events were selected which had an isolated muon,one or more jets, and a tight or loose electron. All eventselection cuts were applied with the exception of the trig-ger. The number of background events was then found bysumming the ET -dependent probability for a jet to havemimicked an electron for each event which passed theevent selection criteria, accounting correctly for eventswhich contained more than one jet and the difference inthe integrated luminosities between the two triggers. The

6

total number of background events expected from eµ+ jetevents was found to be 0.118 ± 0.018(stat) ± 0.035(syst).Again, the systematic error is due to the uncertainty inthe probability for a jet to mimic an electron.

The total background to WZ → trileptons was 0.50±0.17 events.

D. Efficiency Estimate

The efficiency estimate was made using a leading-order Monte Carlo (MC) event generator [2] which alsocould simulate the effects of anomalous couplings. TheMRSD-′ parton distribution functions [31] were used.To correct for the effects of higher-order QCD processeswhich contribute to WZ production, the resulting crosssection was increased by a k-factor of 1.34 [2] and theWZ system was given a transverse boost according to thedistribution produced by the pythia Monte Carlo [32]simulation of SM WZ production. A parameterized de-tector simulation was used to account for the acceptanceof the detector, the effects of detector resolution on themeasurements of charged leptons and /ET , and the length(σ ∼ 30 cm) of the pp collision region along the beam di-rection.

For SM WZ production, the detection efficiency in theeνee and µνee channels was found to be (16.9 ± 1.4)%and (11.5 ± 1.4)%, respectively. For a SM cross sectionof 2.6 pb [33], the (W → ℓν) × (Z → ee) branchingfractions [34], and an integrated luminosity of 92.3± 5.0pb−1, the expected number of events in the eeeν andeeµν channels was 0.146 ± 0.002(stat) ± 0.012(syst) and0.099± 0.001(stat)± 0.009(syst), respectively. The smallstatistical uncertainties reflected the large number of MCevents generated and processed through the detector sim-ulation. The systematic error included the uncertaintiesin the luminosity (5.3%), the particle identification effi-ciency (0.7%), the trigger efficiency (2%), the branchingfraction (3.7%), and the MC cross section due to thechoice of the parton distribution function and Q2 scale(5%). The total expected signal from SM WZ produc-tion was 0.25 ± 0.02 events. The results are summarizedin Table III.

E. WZ Production Cross Section Limit

The 95% confidence level (C.L.) upper limit on theWZ cross section is estimated based on one observedevent and a subtraction of the expected background of0.50±0.17 events. Poisson-distributed numbers of eventswere convoluted with Gaussian uncertainties in the effi-ciency and background. For WZ production, the 95%C.L. upper limit on the cross section was 47 pb, consis-tent with, but much larger than, the SM prediction.

F. Limits on Anomalous WWZ Couplings

The event generator [2] and parameterized detectorsimulation were used, in a manner identical to that de-scribed above, to find the efficiency and expected numberof events in the case of hypothetical anomalous WZ cou-plings. A grid in the λZ–∆gZ

1 plane was used. Once theprobability for observing one event was determined [30]for each point in the grid, limits on the anomalous cou-plings were made. The limits were found by taking thelogarithm of the likelihood and identifying the contourin λZ − ∆gZ

1 around the point of maximum of the loga-rithm of the likelihood (Lmax) where L = Lmax − δ. Toset a 95% C.L. limit in one dimension, the contour wasevaluated at δ = 1.92. To set a 95% C.L. limit in twodimensions (allowing two anomalous couplings to vary atthe same time), the contour was evaluated at δ = 3.00.

The value of the form factor scale Λ was chosensuch that the coupling limit was less than the unitar-ity limit [35]. The one-dimensional 95% C.L. couplinglimits and unitarity limits as a function of Λ for each ofthe three coupling parameters are shown in Fig. 3.

This analysis was most sensitive to the parameters λZ

and ∆gZ1 . Setting Λ = 1 TeV, the one-dimensional 95%

C.L. limits from the eνee and µνee channels are

|∆gZ1 | < 1.63

|λZ | < 1.42

when all other parameters are held at their SM values.The two-dimensional 95% C.L. contour limits for Λ = 1TeV are shown in Fig. 4 for the eνee and µνee datacombined.

V. SEARCH FOR ANOMALOUS WW AND WZPRODUCTION

The 1994–1995 data were searched for anomalousWW/WZ production in events with the signature: high-pT muon; large /ET ; and at least two jets (µνjj).

A. Trigger and Data Sample

The Level 1 trigger consisted of a muon candidate inthe central region and at least 5 GeV deposited in ahadronic trigger tower (∆η × ∆φ = 0.2 × 0.2). As themuon scintillation counters became available during thecollider run they were added to the Level 1 trigger insuch a way as to veto out-of-time muons, such as thosethat originated from cosmic rays.

The Level 2 trigger required a muon with pT > 10GeV/c, as determined by the muon pattern recognitionalgorithm taken from the reconstruction program. A

7

jet was required with ET > 15 GeV within the region|η| < 2.5. The jets were identified by a cone algorithmwhich summed ET ’s of calorimeter towers in cones ofR = 0.7. The efficiency of the jet part of the Level 1 andLevel 2 triggers was measured as a function of the recon-structed jet ET in three separate pseudorapidity bins bycomparing the results of the single-muon trigger with thesingle-muon plus jet trigger for events which contained asingle jet. Figure 5 shows the jet trigger efficiency as afunction of jet ET for the pseudorapidity region |η| < 1.0.The jet trigger efficiency reached a plateau at jet ET ofapproximately 40 GeV. The efficiency was parameterizedusing an error function. The curve shown in Fig. 5 is theresult of that fit. The results in the other two pseudora-pidity regions were similar. For SM Monte Carlo eventswhich passed all of the selection criteria, the efficiency ofthe jet part of the trigger was 0.927 ± 0.007. An alter-nate fit with a plateau at 100% increased this efficiencyby 0.012 and that was taken as a systematic uncertainty.The efficiency of the muon component of the trigger was0.707± 0.018. The integrated luminosity [29] of the datasample was 80.7 ± 4.3 pb−1.

B. Event Selection Criteria

The signature of the muon + jets channel consisted ofan isolated high-pT muon from the W boson decay and aminimum of two jets from a W or Z boson decay. We didnot differentiate between the two processes W → jj andZ → jj due to the dijet mass resolution of the calorime-ter. Single muon events with the following characteristicswere selected. The muon was within the central region,which corresponded approximately to |η| < 1, and hadtransverse momentum pµ

T ≥ 20 GeV/c. A /ET of at least20 GeV was required in each event. Demanding a trans-verse mass MT (µν) > 40 GeV/c2, where

MT (µν) =√

2EµT /ET (1 − cos(φµ − φν)),

completed the kinematic selection defining the decay ofa W boson candidate. Next, the candidates had to con-tain at least two jets (|η| < 2.5) with ET ≥ 20 GeV.The invariant mass of the two highest ET jets had to bebetween 50 and 110 GeV/c2 as expected for the decayof a W or Z boson. Figure 6 displays the distributionof the invariant mass of the two highest ET jets in the372 events which remained in the sample after all selec-tion criteria, except for the dijet mass selection, had beenapplied.

Application of the above cuts led to a final data sam-ple of 224 events. The pT (µν) distribution for theseevents is shown in Fig. 7. The distribution indicatesabsence of events at pT (µν) > 150 GeV/c. The Wboson candidate with the highest transverse energy hadpT (µν) = 141 GeV/c.

C. Background Expected

There were two major sources of background to theWW/WZ → µνjj production: W + ≥ 2 jets with W →µν; and QCD multijet events where one of the jets wasaccompanied by a muon which was misidentified as anisolated muon and where there was significant /ET . Thelatter background could have arisen from b-quark pairproduction, for instance. Contributions from other back-grounds such as: tt production with subsequent decay toW+bW−b followed by W → µν; WW/WZ productionwith W → τν followed by τ → µνν; ZX → µµX , whereone of the muons was missing; and ZX → ττX withτ → µνν, were small or negligible.

The QCD multijet background was estimated using abackground enriched data sample. This technique wassimilar to that used in our previous analysis [36]. Theprobability for a jet with a muon to be misidentified asan isolated muon was determined from the ratio of thenumber of events containing an isolated muon, at leastone jet, and /ET less than 20 GeV to the number of eventswhich contained a muon which failed the jet isolation re-quirement (but otherwise passed the muon identificationcuts), two or more jets, and /ET less than 20 GeV. Thisprobability was 0.041±0.007. Then the number of eventswhich passed all of the selection criteria of the signal ex-cept for the muon-jet isolation requirement, again appliedin reverse so as to form a sample complementary to thesignal, was counted. This provided the sample of eventsfor which misidentification of a non-isolated muon as anisolated muon would have created a false signal. Therewere 2567 such events. Thus the QCD multijet back-ground was 105 ± 19 (stat) events. The QCD multijetbackground was also calculated for events which passedall the selection criteria for the signal except for the dijetinvariant mass selection, which was applied in reverse.This number was necessary for performing a backgroundsubtraction to the data in the out-of-mass cut region inorder to calculate a normalization factor for the W+ ≥ 2jets background. The QCD multijet background in theout-of-mass cut region was 55 ± 14 (stat) events.

The W + ≥ 2 jets background was estimated usingthe vecbos [37] event generator, with Q2 = (pj

T )2, fol-lowed by parton fragmentation using the herwig [38]package and a detailed geant-based [39] simulation ofthe detector. Normalization of the W+ ≥ 2 jets back-ground was determined by comparing the number ofevents expected from the vecbos estimate to the numberof candidate events outside the dijet mass window, afterthe QCD multijet contribution had been subtracted. Thecontribution from this background was calculated to be117 ± 24 (stat) events. A small component of the back-ground, due to Z + ≥ 2 jets with an unreconstructedmuon which mimicked the /ET , was accounted for in thisprocedure because of the kinematic similarity to W boson

8

decay.Among the other backgrounds, the only non-negligible

contribution arose from tt → W+bW−b decays. This wasestimated using a Monte Carlo sample produced similarlyto that of the W + ≥ 2 jets background sample. The ttbackground, calculated assuming a cross section of 5.5±1.8 pb [40], amounted to 2.7 ± 1.2 events.

The total expected background was 224 ± 31 (stat)events. The number of observed events (224) was consis-tent with the background, and was much larger than thepredicted SM WW/WZ signal (discussed in the next sec-tion). The systematic uncertainties in the QCD multijetbackground and the W+ ≥ 2 jets background were corre-lated because of the common uncertainty in the jet energyscale and because of the background subtraction carriedout in the normalization procedure when the W+ ≥ 2jets background was determined. As a cross check, theconsistency between the background estimate and thenumber of observed events was verified for variationsof the event selection criteria. The systematic uncer-tainties for the background estimation were: dijet masswindow selection (13.4%); muon isolation (11.7%); jetenergy scale (7.8%); missing transverse energy selection(7.2%); and W boson transverse mass selection (4.3%).The total systematic uncertainty in the background was46 events and the total uncertainty in the backgroundwas 56 events.

The contributions from all background sources areshown in Table IV. The estimates in the table for thecomponents of the background include statistical uncer-tainties only. Figure 6 also displays the invariant massof the two highest-ET jets from the expected backgroundwith all selection criteria, except for the dijet invariantmass selection, applied. The final distributions of the sig-nal and the sum of backgrounds are plotted as a functionof pT (W ) in Fig. 7.

D. WW/WZ Signal Estimate

The efficiency for detecting WW and WZ events, forboth SM and anomalous couplings, was determined usinga leading-order event generator [2] and a parameterizedsimulation of the detector. The MRSD-′ parton distri-butions [31] and a k-factor of 1.34 [2] were used in esti-mating the WW/WZ cross section. In order to simulatethe kinematics associated with higher-order productionprocesses, the diboson decay products were boosted inthe direction opposite to the hadronic recoil accordingto the ET distribution provided by pythia [32] for SMWW production. The efficiency was 2.5% lower whenthis boost was turned off, and half of this difference wastaken as the fractional systematic uncertainty. The in-teraction points were selected around the center of thenominal collision point (z=0) from a Gaussian distribu-tion with σ = 30 cm.

The muon fiducial acceptance was determined from ageant-based [39] detector model and is shown in Fig. 2.

The jets from a high-pT W or Z boson decay mayhave been close enough to overlap and have poorly re-constructed energies, or they may have been completelymerged into one jet. Therefore, the efficiencies of thejet selection and dijet mass selection depended on theboson’s pT . SM WW events, generated using pythia

Monte Carlo and the geant-based detector model, wereused to determine this efficiency as a function of pT (µν).The results were incorporated into the parameterized de-tector simulation. Figure 8 shows the efficiency as a func-tion of pT (µν) for events which passed the rest of theevent selection criteria. The efficiency was low for low-pT W boson events because of the jet ET threshold of 20GeV. It peaked at 63% for pT (µν) = 200 GeV/c and fellfor higher pT because of jet merging. The uncertainty inthe jet energy scale corrections led to a systematic uncer-tainty in the efficiency for W and Z boson identificationof 3%.

The kinematic efficiencies for SM WW and WZ detec-tion were 0.073 ± 0.002(stat) ± 0.003(syst) and 0.067 ±0.002(stat) ± 0.010(syst), respectively, where the addi-tional systematic uncertainty originates from differencesbetween the acceptances calculated with the parameter-ized detector simulation and the acceptances calculatedusing pythia and geant due to the jet reconstructionefficiency parameterization. Folding in the uncertaintiesdue to the model of the jet trigger, the jet energy scale,and in the initial diboson boost, the systematic uncer-tainties in the kinematic efficiency amounted to 6.7% and15.8% of the WW and WZ detection efficiency. Thus,the total efficiencies for SM WW and WZ productionwere 0.0351+0.0033

−0.0048 and 0.0322+0.0055−0.0064, respectively. The

efficiency was slightly higher for simulated WW and WZproduction with anomalous WWγ and/or WWZ cou-plings because the bosons originated at higher averagepT . For instance, for WW events produced with Λ = 2.0TeV, the total efficiency was 0.038+0.004

−0.005 for the case

λ = 1.0 and ∆κ = 0.0, and 0.043+0.004−0.006 for the case

λ = 2.0 and ∆κ = 2.0.The predicted cross section [2] for SM WW (WZ) pro-

duction is 10.1 (2.6) pb. A 5% systematic uncertaintyin this originates from the variation of the cross sec-tion depending on the set of parton distributions usedin the event generation. The branching fractions [34]for W → µν and W → jets or Z → jets lead to overallbranching fractions of 0.1412±0.0086 and 0.0727±0.0042,respectively. Therefore, with an integrated luminosity of80.7±4.3 pb−1, 4.04+0.54

−0.68 WW events and 0.49+0.10−0.11 WZ

events were expected to have been detected if productionis solely through SM processes.

9

E. Limits on Anomalous WWγ and WWZ Couplings

Since no excess of events in the high-pT (W ) regionwas observed, significant deviations from the SM trilin-ear gauge couplings were excluded. Using the detectionefficiencies for SM WW and WZ production and thebackground subtracted data, upper limits were set onthe anomalous coupling parameters λ and ∆κ. This de-termination was made using a binned likelihood fit ofthe observed pT (W ) spectrum to the prediction of theMonte Carlo signal plus the estimated background. Un-equal width bins were used to evenly distribute the ob-served events, especially those in the high pT (W ) region.In each pT bin for a given set of anomalous coupling pa-rameters, the probability for the sum of the backgroundestimate and Monte Carlo WW/WZ prediction to fluctu-ate to the observed number of events was calculated. Theuncertainties in the background estimations, efficiencies,integrated luminosity, and Monte Carlo signal modellingwere convoluted into the likelihood function using Gaus-sian distributions.

The one-dimensional 95% C.L. limits on λ and ∆κ aresummarized in Table V for Λ = 1.5 TeV and 2.0 TeV.The first two rows provide the coupling limits in the caseof equal couplings for WWZ and WWγ. The last tworows provide limits in the case of HISZ relations [5]. Ineach case, one of the couplings was fixed to its SM valuewhile the other was varied. The two-dimensional bounds(corresponding to a logarithm of the likelihood functionvalue 3.00 below the maximum value) for anomalous cou-pling parameters in the λ−∆κ plane are shown in Fig. 9for Λ = 1.5 TeV. Figure 9 also shows the bounds imposedby the unitary conditions as a larger ellipse.

VI. COMBINED RESULTS

The results of the two searches described in this paperhave been combined with those of our previous publi-cations using the procedure described in Ref. [12]. Themethod was to perform a binned maximum likelihood fitof the number of events and their kinematic characteris-tics to the expected signals and backgrounds, taking careto account for correlated uncertainties among the datasets. The number of events and the expected backgroundin the WZ → trileptons analysis of Section IV, and thepT (µν) spectrum as well as the expected background inthe WW/WZ analysis of Section V, were included intothe multiple final state fit described in Ref. [13]. The re-sulting limits on anomalous couplings represent the mostrestrictive available from our experiment.

Sets of limits were produced using the range of as-sumptions about the relations between the couplings asdiscussed in Section I. Table VI contains limits on λ,∆κ, and where applicable on ∆gZ

1 , for Λ = 1.5 and 2.0

TeV under each of the following assumptions: that theWWγ couplings were equal to the WWZ couplings; thatthe WWγ couplings were related to the WWZ couplingsthrough the HISZ equations (with the additional con-straint αBφ = αWφ); that the WWγ couplings were atthe SM values (producing limits on the WWZ couplings);and that the WWZ couplings were at the SM values (pro-ducing limits on the WWγ couplings). Figure 10 showsthe two-dimensional limit contours and one-dimensionallimit points for λ vs. ∆κ for these four relationships be-tween the WWγ and WWZ couplings. Table VII con-tains limits on αBφ, αWφ, αW , and ∆gZ

1 for Λ = 1.5 and2.0 TeV. Figure 11 shows the two-dimensional limit con-tours and one-dimensional limit points for αW vs. αBφ

when αWφ = 0 and for αW vs. αWφ when αBφ = 0.Note that the Fig. 11(a) limits on αW vs. αBφ are equiv-alent to limits on λγ vs. ∆κγ because ∆gZ

1 is fixed tozero. Also, for purposes of comparison with LEP experi-ments, the central values and 68% C.L. limits on λγ and∆κγ were calculated under the HISZ relations (withoutthe extra constraint αBφ = αWφ) for Λ = 2.0 TeV. Theywere λγ = 0.00+0.10

−0.09 and ∆κγ = −0.08+0.34−0.34.

VII. CONCLUSIONS

Using pp collisions at center-of-mass energy√

s = 1.8TeV detected with the DØ detector, two gauge boson pairproduction processes were studied and used to producelimits on anomalous trilinear gauge boson couplings.

A search for WZ → eνee and µνee candidates yieldedone candidate event where the expected signal from SMWZ production was 0.25± 0.02 events and the expectedbackground was 0.50± 0.17 events. The 95% C.L. upperlimit on the cross section was 47 pb, consistent with, butrather larger than the expected SM cross section. Basedon the one observed event, the detection efficiency, andthe expected background, limits on anomalous WWZcouplings were produced. The one-dimensional limits,at 95% C.L., are |∆gZ

1 | ≤ 1.63 (λZ = 0) and |λ| ≤1.42 (∆gZ

1 = 0) for Λ = 1.0 TeV.A search for anomalous WW/WZ → µνjj production

was performed. The expected background of 224 ± 56events was much larger than the expected SM WW andWZ signal of 4.5±0.8 events. From the pT (µν) distribu-tion of the 224 observed events, which had no significantdeviation from the expected background plus SM signal,limits on anomalous WWγ and WWZ couplings wereproduced. Under the assumption that the WWγ cou-plings equal the WWZ couplings, the one-dimensional95% C.L. limits were −0.43 ≤ λ ≤ 0.44 (∆κ = 0)and −0.60 ≤ ∆κ ≤ 0.74 (λ = 0) for Λ = 2.0 TeV.Under the assumption that the WWγ couplings are re-lated to the WWZ couplings via the HISZ equations,the one-dimensional 95% C.L. limits were −0.42 ≤ λ ≤

10

0.44 (∆κ = 0) and −0.71 ≤ ∆κ ≤ 0.96 (λ = 0) forΛ = 2.0 TeV.

The results of the two searches described in this paperhave been combined with those from our previous publi-cations to produce our most restrictive limits on anoma-lous WWγ and WWZ couplings. Under the assump-tion that the WWγ couplings equal the WWZ couplings,the one-dimensional 95% C.L. limits were −0.18 ≤ λ ≤0.19 (∆κ = 0) and −0.25 ≤ ∆κ ≤ 0.39 (λ = 0) forΛ = 2.0 TeV. Under the assumption that the WWγcouplings are related to the WWZ couplings via theHISZ equations, the one-dimensional 95% C.L. limitswere −0.18 ≤ λ ≤ 0.19 (∆κ = 0) and −0.29 ≤ ∆κ ≤0.53 (λ = 0) for Λ = 2.0 TeV. Limits on ∆κ, λ, and∆gZ

1 were determined for the WWγ couplings assumingthe WWZ couplings are at the SM value, and for theWWZ couplings assuming that the WWγ couplings areat the SM value. Finally, limits on the αBφ, αWφ, andαW anomalous couplings were produced.

We thank the Fermilab and collaborating institutionstaffs for contributions to this work and acknowledgesupport from the Department of Energy and NationalScience Foundation (USA), Commissariat a L’EnergieAtomique (France), Ministry for Science and Technol-ogy and Ministry for Atomic Energy (Russia), CAPESand CNPq (Brazil), Departments of Atomic Energy andScience and Education (India), Colciencias (Colombia),CONACyT (Mexico), Ministry of Education and KOSEF(Korea), and CONICET and UBACyT (Argentina).

VIII. APPENDIX: PARAMETERS OF THE WZCANDIDATE EVENT

Given the expected signal to background ratio of ap-proximately one to two in the channel WZ → eνee, thereis no certainty that the candidate event is actually dueto WZ production. But due to the event’s striking sig-nature it is described in detail in this appendix.

The candidate event contains three high-ET electroncandidates and large missing transverse energy (46.2GeV). The event contains no other high-pT objects (jetsor muons). The properties of the candidate electrons aresummarized in Table VIII. The missing transverse en-ergy and the various mass combinations of the electronswith the missing transverse energy are listed in Table IX.The invariant mass of electron candidates 1 and 3 is 93.6GeV/c2, and the transverse mass formed using electroncandidate 2 and the missing transverse energy is 74.7GeV/c2.

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[24] DELPHI Collaboration, P. Abreu et al., Phys. Lett. B397, 158 (1997).

[25] DELPHI Collaboration, P. Abreu et al., Phys. Lett. B423, 194 (1998).

[26] ALEPH Collaboration, R. Barate et al., Phys. Lett. B422, 369 (1998).

[27] DØ Collaboration, S. Abachi et al., Nucl. Instrum. Meth-ods Phys. Res. A 338, 185 (1994).

[28] Pseudorapidity, η, is defined as − ln tan θ/2 where θ is thepolar angle. In the definition of the pseudorapidity of thecalorimeter detector boundaries, the origin was the centerof the calorimeter. In the definition of the pseudorapidityof an object such as an electron or muon, the origin was

11

the pp collision point.[29] J. Bantly et al., Fermilab TM-1995 (1997).[30] P. E. Gartung, Ph. D. thesis, University of Cali-

fornia at Riverside, 1998 (unpublished), http://www-d0.fnal.gov/publications talks/thesis/gartung/thesis.ps.

[31] A. D. Martin, R. G. Roberts, and W. J. Stirling, Phys.Rev. D 47, 867 (1993).

[32] T. Sjostrand, “PYTHIA 5.6 and Jetset 7.3 Physics andManual”, CERN-TH.6488/92, 1992 (unpublished).

[33] J. Ohnemus, Phys. Rev. D 44, 3477 (1991).[34] Particle Data Group, R. M. Barnett et al., Phys. Rev. D

54, 1 (1996).[35] U. Baur, private communication. The unitarity limit con-

tour was the ellipse where

Λ =

4.33

λ2Z +

M2W

2M2Z

∆gZ1

1

4

with Λ given in TeV.[36] DØ Collaboration, B. Abbott et al., Phys. Rev. D 58,

052001 (1998).[37] F. A. Berends et al., Nucl. Phys. B357, 32 (1991).[38] G. Marchesini et al., Comput. Phys. Commun. 67, 465

(1992).[39] F. Carminati et al., GEANT Users Guide, CERN Pro-

gram Library Long Writeup WS013 (1993), unpublished.[40] DØ Collaboration, S. Abachi et al., Phys. Rev. Lett. 79,

1203 (1997).

12

Electron Type Efficiency (CC) % Efficiency (EC) %

Loose 88.6 ± 0.3 88.4 ± 0.5

Tight 73.4 ± 0.5 67.2 ± 0.3

TABLE I. Measured efficiencies for electron identificationin the CC and two EC’s. See text for definitions of tight andloose.

Electron CC ECType a0 × 103 a1 × 105 a0 × 103 a1 × 105

Loose 0.08 ± 0.29 2.06 ± 0.70 1.3 ± 1.0 6.31 ± 0.27

Tight −0.17 ± 0.20 1.43 ± 0.51 0.53 ± 0.86 5.1 ± 2.3

TABLE II. Jet misidentification probabilities for tight andloose electrons. The probability is a linear function ofET (GeV), a0 + a1 × ET (GeV). Uncertainties given in thistable are statistical only. A systematic uncertainty of 25%was assigned to each fake probability.

eνee µνee Total

L 92.3 ± 5.0 pb−1

ǫ 0.169 ± 0.014 0.115 ± 0.014Br 0.36% ± 0.01%

Nobs 1 0 1Nbkg 0.38 ± 0.14 0.12 ± 0.04 0.50 ± 0.17NSM 0.15 ± 0.01 0.10 ± 0.01 0.25 ± 0.02

TABLE III. Summary of the WZ → lνll results. L is theintegrated luminosity, ǫ is the overall detection efficiency, Bris the branching ratio, Nobs is the number of events observed,Nbkg is the number of background events, and NSM is thepredicted number of SM events.

Sample Number of Events

QCD multi-jet background 105±19 (stat)

W + > 2 jets background 117±24 (stat)

tt background 2.7±1.2 (stat)

Total background 224±31 (stat) ±46 (syst)

SM prediction 4.5±0.8 (stat + syst)

Observed data sample(luminosity = 80.7 pb−1) 224

TABLE IV. Comparison of signal (data) and backgroundsfor the mode WW/WZ → µνjj. The data sample is consistentwith the SM prediction and estimated backgrounds showingno evidence for anomalous gauge couplings.

Coupling Λ = 1.5 TeV Λ = 2.0 TeV

λγ = λZ −0.45, 0.46 −0.43, 0.44

∆κγ = ∆κZ −0.62, 0.78 −0.60, 0.74

λγ = λZ(HISZ) −0.44, 0.46 −0.42, 0.44

∆κγ(HISZ) −0.75, 0.99 −0.71, 0.96

TABLE V. Axis limits (one-dimensional) at the 95% C.L.with two assumptions for the relation between the WWγ andWWZ couplings (WWγ = WWZ and HISZ) and for twodifferent values of Λ in the mode WW/WZ → µνjj.

Coupling Λ = 1.5 TeV Λ = 2.0 TeV

λγ = λZ (∆κγ = ∆κZ = 0) −0.20, 0.20 −0.18, 0.19∆κγ = ∆κZ (λγ = λZ = 0) −0.27, 0.42 −0.25, 0.39

λγ(HISZ) (∆κγ = 0) −0.20, 0.20 −0.18, 0.19∆κγ(HISZ) (λγ = 0) −0.31, 0.56 −0.29, 0.53

λZ(SM WWγ) (∆κZ = ∆gZ1 = 0) −0.26, 0.29 −0.24, 0.27

∆κZ(SM WWγ) (λZ = ∆gZ1 = 0) −0.37, 0.55 −0.34, 0.51

∆gZ1 (SM WWγ) (λZ = ∆κZ = 0) −0.39, 0.62 −0.37, 0.57

λγ(SM WWZ) (∆κγ = 0) −0.27, 0.25 −0.25, 0.24∆κγ(SM WWZ) (λγ = 0) −0.57, 0.74 −0.54, 0.69

TABLE VI. One-dimensional limits at 95% C.L. froma simultaneous fit to the DØ Wγ, WW → dilepton,WW/WZ → eνjj, WW/WZ → µνjj, and WZ → trilep-ton data samples. The HISZ results included the additionalconstraint αBφ = αWφ.

Coupling Λ = 1.5 TeV Λ = 2.0 TeV

αBφ (αWφ = αW = 0) −0.73, 0.59 −0.67, 0.56

αWφ (αBφ = αW = 0) −0.19, 0.38 −0.18, 0.36

αW (αBφ = αWφ = 0) −0.20, 0.20 −0.18, 0.19

∆gZ1 (αBφ = αW = 0) −0.25, 0.49 −0.23, 0.47

TABLE VII. One-dimensional limits at 95% C.L. on α pa-rameters from a simultaneous fit to the DØ Wγ, WW →dilepton, WW/WZ → eνjj, WW/WZ → µνjj, and WZ →trilepton data samples.

e1 e2 e3

ET (GeV) 54.5 50.9 37.7η 0.11 −0.62 1.37φ 5.94 3.04 4.14

TABLE VIII. Kinematic properties of the WZ → eνeecandidate event (Run 89912, Event 23020).

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Mass Combination Information

Me1,e2= 111.8 GeV/c2 Me1,e2,e3

= 171.7 GeV/c2

Me1,e3= 93.6 GeV/c2 Me2,e3

= 112.4 GeV/c2

/ET = 46.2 GeV φ( /ET ) = 1.29MT (ei, /ET ) = 73.0, 74.7, 82.6 GeV/c2 for e1, e2, e3 respectivelypT (e1, e3) = 58.8 GeV/c φ(e1, e3) = −1.02pT (e2, /ET ) = 63.0 GeV/c φ(e2, /ET ) = 2.22

TABLE IX. Mass combination information for eνee can-didate event. Mei,ej

is the invariant mass of electron i andelectron j. Me1,e2,e3

is the three-body mass of electron 1,electron 2, and electron 3. MT is the transverse mass and pT

is the transverse momentum.

Muon Toroids

Calorimeters

Central Tracking

System and PDT’s

xz

y

FIG. 1. Isometric view of the DØ detector. Also shownare the calorimeter support platform, the Tevatron beampipecentered within the calorimeter, and the Main Ring beampipewhich penetrated the muon system and calorimeter above thedetector center.

0 1 2 3 4 5 6

-1-0.5

00.51

0

0.2

0.4

0.6

η

φ (rad)

FIG. 2. The geometrical acceptance of the muon detectorwithin the region |η| ≤ 1. φ = 3π

2is the downward (−y)

direction where the calorimeter support platform breaks intothe muon system three-layer geometry.

14

02.5

57.510

250 500 750 1000 1250 1500 1750 2000

λ Z

0

10

20

30

250 500 750 1000 1250 1500 1750 2000

∆κZ

0

2

4

6

250 500 750 1000 1250 1500 1750 2000ΛFF(GeV)

∆g1Z

FIG. 3. One-dimensional 95% C.L. (solid) and unitaritylimits (dashed) vs. Λ for the WWZ coupling parameters λZ ,∆κZ , and ∆gZ

1 .

-3

-2

-1

0

1

2

3

-3 -2 -1 0 1 2 3∆g1

Z

λ Z

Unitarity LimitsΛFF = 1 TeV

2-D 95% CL

FIG. 4. Correlated limits on ∆gZ1 and λZ for Λ = 1 TeV

obtained from a fit to the cross section using the 1994–1996data for the µνee and eνee channels combined. The innersolid line is the two-dimensional 95% C.L. limit and the outersolid line is the unitarity limit.

FIG. 5. Jet trigger efficiency in pseudorapidity region|η| < 1.0. The curve is the result of an error function fitto the efficiency.

FIG. 6. Comparison of invariant mass of the two highestET jets for the data (histogram) and the estimated total back-ground (points with uncertainties) for the WW/WZ → µνjjchannel. The uncertainties shown are statistical only.

15

FIG. 7. Comparison of the pT (W ) distributions of signal(histogram) and estimated total background (× with statis-tical uncertainties) for WW/WZ → µνjj. They are consis-tent with each other indicating the presence of no significantanomalous gauge couplings.

FIG. 8. The efficiency of the dijet reconstruction and selec-tion as a function of pT (µν) in the WW/WZ → µνjj analysis.The uncertainties shown are statistical only.

-2

-1

0

1

2

-2 -1 0 1 2

FIG. 9. Contour plot of allowed region in the λ−∆κ spacefor WW/WZ → µνjj at 95% C.L. for Λ = 1.5 TeV. The outerellipse shows the bounds imposed by the unitary relations onλ and ∆κ.

16

-1

0

1

-1 0 1∆κ

λ(a) equal couplings

-1

0

1

-1 0 1∆κγ

λ γ

(b) HISZ

-1

0

1

-1 0 1∆κZ

λ Z

(c) SM WWγ

U(1)

-1

0

1

-1 0 1∆κγ

λ γ(d) SM WWZ

FIG. 10. Contour limits on anomalous couplings froma simultaneous fit to the DØ Wγ, WW → dilep-ton, WW/WZ → eνjj, WW/WZ → µνjj, andWZ → trilepton final states for Λ = 1.5 TeV: (a)∆κ ≡ ∆κγ = ∆κZ , λ ≡ λγ = λZ ; (b) HISZ relations; (c)SM WWγ couplings; and (d) SM WWZ couplings. (a), (c),and (d) assume that ∆gZ

1 = 0. The solid circles correspondto 95% C.L. one-degree of freedom exclusion limits. The in-ner and outer curves are the 95% C.L. two-degree of freedomexclusion contour and the constraint from the unitarity con-dition, respectively. In (d), the unitarity contour is locatedoutside of the boundary of the plot. The HISZ results includethe additional constraint αBφ = αWφ.

-1

0

1

-1 0 1αBφ

α W

(a)

-1

0

1

-1 0 1αWφ

α W

(b)

FIG. 11. Contour limits on anomalous couplings froma simultaneous fit to the DØ Wγ, WW → dilepton,WW/WZ → eνjj, WW/WZ → µνjj, and WZ → trileptonfinal states for Λ = 1.5 TeV: (a) αW vs. αBφ when αWφ = 0;and (b) αW vs. αWφ when αBφ = 0. The solid circles cor-respond to 95% C.L. one-degree of freedom exclusion limits.The inner and outer curves are the 95% C.L. two-degree offreedom exclusion contour and the constraint from the uni-tarity condition, respectively.

17