Article
Reference
Search for ZZ and ZW production in pp collisions at s√=1.96 TeV
CDF Collaboration
CAMPANELLI, Mario (Collab.), et al.
Abstract
We present a search for ZZ and ZW vector boson pair production in pp¯ collisions at s√=1.96 TeV using the leptonic decay channels ZZ→llνν, ZZ→lll′l′, and ZW→lll′ν. In a data sample corresponding to an integrated luminosity of 194 pb−1 collected with the Collider Detector at Fermilab, 3 candidate events are found with an expected background of 1.0±0.2 events. We set a 95% confidence level upper limit of 15.2 pb on the cross section for ZZ plus ZW production, compared to the standard model prediction of 5.0±0.4 pb.
CDF Collaboration, CAMPANELLI, Mario (Collab.), et al . Search for ZZ and ZW production in pp collisions at s√=1.96 TeV. Physical Review. D , 2005, vol. 71, no. 09, p. 091105
DOI : 10.1103/PhysRevD.71.091105
Available at:
http://archive-ouverte.unige.ch/unige:38300
Disclaimer: layout of this document may differ from the published version.
1 / 1
Search for ZZ and ZW production in p p collisions at p s
1:96 TeV
D. Acosta,16J. Adelman,12T. Affolder,9T. Akimoto,54M. G. Albrow,15D. Ambrose,43S. Amerio,42D. Amidei,33 A. Anastassov,50K. Anikeev,15A. Annovi,44J. Antos,1M. Aoki,54G. Apollinari,15T. Arisawa,56J-F. Arguin,32 A. Artikov,13W. Ashmanskas,15A. Attal,7F. Azfar,41P. Azzi-Bacchetta,42N. Bacchetta,42H. Bachacou,28W. Badgett,15 A. Barbaro-Galtieri,28G. J. Barker,25V. E. Barnes,46B. A. Barnett,24S. Baroiant,6M. Barone,17G. Bauer,31F. Bedeschi,44
S. Behari,24S. Belforte,53G. Bellettini,44J. Bellinger,58E. Ben-Haim,15D. Benjamin,14A. Beretvas,15A. Bhatti,48 M. Binkley,15D. Bisello,42M. Bishai,15R. E. Blair,2C. Blocker,5K. Bloom,33B. Blumenfeld,24A. Bocci,48A. Bodek,47
G. Bolla,46A. Bolshov,31P. S. L. Booth,29D. Bortoletto,46J. Boudreau,45S. Bourov,15B. Brau,9C. Bromberg,34 E. Brubaker,12J. Budagov,13H. S. Budd,47K. Burkett,15G. Busetto,42P. Bussey,19K. L. Byrum,2S. Cabrera,14 M. Campanelli,18M. Campbell,33A. Canepa,46M. Casarsa,53D. Carlsmith,58S. Carron,14R. Carosi,44M. Cavalli-Sforza,3
A. Castro,4P. Catastini,44D. Cauz,53A. Cerri,28L. Cerrito,23J. Chapman,33C. Chen,43Y. C. Chen,1M. Chertok,6 G. Chiarelli,44G. Chlachidze,13F. Chlebana,15I. Cho,27K. Cho,27D. Chokheli,13J. P. Chou,20M. L. Chu,1S. Chuang,58
J. Y. Chung,38W-H. Chung,58Y. S. Chung,47C. I. Ciobanu,23M. A. Ciocci,44A. G. Clark,18D. Clark,5M. Coca,47 A. Connolly,28M. Convery,48J. Conway,6B. Cooper,30M. Cordelli,17G. Cortiana,42J. Cranshaw,52J. Cuevas,10 R. Culbertson,15C. Currat,28D. Cyr,58D. Dagenhart,5S. Da Ronco,42S. D’Auria,19P. de Barbaro,47S. De Cecco,49
G. De Lentdecker,47S. Dell’Agnello,17M. Dell’Orso,44S. Demers,47L. Demortier,48J. Deng,14M. Deninno,4 D. De Pedis,49P. F. Derwent,15C. Dionisi,49J. R. Dittmann,15C. Do¨rr,25P. Doksus,23A. Dominguez,28S. Donati,44 M. Donega,18J. Donini,42M. D’Onofrio,18T. Dorigo,42V. Drollinger,36K. Ebina,56N. Eddy,23J. Ehlers,18R. Ely,28
R. Erbacher,6M. Erdmann,25D. Errede,23S. Errede,23R. Eusebi,47H-C. Fang,28S. Farrington,29I. Fedorko,44 W. T. Fedorko,12R. G. Feild,59M. Feindt,25J. P. Fernandez,46C. Ferretti,33R. D. Field,16G. Flanagan,34B. Flaugher,15
L. R. Flores-Castillo,45A. Foland,20S. Forrester,6G. W. Foster,15M. Franklin,20J. C. Freeman,28Y. Fujii,26I. Furic,12 A. Gajjar,29A. Gallas,37J. Galyardt,11M. Gallinaro,48M. Garcia-Sciveres,28A. F. Garfinkel,46C. Gay,59H. Gerberich,14
D. W. Gerdes,33E. Gerchtein,11S. Giagu,49P. Giannetti,44A. Gibson,28K. Gibson,11C. Ginsburg,58K. Giolo,46 M. Giordani,53M. Giunta,44G. Giurgiu,11V. Glagolev,13D. Glenzinski,15M. Gold,36N. Goldschmidt,33D. Goldstein,7
J. Goldstein,41G. Gomez,10G. Gomez-Ceballos,10M. Goncharov,51O. Gonza´lez,46I. Gorelov,36A. T. Goshaw,14 Y. Gotra,45K. Goulianos,48A. Gresele,4M. Griffiths,29C. Grosso-Pilcher,12U. Grundler,23M. Guenther,46 J. Guimaraes da Costa,20C. Haber,28K. Hahn,43S. R. Hahn,15E. Halkiadakis,47A. Hamilton,32B-Y. Han,47R. Handler,58 F. Happacher,17K. Hara,54M. Hare,55R. F. Harr,57R. M. Harris,15F. Hartmann,25K. Hatakeyama,48J. Hauser,7C. Hays,14 H. Hayward,29E. Heider,55B. Heinemann,29J. Heinrich,43M. Hennecke,25M. Herndon,24C. Hill,9D. Hirschbuehl,25 A. Hocker,47K. D. Hoffman,12A. Holloway,20S. Hou,1M. A. Houlden,29B. T. Huffman,41Y. Huang,14R. E. Hughes,38
J. Huston,34K. Ikado,56J. Incandela,9G. Introzzi,44M. Iori,49Y. Ishizawa,54C. Issever,9A. Ivanov,47Y. Iwata,22 B. Iyutin,31E. James,15D. Jang,50J. Jarrell,36D. Jeans,49H. Jensen,15E. J. Jeon,27M. Jones,46K. K. Joo,27S. Y. Jun,11 T. Junk,23T. Kamon,51J. Kang,33M. Karagoz Unel,37P. E. Karchin,57S. Kartal,15Y. Kato,40Y. Kemp,25R. Kephart,15
U. Kerzel,25V. Khotilovich,51B. Kilminster,38D. H. Kim,27H. S. Kim,23J. E. Kim,27M. J. Kim,11M. S. Kim,27 S. B. Kim,27S. H. Kim,54T. H. Kim,31Y. K. Kim,12B. T. King,29M. Kirby,14L. Kirsch,5S. Klimenko,16B. Knuteson,31 B. R. Ko,14H. Kobayashi,54P. Koehn,38D. J. Kong,27K. Kondo,56J. Konigsberg,16K. Kordas,32A. Korn,31A. Korytov,16
K. Kotelnikov,35A. V. Kotwal,14A. Kovalev,43J. Kraus,23I. Kravchenko,31A. Kreymer,15J. Kroll,43M. Kruse,14 V. Krutelyov,15S. E. Kuhlmann,2S. Kwang,12A. T. Laasanen,46S. Lai,32S. Lami,48S. Lammel,15J. Lancaster,14 M. Lancaster,30R. Lander,6K. Lannon,38A. Lath,50G. Latino,36R. Lauhakangas,21I. Lazzizzera,42Y. Le,24C. Lecci,25 T. LeCompte,2J. Lee,27J. Lee,47S. W. Lee,51R. Lefe`vre,3N. Leonardo,31S. Leone,44S. Levy,12J. D. Lewis,15K. Li,59 C. Lin,59C. S. Lin,15M. Lindgren,15T. M. Liss,23A. Lister,18D. O. Litvintsev,15T. Liu,15Y. Liu,18N. S. Lockyer,43 A. Loginov,35M. Loreti,42P. Loverre,49R-S. Lu,1D. Lucchesi,42P. Lujan,28P. Lukens,15G. Lungu,16L. Lyons,41J. Lys,28 R. Lysak,1D. MacQueen,32R. Madrak,15K. Maeshima,15P. Maksimovic,24L. Malferrari,4G. Manca,29R. Marginean,38
C. Marino,23A. Martin,24M. Martin,59V. Martin,37M. Martı´nez,3T. Maruyama,54H. Matsunaga,54M. Mattson,57 P. Mazzanti,4K. S. McFarland,47D. McGivern,30P. M. McIntyre,51P. McNamara,50R. NcNulty,29A. Mehta,29 S. Menzemer,31A. Menzione,44P. Merkel,15C. Mesropian,48A. Messina,49T. Miao,15N. Miladinovic,5L. Miller,20 R. Miller,34J. S. Miller,33R. Miquel,28S. Miscetti,17G. Mitselmakher,16A. Miyamoto,26Y. Miyazaki,40N. Moggi,4
B. Mohr,7R. Moore,15M. Morello,44P. A. Movilla Fernandez,28A. Mukherjee,15M. Mulhearn,31T. Muller,25 R. Mumford,24A. Munar,43P. Murat,15J. Nachtman,15S. Nahn,59I. Nakamura,43I. Nakano,39A. Napier,55R. Napora,24
D. Naumov,36V. Necula,16F. Niell,33J. Nielsen,28C. Nelson,15T. Nelson,15C. Neu,43M. S. Neubauer,8
C. Newman-Holmes,15T. Nigmanov,45L. Nodulman,2O. Norniella,3K. Oesterberg,21T. Ogawa,56S. H. Oh,14Y. D. Oh,27 T. Ohsugi,22T. Okusawa,40R. Oldeman,49R. Orava,21W. Orejudos,28C. Pagliarone,44E. Palencia,10R. Paoletti,44 V. Papadimitriou,15S. Pashapour,32J. Patrick,15G. Pauletta,53M. Paulini,11T. Pauly,41C. Paus,31D. Pellett,6A. Penzo,53 T. J. Phillips,14G. Piacentino,44J. Piedra,10K. T. Pitts,23C. Plager,7A. Pomposˇ,46L. Pondrom,58G. Pope,45X. Portell,3
O. Poukhov,13F. Prakoshyn,13T. Pratt,29A. Pronko,16J. Proudfoot,2F. Ptohos,17G. Punzi,44J. Rademacker,41 M. A. Rahaman,45A. Rakitine,31S. Rappoccio,20F. Ratnikov,50H. Ray,33B. Reisert,15V. Rekovic,36P. Renton,41
M. Rescigno,49F. Rimondi,4K. Rinnert,25L. Ristori,44W. J. Robertson,14A. Robson,41T. Rodrigo,10S. Rolli,55 L. Rosenson,31R. Roser,15R. Rossin,42C. Rott,46J. Russ,11V. Rusu,12A. Ruiz,10D. Ryan,55H. Saarikko,21S. Sabik,32
A. Safonov,6R. St. Denis,19W. K. Sakumoto,47G. Salamanna,49D. Saltzberg,7C. Sanchez,3A. Sansoni,17L. Santi,53 S. Sarkar,49K. Sato,54P. Savard,32A. Savoy-Navarro,15P. Schlabach,15E. E. Schmidt,15M. P. Schmidt,59M. Schmitt,37
L. Scodellaro,10A. Scribano,44F. Scuri,44A. Sedov,46S. Seidel,36Y. Seiya,40F. Semeria,4L. Sexton-Kennedy,15 I. Sfiligoi,17M. D. Shapiro,28T. Shears,29P. F. Shepard,45D. Sherman,20M. Shimojima,54M. Shochet,12Y. Shon,58 I. Shreyber,35A. Sidoti,44J. Siegrist,28M. Siket,1A. Sill,52P. Sinervo,32A. Sisakyan,13A. Skiba,25A. J. Slaughter,15
K. Sliwa,55D. Smirnov,36J. R. Smith,6F. D. Snider,15R. Snihur,32A. Soha,6S. V. Somalwar,50J. Spalding,15 M. Spezziga,52L. Spiegel,15F. Spinella,44M. Spiropulu,9P. Squillacioti,44H. Stadie,25B. Stelzer,32O. Stelzer-Chilton,32 J. Strologas,36D. Stuart,9A. Sukhanov,16K. Sumorok,31H. Sun,55T. Suzuki,54A. Taffard,23R. Tafirout,32S. F. Takach,57 H. Takano,54R. Takashima,22Y. Takeuchi,54K. Takikawa,54M. Tanaka,2R. Tanaka,39N. Tanimoto,39S. Tapprogge,21
M. Tecchio,33P. K. Teng,1K. Terashi,48R. J. Tesarek,15S. Tether,31J. Thom,15A. S. Thompson,19E. Thomson,43 P. Tipton,47V. Tiwari,11S. Tkaczyk,15D. Toback,51K. Tollefson,34T. Tomura,54D. Tonelli,44M. To¨nnesmann,34 S. Torre,44D. Torretta,15S. Tourneur,15W. Trischuk,32J. Tseng,41R. Tsuchiya,56S. Tsuno,39D. Tsybychev,16N. Turini,44
M. Turner,29F. Ukegawa,54T. Unverhau,19S. Uozumi,54D. Usynin,43L. Vacavant,28A. Vaiciulis,47A. Varganov,33 E. Vataga,44S. Vejcik III,15G. Velev,15V. Veszpremi,46G. Veramendi,23T. Vickey,23R. Vidal,15I. Vila,10R. Vilar,10 I. Vollrath,32I. Volobouev,28M. von der Mey,7P. Wagner,51R. G. Wagner,2R. L. Wagner,15W. Wagner,25R. Wallny,7
T. Walter,25T. Yamashita,39K. Yamamoto,40Z. Wan,50M. J. Wang,1S. M. Wang,16A. Warburton,32B. Ward,19 S. Waschke,19D. Waters,30T. Watts,50M. Weber,28W. C. Wester III,15B. Whitehouse,55A. B. Wicklund,2E. Wicklund,15
H. H. Williams,43P. Wilson,15B. L. Winer,38P. Wittich,43S. Wolbers,15C. Wolfe,12M. Wolter,55M. Worcester,7 S. Worm,50T. Wright,33X. Wu,18F. Wu¨rthwein,8A. Wyatt,30A. Yagil,15C. Yang,59U. K. Yang,12W. Yao,28G. P. Yeh,15 K. Yi,24J. Yoh,15P. Yoon,47K. Yorita,56T. Yoshida,40I. Yu,27S. Yu,43Z. Yu,59J. C. Yun,15L. Zanello,49A. Zanetti,53
I. Zaw,20F. Zetti,44J. Zhou,50A. Zsenei,18and S. Zucchelli4
1Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China
2Argonne National Laboratory, Argonne, Illinois 60439, USA
3Institut de Fisica d’Altes Energies, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain
4Istituto Nazionale di Fisica Nucleare, University of Bologna, I-40127 Bologna, Italy
5Brandeis University, Waltham, Massachusetts 02254, USA
6University of California at Davis, Davis, California 95616, USA
7University of California at Los Angeles, Los Angeles, California 90024, USA
8University of California at San Diego, La Jolla, California 92093, USA
9University of California at Santa Barbara, Santa Barbara, California 93106, USA
10Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain
11Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
12Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA
13Joint Institute for Nuclear Research, RU-141980 Dubna, Russia
14Duke University, Durham, North Carolina 27708, USA
15Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
16University of Florida, Gainesville, Florida 32611, USA
17Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy
18University of Geneva, CH-1211 Geneva 4, Switzerland
19Glasgow University, Glasgow G12 8QQ, United Kingdom
20Harvard University, Cambridge, Massachusetts 02138, USA
21The Helsinki Group: Helsinki Institute of Physics; and Division of High Energy Physics, Department of Physical Sciences, University of Helsinki, FIN-00044, Helsinki, Finland
22Hiroshima University, Higashi-Hiroshima 724, Japan
23University of Illinois, Urbana, Illinois 61801, USA
24The Johns Hopkins University, Baltimore, Maryland 21218, USA
25Institut fu¨r Experimentelle Kernphysik, Universita¨t Karlsruhe, 76128 Karlsruhe, Germany
D. ACOSTAet al. PHYSICAL REVIEW D71,091105 (2005)
091105-2
26High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305, Japan
27Center for High Energy Physics: Kyungpook National University, Taegu 702-701, Korea;
Seoul National University, Seoul 151-742, Korea; and SungKyunKwan University, Suwon 440-746, Korea
28Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
29University of Liverpool, Liverpool L69 7ZE, United Kingdom
30University College London, London WC1E 6BT, United Kingdom
31Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
32Institute of Particle Physics: McGill University, Montre´al, Canada H3A 2T8; and University of Toronto, Toronto, Canada M5S 1A7
33University of Michigan, Ann Arbor, Michigan 48109, USA
34Michigan State University, East Lansing, Michigan 48824, USA
35Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia
36University of New Mexico, Albuquerque, New Mexico 87131, USA
37Northwestern University, Evanston, Illinois 60208, USA
38The Ohio State University, Columbus, Ohio 43210, USA
39Okayama University, Okayama 700-8530, Japan
40Osaka City University, Osaka 588, Japan
41University of Oxford, Oxford OX1 3RH, United Kingdom
42University of Padova, Istituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova, Italy
43University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
44Istituto Nazionale di Fisica Nucleare, University and Scuola Normale Superiore of Pisa, I-56100 Pisa, Italy
45University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
46Purdue University, West Lafayette, Indiana 47907, USA
47University of Rochester, Rochester, New York 14627, USA
48The Rockefeller University, New York, New York 10021, USA
49Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1, University di Roma La Sapienza, I-00185 Roma, Italy
50Rutgers University, Piscataway, New Jersey 08855, USA
51Texas A&M University, College Station, Texas 77843, USA
52Texas Tech University, Lubbock, Texas 79409, USA
53Istituto Nazionale di Fisica Nucleare, University of Trieste/Udine, Italy
54University of Tsukuba, Tsukuba, Ibaraki 305, Japan
55Tufts University, Medford, Massachusetts 02155, USA
56Waseda University, Tokyo 169, Japan
57Wayne State University, Detroit, Michigan 48201, USA
58University of Wisconsin, Madison, Wisconsin 53706, USA
59Yale University, New Haven, Connecticut 06520, USA (Received 6 January 2005; published 16 May 2005)
We present a search forZZandZWvector boson pair production inpp collisions at ps
1:96 TeV using the leptonic decay channelsZZ!ll,ZZ!lll0l0, andZW!lll0. In a data sample correspond- ing to an integrated luminosity of194 pb1collected with the Collider Detector at Fermilab, 3 candidate events are found with an expected background of1:00:2events. We set a 95% confidence level upper limit of 15.2 pb on the cross section for ZZ plus ZW production, compared to the standard model prediction of5:00:4 pb.
DOI: 10.1103/PhysRevD.71.091105 PACS numbers: 13.85.Rm, 12.15.Ji, 14.70.Fm, 14.70.Hp
The measurements ofZZandZW production provide a direct test of the standard model (SM) prediction of triple- gauge-boson couplings [1]. The presence of unexpected neutral triple-gauge-boson couplings (ZZZandZZ ) can result in an enhanced rate ofZZproduction, and an anoma- lousWWZcoupling can increase the ZW production rate above the SM prediction. The WWZ andZZ couplings have been studied by the CDF and D0 experiments through the study ofWW,ZW,W , andZ production [2 –8]. The D0 experiment has measured an upper limit on the cross section forZWproduction [4]. No limit has been set on the cross section forZZproduction from hadron collisions, but production properties have been studied at LEP II inee
collisions at ps
183209 GeV[9]. A comprehensive review of the limits on anomalous WWZ,ZZZ, andZZ couplings at LEP II can be found in Ref. [10]. The produc- tion ofWZandZZ boson pairs is also of interest because the decays cause significant backgrounds in searches for the SM Higgs boson.
In this report we present a search for ZZ and ZW production using the three decay modesZZ!ll,ZZ! lll0l0, and ZW !lll0, where l and l0 are electrons or muons, predominantly from direct W or Z decays, but also with a small contribution from the leptonic decay of tau leptons. This study is based on19412 pb1[11] of data collected by the upgraded Collider Detector at
Fermilab (CDF II) from March 2002 to September 2003 usingppcollisions at
ps
1:96 TeV. CDF II is a general- purpose detector at the Tevatron accelerator at Fermilab.
The main components used in this analysis are a silicon vertex detector, a central tracking drift chamber, central (jj<1:1 [12]) and forward (1:1<jj<3:6) electro- magnetic and hadronic calorimeters, and muon chambers.
The silicon detector and central tracking chamber are located inside a 1.4 T superconducting solenoidal magnet.
A more detailed description of the detector can be found in the CDF technical design report [13] and in a recent publication describing a measurement ofWWpair produc- tion [8].
The data samples are collected by a trigger system that selects events having electron candidates in the central calorimeter withET>18 GeV, or muon candidates with pT>18 GeV=c. Events for this analysis are then selected by requiring at least two leptons with ET>20 GeV and jj<2:5for electrons, orpT>20 GeV=candjj<1for muons. An electron is identified as energy deposited in the central electromagnetic calorimeter which is matched to a well-measured track reconstructed in the central tracking chamber, or, for an electron with jj>1:2, as energy deposited in the forward electromagnetic calorimeter with an associated track utilizing a calorimeter-seeded silicon tracking algorithm [14]. In addition, electrons must have appropriate shower profiles in the electromag- netic calorimeters. A muon is identified as a track in the central tracking chamber, with energy deposition in the calorimeter consistent with a minimum ionizing particle, and with a track segment in the muon chambers. If a minimum ionizing track points towards a gap in the muon chamber coverage, it is still considered a muon candidate in events that have an additional electron in the central calorimeter or a muon with a muon chamber track segment. All charged leptons are required to be isolated from additional nearby calorimeter activity. The transverse energy deposited around an electron or muon in a cone of
radius R
22
p 0:4, excluding the calo- rimeter energy matched to the lepton candidate, is required to be less then 10% of the electronET or muonpT.
The signature of neutrinos in the decays ofZZ!ll andZW !lll0 is missing transverse energy (6ET), mea- sured from the imbalance ofET in the calorimeter and the escaping muonpT (when muon candidates are present).
The next-to-leading-order (NLO) ZZ and ZW cross sections inpp collisions atps
1:96 TeVare calculated by the MCFM [15] program using the CTEQ6 parton distribution functions [16]. They are pp !ZZ 1:390:10 pbandpp !ZW 3:650:26 pb.
We study events in three categories designed to encom- pass the main leptonic branching ratios of theZZandZW decays. The first includes events with four charged leptons, which is sensitive toZZ!lll0l0(landl0e; ; ) with a branching ratio of 1.0%. Since we only select events with
electrons and/or muons, we are only sensitive to final-state taus through their subsequent decay to leptons. The second category, which includes events with three charged leptons plus6ET, consists predominantly ofZW!lll0(branching ratio of 3.3%). Events fromZZ!lll0l0, where one lepton is not identified, can also fall into this category. The third category includes events with two charged leptons plus6ET, which is sensitive toZZ!ll(branching ratio of 4.0%) andZW!lll0, where one lepton is not identified.
Our strategy is to first select events containing aZboson and then require additional leptons and/or large 6ET in the event. TheZboson is identified by one pair of same-flavor oppositely-charged leptons (ee or ) with an in- variant mass between 76 GeV=c2 and106 GeV=c2. The four-lepton category selects a second lepton pair using the same criteria. The three-lepton plus6ETcategory selects, in addition to theZboson, a third charged lepton withET>
20 GeV (pT>20 GeV=c for muons) and 6ET GeV. For two-lepton events, in order to reduce the significant con- tribution fromWWboson pairs, we selectZbosons using a narrower invariant mass range of 86< Mll<96 GeV=c2. Two additional requirements are designed to suppress the Drell-Yan background in the two-lepton category. The first requires6ET significance (6EsigT ) to be larger than3 GeV1=2, where6EsigT is defined as6ET=pPET
and the sum is over all calorimeter towers above a given threshold. If muons are identified in the event,PETis also corrected for the muon momenta. We find that6EsigT is a better discriminant than6ET in controlling the Drell-Yan background, and that the maximum expected signal significance is achieved when 6EsigT is at least3 GeV1=2. The second requirement is for between 6ET and the closest lepton or jet,(6ET, lepton/
jet), to be larger than 20, in order to reduce the likelihood of falsely-reconstructed large 6ET due to mismeasured jets or leptons. Finally, in the two-lepton category we only consider events with zero or one jet to suppress tt back- ground. In this analysis, jets are reconstructed using a cone of fixed radius R0:4 [17], and are counted if ET>
15 GeVandjj<2:5.
The main background in the four-lepton and three- lepton categories is from ‘‘fake-lepton’’ events, in which jets have been misidentified as leptons in Z=Wjets events. The backgrounds in the two-lepton category in- cludeWW,tt, Drell-Yan, and fake-lepton events.
For each of the three categories of events, the total efficiency for accepting aZZorZWevent can be expressed as totalIDtriggergeom-kin, where ID is the effi- ciency for identifying the number of leptons appropriate for a given category,triggeris the efficiency for the event to pass the trigger requirements, andgeom-kinis the efficiency for the leptons to fall within the geometric acceptance of the detector and for the events to pass all kinematic re- quirements for each signature. The total efficiencies times branching ratios are listed in Table I. The lepton identifi- cation efficiencies are measured using Z!ee= data.
D. ACOSTAet al. PHYSICAL REVIEW D71,091105 (2005)
091105-4
The Z!eeevents are selected with one identified elec- tron and a second deposition of energy in the electromag- netic calorimeter and an associated track. The Z! events are selected with one identified muon and a second track. The lepton pairs are required to have an invariant mass consistent with aZand tracks of opposite charge. The unbiased lepton is used to measure the identification effi- ciency. The trigger efficiencies are measured using data from independent trigger paths. The geometric and kine- matic efficiencies are determined using a PYTHIA event generator [18] with a GEANT-based detector simulation [19]. Table I also shows the expected numbers ofZZ and ZW events, each calculated using totalR
Ldt, where is the aforementioned NLO theoretical cross section. In each of the three categories a relatively small, but non-neglegible, fraction of the total efficiency is due to final-state tau leptons decaying to electrons and muons.
Overall, we expect 2:310:29 ZZ plus ZW events in 19412 pb1 of data.
The systematic uncertainties associated with the signal acceptances are dominated by the Monte Carlo simulation of6EsigT in the two-lepton category. This uncertainty is esti- mated by comparing distributions of6EsigT between data and Monte Carlo in inclusiveW events, where neutrinos from the W decays produce large 6EsigT . Relative to the signal acceptance, the uncertainty due to6EsigT is 10% forZZand 6% for ZW. The other systematic uncertainties include those from lepton identification efficiencies (1%), trigger efficiencies (1%), the efficiency of the zero or one jet requirement (2%), dependence on different PDF’s (2%), and the calorimeter energy scale and resolution (3%). The total uncertainty in the efficiency estimate is 11% forZZ and 8% forZW.
Backgrounds to theZZ andZW events are determined using a combination of data and Monte Carlo simulations.
The WW, Drell-Yan, and tt background estimates are obtained using PYTHIA Monte Carlo samples with the
expected numbers of events normalized to the theoretical cross sections: 12.4 pb forWWfrom the MCFM program, 330 pb for Drell-Yan from PYTHIA (M =Z0 >
30 GeV=c2 and including a K-factor of 1.4 [20]), and 7 pb for tt[21]. A systematic uncertainty of 14% on the WWbackground results from the same effects that lead to the uncertainties on the ZZ and ZW acceptances. The Drell-Yan background has a 50% uncertainty from two main sources: 35% from the modeling of6EsigT , and another comparable amount from(6ET, lepton/jet). The first is estimated from the comparison of 6EsigT distributions be- tween Drell-Yan data and Monte Carlo, and the second from the observed change in efficiency of the (6ET, lepton/jet) requirement after adjusting the jet energy scale.
Thettbackground has a 15% uncertainty due primarily to the uncertainty in the jet energy scale.
The fake-lepton background is obtained entirely using data. First, the probability for a jet to be misidentified as an electron or muon (fake rate) is estimated from jet-triggered data samples after subtracting real leptons fromW andZ decays. The lepton fake rates are averaged over four samples with increasingly harder jet ET spectra. The ob- served differences between the jet samples are used to estimate the uncertainties in the lepton fake rates. The fake-lepton background is then determined by applying these fake rates to jets in lepton-triggered events which would have passed the event selection had one jet faked a lepton. This background has a 41% uncertainty, dominated by the uncertainty associated with the lepton fake rates.
The backgrounds in the three event categories are summa- rized in Table I.
After all selection criteria we observe 3 events in the data,1all of them in the two-lepton plus6ETcategory (2ee TABLE I. The expected contributions from SM ZZ, ZW and background sources in 194 pb1, and the observed number of candidates in the data. The parentheses show the total efficiency times branching ratio for acceptingZZorZWevents. Systematic and statistical uncertainties, and the uncertainties of theZZandZWNLO cross sections, are included.
Process 4 leptons 3 leptons 2 leptons Combined
ZZ 0:060:01 0:130:01 0:690:11 0:880:13
(ZZ103) (0.22) (0.48) (2.56) (3.26)
ZW 0:780:06 0:650:10 1:430:16
(ZW103) ( ) (1.10) (0.92) (2.02)
Total Signal 0:060:01 0:910:07 1:340:21 2:310:29
WW 0:400:07 0:400:07
Fake 0:010:02 0:070:06 0:210:12 0:290:16
Drell-Yan 0:310:17 0:310:17
tt 0:020:01 0:020:01
Total Background 0:010:02 0:070:06 0:940:22 1:020:24
SignalBackground 0:070:02 0:980:09 2:280:35 3:330:42
Data 0 0 3 3
1Another event passes all the requirements forZZ!eeeein the four-lepton category, except for an isolation cut on one electron [22].
and 1 ), compared to a SM signal plus background expectation of 3:330:42 events. In Fig. 1 we present distributions of leptonpT andin the two-lepton plus6ET category, comparing data to SM expectations. The proba- bility for the background of1:020:24events to fluctuate to give three or more events is 9%. Therefore, we set a 95%
confidence level upper limit on theZZandZW combined cross section by applying a Bayesian method [23] with a flat prior cross section probability above zero. Using the Poisson statistics for the data and including the assumed Gaussian uncertainties in the expected signal and back- ground, we find that the ZZ and ZW combined cross section is less than 15.2 pb at the 95% confidence level.
Using this analysis we conclude that about1 fb1of data is needed for a3measurement of the SM cross section for ZZZWproduction.
In summary, a search forZZandZW production inpp collisions atps
1:96 TeVhas been performed using the leptonic decays of the vector bosons. In a data sample corresponding to an integrated luminosity of194 pb1, 3 candidates are found with an expected background of 1:020:24events. The predicted number ofZZandZW events is2:310:29. A 95% confidence level limit on the sum of the production cross sections for pp !ZZ and pp !ZW is measured to be 15.2 pb, consistent with the standard model prediction of5:00:4 pb.
We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions.
This work was supported by the U.S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Foundation; the A. P. Sloan Foundation; the Bundesministerium fu"r Bildung und Forschung, Germany; the Korean Science and Engineering Foundation and the Korean Research Foundation; the Particle Physics and Astronomy Research Council and the Royal Society, UK; the Russian Foundation for Basic Research; the Comision Interministerial de Ciencia y Tecnologia, Spain; and in part by the European Community’s Human Potential Programme under contract No. HPRN-CT-2002-00292, Probe for New Physics.
[1] J. Ellison and J. Wudka, Annu. Rev. Nucl. Part. Sci.48, 33 (1998).
[2] V. Abazov et al. (D0 Collaboration), hep-ex/0410066 [Phys. Rev. Lett. (to be published)].
[3] D0 Collaboration, B. Abbott et al., Phys. Rev. D 57, R3817 (1998).
[4] B. Abbott et al. (D0 Collaboration), Phys. Rev. D 60, 072002 (1999).
[5] B. Abbott et al. (D0 Collaboration), Phys. Rev. D 62, 052005 (2000).
[6] F. Abe et al.(CDF Collaboration), Phys. Rev. Lett. 75, 1017 (1995).
[7] D. Acostaet al.(CDF Collaboration), Phys. Rev. Lett.94, 041803 (2005).
[8] D. Acosta et al. (CDF Collaboration), hep-ex/0501050 [Phys. Rev. Lett. (to be published)].
[9] R. Barate et al. (ALEPH Collaboration), Phys. Lett. B 469, 287 (1999); G. Abbiendiet al.(OPAL Collaboration), Phys. Lett. B476, 256 (2000); P. Abreuet al.(DELPHI Collaboration), Eur. Phys. J. C30, 447 (2003); P. Achard et al.(L3 Collaboration), Phys. Lett. B572, 133 (2003).
[10] LEP Collaborations, ALEPH Collaboration, DELPHI Collaboration, L3 Collaboration, OPAL Collaboration,
LEP Electroweak Working Group, and SLD Heavy Flavour Working Group, hep-ex/0212036.
[11] S. Klimenko, J. Konigsberg, and T. M. Liss, FERMILAB- FN-0741, 2003 (unpublished).
[12] CDF uses a (z,,) coordinate system, where thez-axis is in the direction of the proton beam, andandare the azimuthal and polar angles, respectively. The pseudora- pidityis defined aslntan2 . The transverse momen- tum of a charged particle is pTpsin, where p represents the measured momentum of the track. The analogous quantity using calorimeter energies, defined asETEsin, is called transverse energy.
[13] R. Blairet al.(CDF Collaboration), FERMILAB-PUB-96- 390-E (unpublished).
[14] C. Issever, AIP Conf. Proc.670, 371 (2003).
[15] J. M. Campbell and R. K. Ellis, Phys. Rev. D60, 113006 (1999).
[16] W. Gieleet al., hep-ph/0204316.
[17] F. Abeet al.(CDF Collaboration), Phys. Rev. D45, 1448 (1992).
[18] T. Sjostrand et al., Comput. Phys. Commun. 135, 238 (2001).
[19] R. Brun and F. Carminati, CERN Program Library Long
(GeV/c) Lepton pT 20 30 40 50 60 70 80 90 100
Leptons / (10 GeV/c)
0 0.5 1 1.5 2 2.5 3
3.5 Data
(ZZ+ZW)+bkgd bkgd (a)
η Lepton -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
Leptons / 0.5
0 0.5 1 1.5 2 2.5 3
3.5 Data
(ZZ+ZW)+bkgd bkgd (b)
FIG. 1. Distributions of (a) leptonpTand (b) leptonof the candidate data events, and the expected SM contributions in the two-lepton plus6ETcategory.
D. ACOSTAet al. PHYSICAL REVIEW D71,091105 (2005)
091105-6
Writeup W5013, 1993 (unpublished).
[20] F. Abe et al. (CDF Collaboration), Phys. Rev. D 59, 052002 (1999).
[21] M. Cacciari, S. Frixione, M. L. Mangano, P. Nason, and G.
Ridolfi, J. High Energy Phys. 04 (2004) 068.
[22] D. Acostaet al.(CDF Collaboration), Phys. Rev. Lett.94, 101802 (2005).
[23] I. Bertram et al., Fermilab-TM-2104 (unpublished); J.
Conway, CERN 2000-005, p. 247, 2000 (unpublished);
K. Hagiwaraet al., Phys. Rev. D66, 010001 (2002).
