Article
Reference
Precise Measurement of the Top-Quark Mass in the Lepton + Jets Topology at CDF II
CDF Collaboration
CAMPANELLI, Mario (Collab.), et al.
Abstract
We present a measurement of the mass of the top quark from proton-antiproton collisions recorded at the CDF experiment in Run II of the Fermilab Tevatron. We analyze events from the single lepton plus jets final state (tt→W+bW−b→lνbqq′b). The top-quark mass is extracted using a direct calculation of the probability density that each event corresponds to the tt final state. The probability is a function of both the mass of the top quark and the energy scale of the calorimeter jets, which is constrained in situ by the hadronic W boson mass. Using 167 events observed in 955 pb−1 of integrated luminosity, we achieve the single most precise measurement of the top-quark mass, 170.8±2.2(stat.)±1.4(syst.) GeV/c2.
CDF Collaboration, CAMPANELLI, Mario (Collab.), et al . Precise Measurement of the
Top-Quark Mass in the Lepton + Jets Topology at CDF II. Physical Review Letters , 2007, vol.
99, no. 18, p. 182002
DOI : 10.1103/PhysRevLett.99.182002
Available at:
http://archive-ouverte.unige.ch/unige:38434
Disclaimer: layout of this document may differ from the published version.
1 / 1
Precise Measurement of the Top-Quark Mass in the Lepton Jets Topology at CDF II
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,9A. Lister,7D. O. Litvintsev,17T. Liu,17N. S. Lockyer,45A. Loginov,60M. Loreti,43R.-S. Lu,1
D. Lucchesi,43P. Lujan,29P. Lukens,17G. Lungu,18L. Lyons,42J. Lys,29R. Lysak,14E. Lytken,48P. Mack,26 D. MacQueen,34R. Madrak,17K. Maeshima,17K. Makhoul,33T. Maki,23P. Maksimovic,25S. Malde,42S. Malik,31 G. Manca,30A. Manousakis,15,aF. Margaroli,5R. Marginean,17C. Marino,26C. P. Marino,24A. Martin,60M. Martin,25 V. Martin,21,gM. Martı´nez,3R. Martı´nez-Balları´n,32T. Maruyama,55P. Mastrandrea,51T. Masubuchi,55H. Matsunaga,55 M. E. Mattson,58R. Mazini,34P. Mazzanti,5K. S. McFarland,49P. McIntyre,53R. McNulty,30,fA. Mehta,30P. Mehtala,23 S. Menzemer,11,hA. Menzione,46P. Merkel,48C. Mesropian,50A. Messina,36T. Miao,17N. Miladinovic,6J. Miles,33 R. Miller,36C. Mills,10M. Milnik,26A. Mitra,1G. Mitselmakher,18A. Miyamoto,27S. Moed,20N. Moggi,5B. Mohr,8
C. S. Moon,28R. Moore,17M. Morello,46P. Movilla Fernandez,29J. Mu¨lmensta¨dt,29A. Mukherjee,17Th. Muller,26
R. Mumford, P. Murat, M. Mussini, J. Nachtman, A. Nagano, J. Naganoma, K. Nakamura, I. Nakano, A. Napier,56V. Necula,16C. Neu,45M. S. Neubauer,9J. Nielsen,29,nL. Nodulman,2O. Norniella,3E. Nurse,31S. H. Oh,16
Y. D. Oh,28I. Oksuzian,18T. Okusawa,41R. Oldeman,30R. Orava,23K. Osterberg,23C. Pagliarone,46E. Palencia,11 V. Papadimitriou,17A. Papaikonomou,26A. A. Paramonov,13B. Parks,39S. Pashapour,34J. Patrick,17G. Pauletta,54 M. Paulini,12C. Paus,33D. E. Pellett,7A. Penzo,54T. J. Phillips,16G. Piacentino,46J. Piedra,44L. Pinera,18K. Pitts,24
C. Plager,8L. Pondrom,59X. Portell,3O. Poukhov,15N. Pounder,42F. Prakoshyn,15A. Pronko,17J. Proudfoot,2 F. Ptohos,19,eG. Punzi,46J. Pursley,25J. Rademacker,42,bA. Rahaman,47V. Ramakrishnan,59N. Ranjan,48I. Redondo,32 B. Reisert,17V. Rekovic,37P. Renton,42M. Rescigno,51S. Richter,26F. Rimondi,5L. Ristori,46A. Robson,21T. Rodrigo,11 E. Rogers,24S. Rolli,56R. Roser,17M. Rossi,54R. Rossin,10P. Roy,34A. Ruiz,11J. Russ,12V. Rusu,13H. Saarikko,23 A. Safonov,53W. K. Sakumoto,49G. Salamanna,51O. Salto´,3L. Santi,54S. Sarkar,51L. Sartori,46K. Sato,17P. Savard,34
A. Savoy-Navarro,44T. Scheidle,26P. Schlabach,17E. E. Schmidt,17M. P. Schmidt,60M. Schmitt,38T. Schwarz,7 L. 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;
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
182002-2
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 29 March 2007; published 31 October 2007)
We present a measurement of the mass of the top quark from proton-antiproton collisions recorded at the CDF experiment in Run II of the Fermilab Tevatron. We analyze events from the single lepton plus jets final state (tt!WbWb!lbqq0b). The top-quark mass is extracted using a direct calculation of the probability density that each event corresponds to thettfinal state. The probability is a function of both the mass of the top quark and the energy scale of the calorimeter jets, which is constrainedin situby the hadronicWboson mass. Using 167 events observed in955 pb1of integrated luminosity, we achieve the single most precise measurement of the top-quark mass,170:82:2stat: 1:4syst:GeV=c2. DOI:10.1103/PhysRevLett.99.182002 PACS numbers: 14.65.Ha, 12.15.Ff, 13.85.Qk
The top quark is the heaviest known elementary particle.
Its large mass plays an important role in loop corrections to several electroweak observables predicted by the standard model. In conjunction with measurements of theW boson mass, a precise measurement of the top-quark mass, mt,
constrains the mass of the as yet unobserved Higgs boson [1]. Moreover, by comparing precision electroweak mea- surements to predictions including the relevant loop cor- rections, a precise measurement of mt can help constrain contributions from physics beyond the standard model.
Measuringmtto the highest achievable precision is there- fore one of the main goals of the experiments operating at the Fermilab Tevatron collider.
At the Tevatron, top quarks are mainly produced in pairs.
They decay essentially 100% of the time into a W boson and abquark, with theW decaying into quarks or leptons.
The result presented here uses the leptonjets channel, where oneWdecays into two quarks and the other decays to an electron or a muon and the corresponding neutrino. In the past, this channel has provided the most precise mea- surements ofmt, and recent measurements can be found in Ref. [2].
In this Letter we report the single most precise measure- ment of the top-quark mass from Tevatron proton- antiproton collisions at
ps
1:96 TeV, using 955 pb1 of integrated luminosity collected with the CDF II detector from February 2002 to March 2006.
The CDF II detector is a general-purpose particle detec- tor and is described in detail elsewhere [3]. It has a sole- noidal charged particle spectrometer, consisting of 7–8 layers of silicon microstrip detectors and a cylindrical drift chamber immersed in a 1.4 T magnetic field, a segmented sampling calorimeter, and a set of charged particle detec- tors outside the calorimeter used to identify muon candi- dates. We use a right-handed cylindrical coordinate system with the origin in the center of the detector, whereand are the polar and azimuthal angles, respectively, and pseu- dorapidity is defined as lntan=2. Transverse en- ergy and momentum are ET Esin and pT psin, respectively, whereEandpare energy and momentum.
Events in the leptonjets decay channel are selected to have a single, isolated electron or muon candidate with large transverse energy, large imbalance in transverse mo- mentum in the event (missing transverse energy [4], E6 T) as expected from the undetectable neutrino, and exactly four jets with large transverse energy. Jets are recon- structed using a cone algorithm with radius R
2 2
p 0:4. Of these jets, we require at least one to have originated from a bquark by using an algo- rithm that identifies a long-lived B hadron through the presence of a displaced vertex (b tag) [5]. Backgrounds to the tt signal arise from multijet QCD production (non-W), W production in association with jets (W jets), and electroweak backgrounds (EWK) composed of diboson (WW,WZ,ZZ) and single top production. W jets background events include jets with real bflavor as well as light flavor jets incorrectly identified asbjets. To remove the non-W backgrounds, whereE6 T is due to mis- measured jet energies, we require E6 T not to be aligned with the highest energy jet by a suitable requirement on between this jet and E6 T. Table I summarizes the selection criteria used in this analysis, and a more detailed description can be found in Ref. [6]. We select 167 events of which we expect about 85% to be ttevents. Table II shows the expected sample composition determined with
318 pb1 [6], scaled to955 pb1 and assuming attcross section of 8.0 pb. Residual differences due to this scaling are absorbed in the systematic background uncertainty.
We analyze the selected events using a likelihood tech- nique that relies on calculations of probability densities based on matrix elements for the signal (tt) and dominant background (Wjets) processes [7]. The backgrounds other than Wjets are found to be adequately described by the Wjets probability density. Given a set of ob- served variables, x, and underlying partonic quantities,y, the signal and background probability densities are con- structed by integrating over the appropriate parton-level differential cross section,dy=dy, convolved with parton distribution functions (PDFs) and detector resolution ef- fects:
Px X
jet perm:
Z dy
dy fq1fq2dq1dq2Wx; ydy: (1) The PDFs [fq1andfq2] take into account the flavors of colliding quark and antiquark and are given by CTEQ5L [8]. The detector resolution effects are described by a transfer function Wx; yrelating xtoy. The momenta of the leptons and the angles of jets and leptons are taken to be exactly measured, and thereforeWx; yfor these quanti- ties is given by the product of Dirac delta functions. The nontrivial part of Wx; y maps parton energies to mea- sured jet energies after correction for instrumental detector effects [9]. This mapping is obtained by parametrizing the jet response in fully simulated tt events created by the Monte Carlo (MC) generator PYTHIA [10] and including the effects of radiation, hadronization, measurement reso- lution, and energy omitted from the jet cone by the recon- struction algorithm. The tt and Wjets probability densities,PttandPWjets, include all possible permutations of matching jets with partons as well as all possible longi- Lepton ET>20 GeV(electron, muon),jj<1 Jets exactly 4 withET>15 GeV,jj<2:0 E6 T >20 GeV, calculated overjj<3:6 btag jets 1from a secondary vertex,jj<1:5 Non-Wveto 0:5 2:5whenE6 T<30 GeV
TABLE II. Background composition and expected number of ttcandidates. All uncertainties are statistical only.
Source Expected number of events
Wjets 14:55:1
non-W 5:22:6
EWK 2:20:5
Total 22:08:2
tt(8:0 pb,mt170 GeV=c2) 145:116:5
Data 167
182002-4
tudinal momenta for the neutrino in the W decay. The permutations are reduced to six or two by exploiting b tagging information (single-tag or double-tag, respec- tively). We use different transfer functions for light quark jets and b jets, depending on the flavor of the parton assigned to the jet. In calculating dy=dy,Ptt uses the leading order matrix element of theqq !ttprocess [11], andPWjets uses the sum of matrix elements of theW4 jets subroutines encoded in theVECBOSMonte Carlo gen- erator [12].
The final state described bydy=dycontains 6 parti- cles, which introduces 20 integration variables in Eq. (1), including the longitudinal momenta of the incoming quarks. By imposing energy-momentum conservation, in conjunction with the Dirac delta functions in Wx; y, we reduce the dimensionality of the remaining integration to five. The integration in PWjets is performed over the energies of the outgoing partons and the invariant mass of the leptonically decayingW using a Monte Carlo tech- nique. In order to reduce the calculation time forPtt, we integrate over the following variables: the invariant masses oft,t, W, andW and the energy of one of the quarks from the hadronic W decay. Our method includes two additional integrations over the transverse momentum components of thettsystem. The integration in Ptt uses the numerical integration codeVEGAS[13].
The largest potential systematic uncertainty in this mea- surement arises from the energy scale of jets. To decrease this uncertainty, we exploit the fact that the hadronically decayingWprovides anin situconstraint of the jet energy scale, as the two jets should form an invariant mass con- sistent with the precisely known mass of theW boson [1].
The jet energy scale and the mass of the top quark are simultaneously determined from a two-dimensional like- lihood that includes their correlation. A salient feature of this method is that the uncertainty due to the jet energy scale will be reduced with increasing statistics. ThusPttis evaluated as a function ofmt and an assumed jet energy scale factorfJESEobsjet=Ejet, whereEobsjet is the observed jet energy andEjetis the true jet energy.
To extractmt andfJES from the data, we build a like- lihood function for N selected events by adding Ptt and PWjets for each event. The combined likelihood is mini- mized with respect to three variables:mt,fJES, andCs, the fraction of events consistent with ourttsignal hypothesis.
The likelihood forN events is given by Lx1; x2;. . .; xN;mt; fJES; Cs
eNCshAttmt;fJESi1CshAWjetsfJESi
YN
i1
CsPttx;mt; fJES 1CsPWjetsx;fJES;
(2) where the first factor arises from the Poisson extension of
the likelihood and normalizes the combined event proba- bility density, andhAirefers to the mean acceptance fortt orWjets events. We use fully simulated MCttandW jets events to determine the functional form ofhAi.PWjets
is evaluated at the central jet energy scale factor,fJES1.
The fJES dependence ofPWjets is determined by varying the inputfJESin MC event samples (fMCJES) and by parame- trizing the average likelihood response as a function of fJES. We use themtdependence of the theoretical leading order ttcross section to normalize Ptt. Because we use a leading order matrix element to calculatePtt, we find that ttevents where at least one of the four reconstructed jets cannot be matched to a parton from the ttdecay within R <0:4 behave like background events. As a conse- quence, a pure sample of ttevents yields Cs of 0.8. The quoted Cs values are corrected for this effect. For each eventPttis evaluated in increments of2 GeV=c2inmtand
2) (GeV/c
MC
mt
165 170 175 180 )2 (GeV/ct - mMC tm
-2 -1 0 1 2
2) (GeV/c
MC
mt
165 170 175 180
σPull
0.8 1 1.2
= 0.94 MC fJES
= 1.00 MC fJES
= 1.06 MC fJES
(a) = 0.26 ± 0.21 (b)
p0 = 1.03 ± 0.02
p0
FIG. 1. Results of pseudoexperiment tests. (a) Difference be- tween the measuredmtand the input top-quark mass in the MC event sample (mMCt ), as a function ofmMCt . (b) Gaussianof pull distributions (see text), as a function of mMCt . The plots include results using MC event samples with different values of fJES (fMCJES). The weighted average p0 is indicated by the solid horizontal line. The dashed line indicates an example of an unbiased result.
2) (GeV/c mt
160 165 170 175 180
JESf
0.95 1 1.05
ln L=0.5
∆
ln L=2.0
∆
ln L=4.5
∆
ln L=8.0
∆
FIG. 2. Contours of likelihood evaluated over the 955 pb1 event sample. Our measurement is indicated by theX.
0.02 in fJES. At each point of this grid we fit the entire sample ofNevents according to Eq. (2) and the most likely value ofCsis determined usingMINUIT[14]. The optimal parameters mt and fJES are obtained by fitting the like- lihood using a two-dimensional Gaussian. The statistical uncertainty onmtincludes the uncertainty onfJES.
The performance of the analysis is tested by extracting mt from MC pseudoexperiments containing tt signal samples with various input top-quark masses (mMCt ) and background samples described in TableII. The signal and electroweak background samples are generated using
HERWIG[10]. TheWjets background is generated using
ALPGEN[10] with hadronization and fragmentation done byHERWIG. The non-W background is extracted from an independent data sample. All of the MC samples are processed by the CDF detector simulation. We construct pseudoexperiments of signal and background events by fluctuating the number of events around the values shown in TableII. Figure1(a)shows that the fitted Gaussian mean mt extracted from 200 pseudoexperiments per point is unbiased with respect to mMCt up to the statistical uncer- tainty of 0:21 GeV=c2, which is taken as a systematic uncertainty. Similar tests are performed for the output of fJES. In this case, we find that a bias of 4% in fJES is present, independent of mt. We correct for this bias to properly interpret the output of fJES. Figure 1(b) shows the top mass pull width, defined as the Gaussianof the top mass residual (mtmMCt ) divided by the uncertainty in each pseudoexperimentmt, as a function ofmMCt . The pull width is3%2%larger than 1 on average, and thus, the statistical uncertainty is scaled up by 3%.
Applying this method to data, we measure the top-quark mass to bemt170:82:2stat:and thefJESscale to be fJES0:990:02stat:, in good agreement with the ref- erence scale from the default CDF calibration [9]. Figure2 shows the fitted two-dimensional likelihood with lnL
contours. The statistical uncertainty is taken from the maximum and minimum mt values on the lnL0:5 contour. We find a correlation coefficient of 0.32 between mtandfJES. The fit yields a signal fraction Cs0:84 0:10stat:, which corresponds to14017ttevents and is consistent with the expectation shown in Table II.
Monte Carlo tests have shown that the resultingmtis stable over a wide range of sample purities. Figure 3 shows comparisons of two representative kinematic quantities between data and simulation using fMCJES0:99 and mMCt 170 GeV=c2.
The sources of systematic uncertainty are listed in Table III. To first order, fJES is already included in the statistical uncertainty, but we also consider a dependence of fJES on the pT and of the jets (residual jet energy scale) using the dependence found in other studies [9]. The other systematic uncertainties listed are explained in detail in Ref. [2]. We also include possible mismodeling of multiple interactions in the simulation at high luminosity.
The sum in quadrature of all systematic uncertainties is 1:4 GeV=c2.
In summary, we present a measurement of the top-quark mass in the leptonjets channel using 955 pb1 of data collected by the CDF experiment. A matrix element analy- sis was used with anin situmeasurement of the jet energy scale. We measure
mt170:82:2stat: 1:4syst:GeV=c2; (3) where the statistical uncertainty includes the uncertainty of 1:5 GeV=c2 due to the jet energy scale. With a total uncertainty of 1.5%, this result is the most precise mea- surement of the top-quark mass to date and is a 35%
improvement over the previous best measurement [2].
We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions.
This work was supported by the US 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
2) (GeV/c mt
100 150 200 250
events / 16 GeV/c
0 20 40
2) (GeV/c mt
100 150 200 250
events / 16 GeV/c
0 20 40
t t background
-1 ) data (955 pb
2) two-jet mass (GeV/c
0 50 100 150
events / 9 GeV/c
0 10 20 30 40
2) two-jet mass (GeV/c
0 50 100 150
events / 9 GeV/c
0 10 20 30
(a) 40 (b) t
= 0.99 MC fJES
FIG. 3. Comparison of two kinematic variables for data and MC usingfMCJES0:99andmMCt 170 GeV=c2. (a) Most prob- able value ofmtfor each event extracted from evaluatingPttat fJES 1. (b) Invariant mass of the pair of jets assigned as W decay products calculated using the most probable permutation at the most probable value ofmtandfJESin each event evaluated fromPtt. The backgrounds contain all contributions shown in TableII.
Source Uncertainty (GeV=c2)
Residual jet energy scale 0.4
bjet energy scale 0.6
Generator 0.2
Initial- and final-state radiation 1.1
PDFs 0.1
Background 0.2
LeptonpT 0.2
btagpTdependence 0.3
Monte Carlo statistics 0.2
Multiple interactions 0.1
Total 1.4
182002-6
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 Science and Technology Facilities Council and the Royal Society, UK; 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 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, Mexico D.F., Mexico.
jVisiting scientist from University of Manchester, Manchester M13 9PL, England.
kVisiting scientist from Nagasaki Institute of Applied Science, Nagasaki, Japan.
lVisiting scientist from University de Oviedo, E-33007 Oviedo, Spain.
mVisiting scientist from University of London, Queen Mary College, 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] For a recent review, see J. Erler and P. Langacker, Phys.
Lett. B592, 1 (2004).
[2] A. Abulenciaet al.(CDF Collaboration), Phys. Rev. Lett.
96, 022004 (2006); Phys. Rev. D73, 092002 (2006);73, 032003 (2006); V. M. Abazov et al. (D0 Collaboration), Phys. Rev. D74, 092005 (2006).
[3] D. Acosta et al.(CDF Collaboration), Phys. Rev. D71, 032001 (2005).
[4] T. Affolderet al.(CDF Collaboration), Phys. Rev. D64, 032002 (2001).
[5] D. Acosta et al.(CDF Collaboration), Phys. Rev. D71, 052003 (2005).
[6] D. Acostaet al.(CDF Collaboration), Phys. Rev. Lett.97, 082004 (2006).
[7] V. M. Abazovet al.(D0 Collaboration), Nature (London) 429, 638 (2004); Phys. Lett. B617, 1 (2005); K. Kondo, J.
Phys. Soc. Jpn. 60, 836 (1991); 57, 4126 (1988); R. H.
Dalitz and G. R. Goldstein, Phys. Rev. D 45, 1531 (1992).
[8] J. Pumplin et al., Nucl. Instrum. Methods Phys. Res., Sect. A447, 1 (2002).
[9] A. Bhatti et al., Nucl. Instrum. Methods Phys. Res., Sect. A566, 375 (2006).
[10] T. Sjostrand, L. Lonnblad, and S. Mrenna, LU Report No. TP 01-21, 2001; arXiv:hep-ph/0108264; G.
Corcella, I. G. Knowles, G. Marchesini, S. Moretti, K.
Odagiri, P. Richardson, M. H. Seymor, and B. R.
Webber, J. High Energy Phys. 01 (2001) 010; M. L.
Mangano, M. Moretti, F. Piccinini, R. Pittau, and A. D.
Polosa, J. High Energy Phys. 07 (2003) 001.
[11] G. Mahlon and S. Parke, Phys. Lett. B411, 173 (1997);
Phys. Rev. D53, 4886 (1996).
[12] F. A. Berends, W. T. Giele, and H. Kuijf, Nucl. Phys.
B321, 39 (1989).
[13] G. P. Lepage, J. Comp. Physiol.27, 192 (1978).
[14] F. James, CERN Program Library Long Writeup No. D506, 1998.
