Article
Reference
First Measurement of the W-Boson Mass in Run II of the Tevatron
CDF Collaboration
CAMPANELLI, Mario (Collab.), et al.
Abstract
WWe present a measurement of the W-boson mass using 200 pb−1 of data collected in pp collisions at s√=1.96 TeV by the CDF II detector at run II of the Fermilab Tevatron. With a sample of 63 964 W→eν candidates and 51 128 W→μν candidates, we measure MW=80 413±34stat±34syst=80 413±48 MeV/c2. This is the most precise single measurement of the W-boson mass to date.
CDF Collaboration, CAMPANELLI, Mario (Collab.), et al . First Measurement of the W-Boson Mass in Run II of the Tevatron. Physical Review Letters , 2007, vol. 99, no. 15, p. 151801
DOI : 10.1103/PhysRevLett.99.151801
Available at:
http://archive-ouverte.unige.ch/unige:38399
Disclaimer: layout of this document may differ from the published version.
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First Measurement of the W -Boson Mass in Run II of the Tevatron
T. Aaltonen,23A. Abulencia,24J. Adelman,13T. Affolder,10T. Akimoto,55M. G. Albrow,17S. Amerio,43D. Amidei,35 A. Anastassov,52K. Anikeev,17A. Annovi,19J. Antos,14M. Aoki,55G. Apollinari,17T. Arisawa,57A. Artikov,15 W. Ashmanskas,17A. Attal,3A. Aurisano,53F. Azfar,42P. Azzi-Bacchetta,43P. Azzurri,46N. Bacchetta,43W. Badgett,17
A. Barbaro-Galtieri,29V. E. Barnes,48B. A. Barnett,25S. Baroiant,7V. Bartsch,31G. Bauer,33P.-H. Beauchemin,34 F. Bedeschi,46S. Behari,25G. Bellettini,46J. Bellinger,59A. Belloni,33D. Benjamin,16A. Beretvas,17J. Beringer,29 T. Berry,30A. Bhatti,50M. Binkley,17D. Bisello,43I. Bizjak,31R. E. Blair,2C. Blocker,6B. Blumenfeld,25A. Bocci,16
A. Bodek,49V. Boisvert,49G. Bolla,48A. Bolshov,33D. Bortoletto,48J. Boudreau,47A. Boveia,10B. Brau,10 L. Brigliadori,5C. Bromberg,36E. Brubaker,13J. Budagov,15H. S. Budd,49S. Budd,24K. Burkett,17G. Busetto,43 P. Bussey,21A. Buzatu,34K. L. Byrum,2S. Cabrera,16,qM. Campanelli,20M. Campbell,35F. Canelli,17A. Canepa,45 S. Carrillo,18,iD. Carlsmith,59R. Carosi,46S. Carron,34B. Casal,11M. Casarsa,54A. Castro,5P. Catastini,46D. Cauz,54 M. Cavalli-Sforza,3A. Cerri,29L. Cerrito,31,mS. H. Chang,28Y. C. Chen,1M. Chertok,7G. Chiarelli,46G. Chlachidze,17
F. Chlebana,17I. Cho,28K. Cho,28D. Chokheli,15J. P. Chou,22G. Choudalakis,33S. H. Chuang,52K. Chung,12 W. H. Chung,59Y. S. Chung,49M. Cilijak,46C. I. Ciobanu,24M. A. Ciocci,46A. Clark,20D. Clark,6M. Coca,16 G. Compostella,43M. E. Convery,50J. Conway,7B. Cooper,31K. Copic,35M. Cordelli,19G. Cortiana,43F. Crescioli,46 C. Cuenca Almenar,7,qJ. Cuevas,11,lR. Culbertson,17J. C. Cully,35S. DaRonco,43M. Datta,17S. D’Auria,21T. Davies,21
D. Dagenhart,17P. de Barbaro,49S. De Cecco,51A. Deisher,29G. De Lentdecker,49,cG. De Lorenzo,3M. Dell’Orso,46 F. Delli Paoli,43L. Demortier,50J. Deng,16M. Deninno,5D. De Pedis,51P. F. Derwent,17G. P. Di Giovanni,44C. Dionisi,51
B. Di Ruzza,54J. R. Dittmann,4M. D’Onofrio,3C. Do¨rr,26S. Donati,46P. Dong,8J. Donini,43T. Dorigo,43S. Dube,52 J. Efron,39R. Erbacher,7D. Errede,24S. Errede,24R. Eusebi,17H. C. Fang,29S. Farrington,30I. Fedorko,46W. T. Fedorko,13
R. G. Feild,60M. Feindt,26J. P. Fernandez,32R. Field,18G. Flanagan,48R. Forrest,7S. Forrester,7M. Franklin,22 J. C. Freeman,29I. Furic,13M. Gallinaro,50J. Galyardt,12J. E. Garcia,46F. Garberson,10A. F. Garfinkel,48C. Gay,60 H. Gerberich,24D. Gerdes,35S. Giagu,51P. Giannetti,46K. Gibson,47J. L. Gimmell,49C. Ginsburg,17N. Giokaris,15,a M. Giordani,54P. Giromini,19M. Giunta,46G. Giurgiu,25V. Glagolev,15D. Glenzinski,17M. Gold,37N. Goldschmidt,18
J. Goldstein,42,bA. Golossanov,17G. Gomez,11G. Gomez-Ceballos,33M. Goncharov,53O. Gonza´lez,32I. Gorelov,37 A. T. Goshaw,16K. Goulianos,50A. Gresele,43S. Grinstein,22C. Grosso-Pilcher,13R. C. Group,17U. Grundler,24 J. Guimaraes da Costa,22Z. Gunay-Unalan,36C. Haber,29K. Hahn,33S. R. Hahn,17E. Halkiadakis,52A. Hamilton,20
B.-Y. Han,49J. Y. Han,49R. Handler,59F. Happacher,19K. Hara,55D. Hare,52M. Hare,56S. Harper,42R. F. Harr,58 R. M. Harris,17M. Hartz,47K. Hatakeyama,50J. Hauser,8C. Hays,42M. Heck,26A. Heijboer,45B. Heinemann,29 J. Heinrich,45C. Henderson,33M. Herndon,59J. Heuser,26D. Hidas,16C. S. Hill,10,bD. Hirschbuehl,26A. Hocker,17
A. Holloway,22S. Hou,1M. Houlden,30S.-C. Hsu,9B. T. Huffman,42R. E. Hughes,39U. Husemann,60J. Huston,36 J. Incandela,10G. Introzzi,46M. Iori,51A. Ivanov,7B. Iyutin,33E. James,17D. Jang,52B. Jayatilaka,16D. Jeans,51 E. J. Jeon,28S. Jindariani,18W. Johnson,7M. Jones,48K. K. Joo,28S. Y. Jun,12J. E. Jung,28T. R. Junk,24T. Kamon,53
P. E. Karchin,58Y. Kato,41Y. Kemp,26R. Kephart,17U. Kerzel,26V. Khotilovich,53B. Kilminster,39D. H. Kim,28 H. S. Kim,28J. E. Kim,28M. J. Kim,17S. B. Kim,28S. H. Kim,55Y. K. Kim,13N. Kimura,55L. Kirsch,6S. Klimenko,18
M. Klute,33B. Knuteson,33B. R. Ko,16K. Kondo,57D. J. Kong,28J. Konigsberg,18A. Korytov,18A. V. Kotwal,16 A. C. Kraan,45J. Kraus,24M. Kreps,26J. Kroll,45N. Krumnack,4M. Kruse,16V. Krutelyov,10T. Kubo,55S. E. Kuhlmann,2
T. Kuhr,26N. P. Kulkarni,58Y. Kusakabe,57S. Kwang,13A. T. Laasanen,48S. Lai,34S. Lami,46S. Lammel,17 M. Lancaster,31R. L. Lander,7K. Lannon,39A. Lath,52G. Latino,46I. Lazzizzera,43T. LeCompte,2J. Lee,49J. Lee,28
Y. J. Lee,28S. W. Lee,53,oR. Lefe`vre,20N. Leonardo,33S. Leone,46S. Levy,13J. D. Lewis,17C. Lin,60C. S. Lin,17 M. Lindgren,17E. Lipeles,9T. M. Liss,24A. Lister,7D. O. Litvintsev,17T. Liu,17N. S. Lockyer,45A. Loginov,60 M. Loreti,43R.-S. Lu,1D. Lucchesi,43P. Lujan,29P. Lukens,17G. Lungu,18L. Lyons,42J. Lys,29R. Lysak,14E. Lytken,48
P. Mack,26D. MacQueen,34R. Madrak,17K. Maeshima,17K. Makhoul,33T. Maki,23P. Maksimovic,25S. Malde,42 S. Malik,31G. Manca,30A. Manousakis,15,aF. Margaroli,5R. Marginean,17C. Marino,26C. P. Marino,24A. Martin,60 M. Martin,25V. Martin,21,gM. Martı´nez,3R. Martı´nez-Balları´n,32T. Maruyama,55P. Mastrandrea,51T. Masubuchi,55
H. Matsunaga,55M. E. Mattson,58R. Mazini,34P. Mazzanti,5K. S. McFarland,49P. McIntyre,53R. McNulty,30,f A. Mehta,30P. Mehtala,23S. Menzemer,11,hA. Menzione,46P. Merkel,48C. Mesropian,50A. Messina,36T. Miao,17
N. Miladinovic,6J. Miles,33R. Miller,36C. Mills,10M. Milnik,26A. Mitra,1G. Mitselmakher,18A. Miyamoto,27 S. Moed,20N. Moggi,5B. Mohr,8C. S. Moon,28R. Moore,17M. Morello,46P. Movilla Fernandez,29J. Mu¨lmensta¨dt,29
A. Mukherjee, Th. Muller, R. Mumford, P. Murat, M. Mussini, J. Nachtman, A. Nagano, J. Naganoma, K. Nakamura,55I. Nakano,40A. Napier,56V. Necula,16C. Neu,45M. S. Neubauer,9J. Nielsen,29,nL. Nodulman,2 O. Norniella,3E. Nurse,31S. H. Oh,16Y. D. Oh,28I. Oksuzian,18T. Okusawa,41R. Oldeman,30R. Orava,23K. Osterberg,23 C. Pagliarone,46E. Palencia,11V. Papadimitriou,17A. Papaikonomou,26A. A. Paramonov,13B. Parks,39S. Pashapour,34 J. Patrick,17G. Pauletta,54M. Paulini,12C. Paus,33D. E. Pellett,7A. Penzo,54T. J. Phillips,16G. Piacentino,46J. Piedra,44 L. Pinera,18K. Pitts,24C. Plager,8L. Pondrom,59X. Portell,3O. Poukhov,15N. Pounder,42F. Prakoshyn,15A. Pronko,17 J. Proudfoot,2F. Ptohos,19,eG. Punzi,46J. Pursley,25J. Rademacker,42,bA. Rahaman,47V. Ramakrishnan,59N. Ranjan,48 I. Redondo,32B. Reisert,17V. Rekovic,37P. Renton,42M. Rescigno,51S. Richter,26F. Rimondi,5L. Ristori,46A. Robson,21 T. Rodrigo,11E. Rogers,24S. Rolli,56R. Roser,17M. Rossi,54R. Rossin,10P. Roy,34A. Ruiz,11J. Russ,12V. Rusu,13 H. Saarikko,23A. Safonov,53W. K. Sakumoto,49G. Salamanna,51O. Salto´,3L. Santi,54S. Sarkar,51L. Sartori,46K. Sato,17
P. Savard,34A. Savoy-Navarro,44T. Scheidle,26P. Schlabach,17E. E. Schmidt,17M. P. Schmidt,60M. Schmitt,38 T. Schwarz,7L. Scodellaro,11A. L. Scott,10A. Scribano,46F. Scuri,46A. Sedov,48S. Seidel,37Y. Seiya,41A. Semenov,15
L. Sexton-Kennedy,17A. Sfyrla,20S. Z. Shalhout,58M. D. Shapiro,29T. Shears,30P. F. Shepard,47D. Sherman,22 M. Shimojima,55,kM. Shochet,13Y. Shon,59I. Shreyber,20A. Sidoti,46P. Sinervo,34A. Sisakyan,15A. J. Slaughter,17 J. Slaunwhite,39K. Sliwa,56J. R. Smith,7F. D. Snider,17R. Snihur,34M. Soderberg,35A. Soha,7S. Somalwar,52V. Sorin,36
J. Spalding,17F. Spinella,46T. Spreitzer,34P. Squillacioti,46M. Stanitzki,60A. Staveris-Polykalas,46R. St. Denis,21 B. Stelzer,8O. Stelzer-Chilton,42D. Stentz,38J. Strologas,37D. Stuart,10J. S. Suh,28A. Sukhanov,18H. Sun,56I. Suslov,15
T. Suzuki,55A. Taffard,24,pR. Takashima,40Y. Takeuchi,55R. Tanaka,40M. Tecchio,35P. K. Teng,1K. Terashi,50 J. Thom,17,dA. S. Thompson,21E. Thomson,45P. Tipton,60V. Tiwari,12S. Tkaczyk,17D. Toback,53S. Tokar,14 K. Tollefson,36T. Tomura,55D. Tonelli,46S. Torre,19D. Torretta,17S. Tourneur,44W. Trischuk,34S. Tsuno,40Y. Tu,45 N. Turini,46F. Ukegawa,55S. Uozumi,55S. Vallecorsa,20N. van Remortel,23A. Varganov,35E. Vataga,37F. Vazquez,18,i
G. Velev,17C. Vellidis,46,aG. Veramendi,24V. Veszpremi,48M. Vidal,32R. Vidal,17I. Vila,11R. Vilar,11T. Vine,31 M. Vogel,37I. Vollrath,34I. Volobouev,29,oG. Volpi,46F. Wu¨rthwein,9P. Wagner,53R. G. Wagner,2R. L. Wagner,17 J. Wagner,26W. Wagner,26R. Wallny,8S. M. Wang,1A. Warburton,34D. Waters,31M. Weinberger,53W. C. Wester III,17
B. Whitehouse,56D. Whiteson,45,pA. B. Wicklund,2E. Wicklund,17G. Williams,34H. H. Williams,45P. Wilson,17 B. L. Winer,39P. Wittich,17,dS. Wolbers,17C. Wolfe,13T. Wright,35X. Wu,20S. M. Wynne,30A. Yagil,9K. Yamamoto,41
J. Yamaoka,52T. Yamashita,40C. Yang,60U. K. Yang,13,jY. C. Yang,28W. M. Yao,29G. P. Yeh,17J. Yoh,17K. Yorita,13 T. Yoshida,41G. B. Yu,49I. Yu,28S. S. Yu,17J. C. Yun,17L. Zanello,51A. Zanetti,54I. Zaw,22X. Zhang,24
J. Zhou,52and S. Zucchelli5
(CDF Collaboration)
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
4Baylor University, Waco, Texas 76798, USA
5Istituto Nazionale di Fisica Nucleare, University of Bologna, I-40127 Bologna, Italy
6Brandeis University, Waltham, Massachusetts 02254, USA
7University of California, Davis, Davis, California 95616, USA
8University of California, Los Angeles, Los Angeles, California 90024, USA
9University of California, San Diego, La Jolla, California 92093, USA
10University of California, Santa Barbara, Santa Barbara, California 93106, USA
11Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain
12Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
13Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA
14Comenius University, 842 48 Bratislava, Slovakia; and Institute of Experimental Physics, 040 01 Kosice, Slovakia
15Joint Institute for Nuclear Research, RU-141980 Dubna, Russia
16Duke University, Durham, North Carolina 27708, USA
17Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
18University of Florida, Gainesville, Florida 32611, USA
19Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy
20University of Geneva, CH-1211 Geneva 4, Switzerland
21Glasgow University, Glasgow G12 8QQ, United Kingdom
22Harvard University, Cambridge, Massachusetts 02138, USA
151801-2
23Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014 Helsinki, Finland
24University of Illinois, Urbana, Illinois 61801, USA
25The Johns Hopkins University, Baltimore, Maryland 21218, USA
26Institut fu¨r Experimentelle Kernphysik, Universita¨t Karlsruhe, 76128 Karlsruhe, Germany
27High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305, Japan
28Center for High Energy Physics: Kyungpook National University, Taegu 702-701, Korea;
Seoul National University, Seoul 151-742, Korea;
SungKyunKwan University, Suwon 440-746, Korea
29Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
30University of Liverpool, Liverpool L69 7ZE, United Kingdom
31University College London, London WC1E 6BT, United Kingdom
32Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain
33Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
34Institute of Particle Physics: McGill University, Montre´al, Canada H3A 2T8;
and University of Toronto, Toronto, Canada M5S 1A7
35University of Michigan, Ann Arbor, Michigan 48109, USA
36Michigan State University, East Lansing, Michigan 48824, USA
37University of New Mexico, Albuquerque, New Mexico 87131, USA
38Northwestern University, Evanston, Illinois 60208, USA
39The Ohio State University, Columbus, Ohio 43210, USA
40Okayama University, Okayama 700-8530, Japan
41Osaka City University, Osaka 588, Japan
42University of Oxford, Oxford OX1 3RH, United Kingdom
43Istituto Nazionale di Fisica Nucleare, University of Padova, Sezione di Padova-Trento, I-35131 Padova, Italy
44LPNHE, Universite Pierre et Marie Curie/IN2P3-CNRS, UMR7585, Paris F-75252, France
45University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
46Istituto Nazionale di Fisica Nucleare Pisa, Universities of Pisa, Siena and Scuola Normale Superiore, I-56127 Pisa, Italy
47University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
48Purdue University, West Lafayette, Indiana 47907, USA
49University of Rochester, Rochester, New York 14627, USA
50The Rockefeller University, New York, New York 10021, USA
51Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1, University of Rome ‘‘La Sapienza,’’ I-00185 Roma, Italy
52Rutgers University, Piscataway, New Jersey 08855, USA
53Texas A&M University, College Station, Texas 77843, USA
54Istituto Nazionale di Fisica Nucleare, University of Trieste/Udine, Italy
55University of Tsukuba, Tsukuba, Ibaraki 305, Japan
56Tufts University, Medford, Massachusetts 02155, USA
57Waseda University, Tokyo 169, Japan
58Wayne State University, Detroit, Michigan 48201, USA
59University of Wisconsin, Madison, Wisconsin 53706, USA
60Yale University, New Haven, Connecticut 06520, USA (Received 3 July 2007; published 12 October 2007)
We present a measurement of theW-boson mass using200 pb1of data collected inppcollisions at s
p 1:96 TeVby the CDF II detector at run II of the Fermilab Tevatron. With a sample of 63 964W! ecandidates and 51 128W!candidates, we measure MW80 41334stat34syst80 413 48 MeV=c2. This is the most precise single measurement of theW-boson mass to date.
DOI:10.1103/PhysRevLett.99.151801 PACS numbers: 14.70.Fm, 13.38.Be, 13.85.Qk
The standard model (SM) invokes the Higgs mechanism of spontaneous symmetry breaking to generate mass for the W and Z bosons, which mediate the weak force. The SU2 U1 symmetry of the electroweak interaction predicts the relation between theW- andZ-boson masses and the electromagnetic and weak gauge couplings. The prediction for the W-boson mass MW in terms of the precisely measured Z-boson mass MZ, the Fermi decay constant GF extracted from the muon lifetime measure-
ment, and the electromagnetic couplingat the scaleMZ are given in the ‘‘on-shell’’ scheme by [1]
MW2 @3 c
2 p
GF
1
1c2W1r;
wherecW MW=MZandris the quantum-loop correc- tion. A precise measurement of MW provides a measure- ment of r. In the SM the contributions to r are dominated by the top quark and the Higgs boson loops,
such that MW in conjunction with the top quark mass constrains the massmH of the undiscovered Higgs boson.
An mH constraint, inconsistent with direct searches, can indicate the presence of new physics, such as contributions torfrom supersymmetric particles [2].
The W-boson mass [1] has been measured most pre- cisely by the LEP [3,4] and Tevatron [5] experiments, with the world averageMW 80 39229 MeV=c2[4]. At the Tevatron, W bosons are mainly produced in quark (q0) antiquark (q) annihilation q0q!WX. HereXincludes the QCD radiation that forms the ‘‘hadronic recoil’’ bal- ancing the boson’s transverse momentumpT[6]. TheW !
‘decays, characterized by a high-pTcharged lepton (‘
eor) and neutrino, can be selected with high purity and provide precise mass information.
This analysis [7,8] uses 200 pb1 collected by the CDF II detector [7] inpp collisions atps
1:96 TeVat the Tevatron. CDF II is a magnetic spectrometer sur- rounded by calorimeters and muon detectors. We use the central drift chamber (COT) [9], the central calorimeter [10] with embedded wire chambers [11] at the electromag- netic (EM) shower maximum, and the muon detectors [12]
for identification of muons and electrons withjj<1[6]
and measurement of their four-momenta. The muon (elec- tron) trigger requires a COT track withpT>189GeV=c [6] and matching muon chamber hits (EM calorimeter cluster withET>18 GeV).
In the analysis, we select muons with a COT track matched to muon chamber hits and passing quality require- ments, track pT>30 GeV=c, and a minimum-ionization signal in the calorimeter. Cosmic rays are rejected using COT hit timing [13]. We select electrons with track pT >
18 GeV=c, EM cluster ET>30 GeV [6,7], and passing quality requirements on the COT track and the track- cluster matching. Additional requirements are based on the ratio of the calorimeter energyE to track momentum p (E=pc <2), the ratio of energies detected in the had- ronic and EM calorimetersEHad=EEM<0:1, and the trans- verse shower profile [7]. A veto on the presence of a second lepton suppresses Z-boson background, with negligible loss ofW-boson events. Control samples ofZ-boson events require two oppositely charged leptons with the above criteria.
Thep~T of the hadronic recoil (u) equals the vector sum~
~
uiEisinin^i=c over calorimeter towers [10], with energyEi, polar anglei, and transverse directions speci- fied by unit vectorsn^i. Energy associated with the charged lepton(s) is not included. We imposep~T balance to infer the neutrino’s transverse momentumpT jp~‘Tuj~ [6]
and theW transverse massmT
2p‘TpTp~‘T p~T q
=c.
We requirepT>30 GeV=candjuj~ <15 GeV=cto obtain aWcandidate sample of high purity, whosemT and lepton pT distributions are strongly correlated with MW. The sample consists of 63 964 W !eand 51 128 W! candidates.
The W-boson mass is extracted by performing binned maximum likelihood fits to the distributions ofmT,p‘T, and pT. We generate 800 templates as functions of MW be- tween 80 GeV=c2 and 81 GeV=c2 using a custom Monte Carlo (MC) simulation [7] of boson production and decay, and of the detector response to the lepton(s) and hadronic recoil. The custom MC optimizes computing speed and control of systematic uncertainties. The kine- matics of W- andZ-boson decays are obtained from the
RESBOS [14] program. We tune the nonperturbative form factor inRESBOS, which describes the bosonpT spectrum at lowpT, on the dileptonpT distributions in theZ-boson data. Single photons (final-state radiation) radiated from the final-state leptons are generated according to the
WGRAD program [15]. The final-state radiation photon energies are increased by 10% (with an absolute uncer- tainty of 5%) to account for additional energy loss due to two-photon radiation [16].WGRADis also used to estimate the initial-state QED radiation. We use the CTEQ6M [17]
set of parton distribution functions and their uncertainties.
The custom MC simulation performs a hit-level simula- tion of the lepton track. A fine-grained model of passive material properties is used to calculate ionization and radiative energy loss and multiple Coulomb scattering.
Bremsstrahlung photons and conversion electrons are gen- erated and propagated to the calorimeter. COT hits are generated according to the resolution (150m) and efficiencies measured from muon tracks in , W, and Z-boson decays. A helix fit (with optional beam constraint) is performed to simulate the reconstructed track.
The alignment of the COT is performed using a high- purity sample of high-pT cosmic ray muons. Each muon’s complete trajectory is fit to a single helix [13]. The fits determine the relative locations of the sense wires, includ- ing gravitational and electrostatic displacements, with a precision of a few microns. We constrain remaining mis- alignments, which cause a bias in the track curvature, by comparinghE=pcifor electrons and positrons.
The tracker momentum scale is measured by template fitting theJ= !and!mass peaks. TheJ=
fits are performed in bins of h1=p‘Ti to measure any nonlinearity due to mismodeling of the ionization energy loss and other smaller effects, and in bins ofhcoti to measure the magnetic field nonuniformity. To account for the observed momentum nonlinearity, a downward 6%
correction to the predicted ionization energy loss is applied in the simulation to make the measured J= mass inde- pendent of h1=p‘Ti. The calibration derived from the J= and data yields MZ91 18443stat MeV=c2 (Fig.1) from theZ!data, consistent with the world average [1,4] of91 1882 MeV=c2. The systematic un- certainties due to QED radiative corrections and magnetic field nonuniformity dominate the total uncertainty of 0.02% on the combined momentum scale, derived from theJ= ,, andZ-boson mass fits.
151801-4
We simulate the electron cluster by merging the energies of the primary electron and the proximate bremsstrahlung photons and conversion electrons. The distributions of electron and photon energy loss in the solenoid coil, and leakage into the hadronic calorimeter, are determined us- ingGEANT[18] as a function ofET. The fractional energy resolution is given by the quadrature sum of a sampling
term (13:5%=
ET=GeV
p ) and a constant term 0:89 0:15% applied to the cluster energy, and an additional constant term 8:32:2% applied only to the en- ergies of bremsstrahlung photons and conversion electrons.
The term contributes 1:3% in quadrature to the
effective constant term for the inclusive electron sample.
The distribution of the underlying event energy [7] in the cluster is simulated. We tune on the width of theE=pc peak (Fig.2) of theW-boson sample, andon the width of theZ!eemass peak when both electrons are radiative (E=pc >1:06).
Given the tracker momentum calibration, we fit the E=pc peak in bins of electron ET to determine the elec- tron energy scale and nonlinearity. The position of the E=pcpeak is sensitive to the number of radiation lengths X0 (19%), due to bremsstrahlung upstream of the COT.
We constrain X0 by comparing the fraction of electrons with highE=pcbetween data and simulation. Applying the E=pc-based energy calibration, we fit the Z!ee mass peak and measureMZ91 19067stat MeV=c2(Fig.1), consistent with the world average [1,4]. For maximum precision, the energy scales from theW E=pc fit and the Z!ee mass fit are combined using the best linear un- biased estimate (BLUE) method [19], with a resulting uncertainty that is mostly statistical.
The recoil u~ excludes towers in which the lepton(s) deposit energy. The underlying event energy in these tow- ers is measured from the nearby towers in W-boson data, including its dependence on‘ andu. The resolution of~ u~ has jetlike and underlying event components, with the
1 1.5
0 2000 4000
/(dof) = 17 / 16 χ2
ν)
→ e E/pc (W
Events/0.01
FIG. 2. The distribution ofE=pcfor theW!edata (points) and the best-fit simulation (histogram) including the small jet background (shaded). The arrows indicate the fitting range used for the electron energy calibration. The jet background, which is barely visible on this scale, contributes a negligible uncertainty in the calibrations of the electron energy scale and the amount of radiative material.
) (GeV/c ν)
→e (W u
-15 -10 -5 0 5 10 15
)cEvents / (2 GeV/
0 5000 10000 15000
) (GeV/c ν) µ
→
|u| (W
0 5 10 15
)cEvents / (GeV/
0 5000
FIG. 3. Left panel: Theukdistribution for the electron channel data (points) and simulation (histogram). Right panel: The juj~ distribution for the muon channel. The mean and rms of the histograms agree between data and simulation, within the sta- tistical precisions of1%.
70 80 90 100 110
0 100 200
/(dof) = 34 / 38 χ2
→ ee Z
mee c2
2c
(GeV/ )
Events / (0.5 GeV/ )
70 80 90 100 110
0 200 400
/(dof) = 33 / 30 χ2
µ µ
→ Z
µ
mµ c2
2c
(GeV/ )
Events / (0.5 GeV/ )
FIG. 1. TheZ!ee(top panel) andZ!(bottom panel) mass fits, showing the data (points) and the simulation (histo- gram). The arrows indicate the fitting range.
TABLE I. Fit results and uncertainties for MW. The fit win- dows are65–90 GeV=c2for themTfit and32–48 GeV=cfor the p‘TandpTfits. The 2of the fit is computed using the expected statistical errors on the data points.
Distribution W-boson mass (MeV=c2) 2=dof mTe; 80 49348stat39syst 86=48 p‘Te 80 45158stat45syst 63=62 pTe 80 47357stat54syst 63=62 mT; 80 34954stat27syst 59=48 p‘T 80 32166stat40syst 72=62 pT 80 39666stat46syst 44=62
latter modeled using data triggered on inelastic pp inter- actions. The recoil parametrizations are tuned on the mean and rms of thep~Timbalance between the dileptonp~Tandu~ in Z!‘‘ events. The lepton identification efficiency is measured as a function ofuku~ p~‘T=p‘T using theZ!
‘‘ data, in order to model its effect on the p‘T and pT distributions. Cross-checks of the recoil model using the W-boson data show good agreement (Fig.3).
Backgrounds in the W-boson candidate samples arise from misidentified jets containing high-pT tracks and EM clusters,Z!‘‘where a lepton is not reconstructed and mimics a neutrino,W !,=K decays in flight (DIF), and cosmic rays. Jet, DIF, and cosmic ray backgrounds are estimated from the data to be less than 0.5% combined. The W ! background is 0.9% (0.9%), and the Z!‘‘
background is 6.6% (0.24%) in the muon (electron) chan- nel, as estimated using a detailed GEANT-based detector simulation. The background shapes are obtained using simulation and data-derived distributions.
TableIshows the fit results from themT(Fig.4),p‘T, and pT distributions. These fits are partially uncorrelated and have different systematic uncertainties, thus providing an important cross-check. The fit values were hidden during analysis by adding an unknown offset in the range 100;100MeV=c2. The systematic uncertainties (TableII) were evaluated by fitting MC events to propagate the analysis parameter uncertainties toMW.
The consistency of the fit results (TableI) obtained from the different distributions shows that theW-boson produc- tion, decay, and the hadronic recoil are well modeled. The statistical correlations (evaluated using ensembles of MC events) between the mT and p‘T (pT) fit values is 69%
(68%), and between thep‘T andpT fit values is 27%. We numerically combine (using the BLUE method) the six individually fittedMWvalues, including their correlations, to obtain MW 8041334stat34syst MeV=c2, with
2=dof 4:8=5. The mT, p‘T, and pT fits in the elec- tron (muon) channel contribute weights of 32.3% (47.7%), 8.9% (3.4%), and 6.8% (0.9%), respectively. This estab- lishes ana prioriprocedure to incorporate the information from individual fits. The muon (electron) channel alone yields MW 80 35260 MeV=c2 (MW 80 477 62 MeV=c2) with 2=dof 1:4=20:8=2. ThemT (p‘T, pT) fit results from the muon, and electron channels are consistent with a probability of 7% (18%, 43%), taking into account their correlations.
In conclusion, we report the first measurement of the W-boson mass from run II of the Tevatron. We measure MW 80 41348 MeV=c2, the most precise single mea- surement to date, and we update the world average [4] to MW 80 39825 MeV=c2. This analysis significantly improves in precision over previous Tevatron measure- ments, not only through the increased integrated luminos- ity but also through improved analysis techniques and understanding of systematic uncertainties. As many simu- lation parameters are constrained by data control samples, their uncertainties are statistical in nature and are expected to be reduced with more data. Inclusion of our result in the global electroweak fit [4,7] reduces the predicted mass of the SM Higgs boson by6 GeV=c2 and decreases its range tomH 763324GeV=c2.
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
60 70 80 90 100
0 500 1000
/(dof) = 59 / 48 χ2
mT
ν µ
→ W
2c
c2 (GeV/ )
Events / (0.5 GeV/ )
60 70 80 90 100
0 500 1000 1500
/(dof) = 86 / 48 χ2
mT
ν
→ e W
2c
c2 (GeV/ )
Events / (0.5 GeV/ )
FIG. 4. ThemTdistribution of the data (points) and the best-fit simulation template (histogram) including backgrounds (shaded), for muons (top panel) and electrons (bottom panel).
The arrows indicate the fitting range. The 2=dof for the electron channel distribution receives large contributions from a few bins near65 GeV=c2, which do not bias the mass fit.
the mT fits, which are the most precise. The last column shows the correlated uncertainties.
Systematic W!e W! Common
pTWmodel 3 3 3
QED radiation 11 12 11
Parton distributions 11 11 11
Lepton energy scale 30 17 17
Lepton energy resolution 9 3 0
Recoil energy scale 9 9 9
Recoil energy resolution 7 7 7
uk efficiency 3 1 0
Lepton removal 8 5 5
Backgrounds 8 9 0
Total systematic 39 27 26
Total uncertainty 62 60 26
151801-6
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 Founda- tion; 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 Science and Technology Facilities Coun- cil and the Royal Society, U.K.; the Institut National de Physique Nucleaire et Physique des Particules/CNRS; the Russian Foundation for Basic Research; the Comisio´n Interministerial de Ciencia y Tecnologı´a, Spain; the European Community’s Human Potential Programme;
the European Commission under the Marie Curie Pro- gramme; the Slovak R&D Agency; and the Academy of Finland.
aVisiting scientist from University of Athens, 15784 Athens, Greece.
bVisiting scientist from University of Bristol, Bristol BS8 1TL, United Kingdom.
cVisiting scientist from University Libre de Bruxelles, B-1050 Brussels, Belgium.
dVisiting scientist from Cornell University, Ithaca, NY 14853, USA.
eVisiting scientist from University of Cyprus, Nicosia CY- 1678, Cyprus.
fVisiting scientist from University College Dublin, Dublin 4, Ireland.
gVisiting scientist from University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
hVisiting scientist from University of Heidelberg, D-69120 Heidelberg, Germany.
iVisiting scientist from Universidad Iberoamericana, Ciudad de Me´xico, Mexico.
jVisiting scientist from University of Manchester, Manchester M13 9PL, United Kingdom.
kVisiting scientist from Nagasaki Institute of Applied Science, Nagasaki, Japan.
lVisiting scientist from University de Oviedo, E-33007 Oviedo, Spain.
mVisiting scientist from Queen Mary College, University of London, London E1 4NS, United Kingdom.
nVisiting scientist from University of California, Santa Cruz, Santa Cruz, CA 95064, USA.
oVisiting scientist from Texas Tech University, Lubbock, TX 79409, USA.
pVisiting scientist from University of California, Irvine, Irvine, CA 92697, USA.
qVisiting scientist from IFIC (CSIC-Universitat de Valencia), 46071 Valencia, Spain.
[1] W.-M. Yaoet al., J. Phys. G33, 1 (2006).
[2] S. Heinemeyeret al., J. High Energy Phys. 08 (2006) 052.
[3] S. Schaelet al. (ALEPH Collaboration), Eur. Phys. J. C 47, 309 (2006); G. Abbiendi et al. (OPAL Collabora- tion), Eur. Phys. J. C 45, 307 (2006); P. Achard et al.
(L3 Collaboration), Eur. Phys. J. C 45, 569 (2006);
J. Abdallah et al. (DELPHI Collaboration), Eur.
Phys. J. C (to be published).
[4] J. Alcaraz et al. (LEP Collaborations and LEP Electroweak Working Group), CERN Report No. CERN-PH-EP/2006-042, and references therein.
[5] T. Affolderet al.(CDF Collaboration), Phys. Rev. D64, 052001 (2001); V. M. Abazov et al. (D0 Collaboration), Phys. Rev. D 66, 012001 (2002); B. Abbott et al. (D0 Collaboration), Phys. Rev. D 62, 092006 (2000);
B. Abbott et al. (D0 Collaboration), Phys. Rev. D 58, 092003 (1998); V. M. Abazov et al. (CDF and D0 Collaborations), Phys. Rev. D70, 092008 (2004).
[6] Pseudorapidity is defined as lntan=2], where is the polar angle from the beam axis. Energy (momen- tum) transverse to the beam is denoted asET (pT).
[7] T. Aaltonenet al.(CDF Collaboration), arXiv:0708.3642 [Phys. Rev. D (to be published)].
[8] O. Stelzer-Chilton, Ph.D. thesis, University of Toronto, 2005; I. Vollrath, Ph.D. thesis, University of Toronto, 2006.
[9] T. Affolderet al., Nucl. Instrum. Methods Phys. Res., Sect.
A526, 249 (2004).
[10] F. Abeet al.(CDF Collaboration), Nucl. Instrum. Methods Phys. Res., Sect. A271, 387 (1988).
[11] A. Byon-Wagneret al., IEEE Trans. Nucl. Sci.49, 2567 (2002).
[12] G. Ascoliet al., Nucl. Instrum. Methods Phys. Res., Sect.
A268, 33 (1988).
[13] A. V. Kotwal, H. K. Gerberich, and C. Hays, Nucl.
Instrum. Methods Phys. Res., Sect. A506, 110 (2003).
[14] C. Balazs and C.-P. Yuan, Phys. Rev. D56, 5558 (1997);
G. A. Ladinsky and C.-P. Yuan, Phys. Rev. D50, R4239 (1994); F. Landry, R. Brock, P. M. Nadolsky, and C.-P.
Yuan, Phys. Rev. D67, 073016 (2003).
[15] U. Baur, S. Keller, and D. Wackeroth, Phys. Rev. D59, 013002 (1998).
[16] C. M. Carloni Calame, G. Montagna, O. Nicrosini, and M. Treccani, Phys. Rev. D69, 037301 (2004).
[17] J. Pumplinet al., J. High Energy Phys. 07 (2002) 012.
[18] R. Brun and F. Carminati, CERN Program Library Long Writeup, Report No. W5013, 1993 (unpublished), version 3.15.
[19] L. Lyons, D. Gibaut, and P. Clifford, Nucl. Instrum.
Methods Phys. Res., Sect. A270, 110 (1988).
