First Direct Bound on the Total Width of the Top Quark in ppbar Collisions at sqrt(s) = 1.96 TeV
aa r X i v : . [ h e p - e x ] M a r First Direct Bound on the Total Width of the Top Quark in p ¯ p Collisions at √ s = 1 . TeV
T. Aaltonen, J. Adelman, T. Akimoto, M.G. Albrow, B. ´Alvarez Gonz´alez, S. Amerio u , D. Amidei, A. Anastassov, A. Annovi, J. Antos, G. Apollinari, A. Apresyan, T. Arisawa, A. Artikov, W. Ashmanskas, A. Attal, A. Aurisano, F. Azfar, P. Azzurri s , W. Badgett, A. Barbaro-Galtieri, V.E. Barnes, B.A. Barnett, V. Bartsch, G. Bauer, P.-H. Beauchemin, F. Bedeschi, P. Bednar, D. Beecher, S. Behari, G. Bellettini q , J. Bellinger, D. Benjamin, A. Beretvas, J. Beringer, A. Bhatti, M. Binkley, D. Bisello u , I. Bizjak, R.E. Blair, C. Blocker, B. Blumenfeld, A. Bocci, A. Bodek, V. Boisvert, G. Bolla, D. Bortoletto, J. Boudreau, A. Boveia, B. Brau, A. Bridgeman, L. Brigliadori, C. Bromberg, E. Brubaker, J. Budagov, H.S. Budd, S. Budd, K. Burkett, G. Busetto u , P. Bussey x , A. Buzatu, K. L. Byrum, S. Cabrera p , C. Calancha, M. Campanelli, M. Campbell, F. Canelli, A. Canepa, D. Carlsmith, R. Carosi, S. Carrillo j , S. Carron, B. Casal, M. Casarsa, A. Castro t , P. Catastini r , D. Cauz w , V. Cavaliere r , M. Cavalli-Sforza, A. Cerri, L. Cerrito n , S.H. Chang, Y.C. Chen, M. Chertok, G. Chiarelli, G. Chlachidze, F. Chlebana, K. Cho, D. Chokheli, J.P. Chou, G. Choudalakis, S.H. Chuang, K. Chung, W.H. Chung, Y.S. Chung, C.I. Ciobanu, M.A. Ciocci r , A. Clark, D. Clark, G. Compostella, M.E. Convery, J. Conway, K. Copic, M. Cordelli, G. Cortiana u , D.J. Cox, F. Crescioli q , C. Cuenca Almenar p , J. Cuevas m , R. Culbertson, J.C. Cully, D. Dagenhart, M. Datta, T. Davies, P. de Barbaro, S. De Cecco, A. Deisher, G. De Lorenzo, M. Dell’Orso q , C. Deluca, L. Demortier, J. Deng, M. Deninno, P.F. Derwent, G.P. di Giovanni, C. Dionisi v , B. Di Ruzza w , J.R. Dittmann, M. D’Onofrio, S. Donati q , P. Dong, J. Donini, T. Dorigo, S. Dube, J. Efron, A. Elagin, R. Erbacher, D. Errede, S. Errede, R. Eusebi, H.C. Fang, S. Farrington, W.T. Fedorko, R.G. Feild, M. Feindt, J.P. Fernandez, C. Ferrazza s , R. Field, G. Flanagan, R. Forrest, M. Franklin, J.C. Freeman, I. Furic, M. Gallinaro, J. Galyardt, F. Garberson, J.E. Garcia, A.F. Garfinkel, K. Genser, H. Gerberich, D. Gerdes, A. Gessler, S. Giagu v , V. Giakoumopoulou, P. Giannetti, K. Gibson, J.L. Gimmell, C.M. Ginsburg, N. Giokaris, M. Giordani w , P. Giromini, M. Giunta q , G. Giurgiu, V. Glagolev, D. Glenzinski, M. Gold, N. Goldschmidt, A. Golossanov, G. Gomez, G. Gomez-Ceballos, M. Goncharov, O. Gonz´alez, I. Gorelov, A.T. Goshaw, K. Goulianos, A. Gresele u , S. Grinstein, C. Grosso-Pilcher, R.C. Group, U. Grundler, J. Guimaraes da Costa, Z. Gunay-Unalan, C. Haber, K. Hahn, S.R. Hahn, E. Halkiadakis, B.-Y. Han, J.Y. Han, R. Handler, F. Happacher, K. Hara, D. Hare, M. Hare, S. Harper, R.F. Harr, R.M. Harris, M. Hartz, K. Hatakeyama, J. Hauser, C. Hays, M. Heck, A. Heijboer, B. Heinemann, J. Heinrich, C. Henderson, M. Herndon, J. Heuser, S. Hewamanage, D. Hidas, C.S. Hill c , D. Hirschbuehl, A. Hocker, S. Hou, M. Houlden, S.-C. Hsu, B.T. Huffman, R.E. Hughes, U. Husemann, J. Huston, J. Incandela, G. Introzzi, M. Iori v , A. Ivanov, E. James, B. Jayatilaka, E.J. Jeon, M.K. Jha, S. Jindariani, W. Johnson, M. Jones, K.K. Joo, S.Y. Jun, J.E. Jung, T.R. Junk, T. Kamon, D. Kar, P.E. Karchin, Y. Kato, R. Kephart, J. Keung, V. Khotilovich, B. Kilminster, D.H. Kim, H.S. Kim, J.E. Kim, M.J. Kim, S.B. Kim, S.H. Kim, Y.K. Kim, N. Kimura, L. Kirsch, S. Klimenko, B. Knuteson, B.R. Ko, S.A. Koay, K. Kondo, D.J. Kong, J. Konigsberg, A. Korytov, A.V. Kotwal, M. Kreps, J. Kroll, D. Krop, N. Krumnack, M. Kruse, V. Krutelyov, T. Kubo, T. Kuhr, N.P. Kulkarni, M. Kurata, Y. Kusakabe, S. Kwang, A.T. Laasanen, S. Lami, S. Lammel, M. Lancaster, R.L. Lander, K. Lannon, A. Lath, G. Latino r , I. Lazzizzera u , T. LeCompte, E. Lee, H.S. Lee, S.W. Lee o , S. Leone, J.D. Lewis, C.S. Lin, J. Linacre, M. Lindgren, E. Lipeles, A. Lister, D.O. Litvintsev, C. Liu, T. Liu, N.S. Lockyer, A. Loginov, M. Loreti u , L. Lovas, R.-S. Lu, D. Lucchesi u , J. Lueck, C. Luci v , P. Lujan, P. Lukens, G. Lungu, L. Lyons, J. Lys, R. Lysak, E. Lytken, P. Mack, D. MacQueen, R. Madrak, K. Maeshima, K. Makhoul, T. Maki, P. Maksimovic, S. Malde, S. Malik, G. Manca y , A. Manousakis-Katsikakis, F. Margaroli, C. Marino, C.P. Marino, A. Martin, V. Martin i , M. Mart´ınez, R. Mart´ınez-Ballar´ın, T. Maruyama, P. Mastrandrea, T. Masubuchi, M.E. Mattson, P. Mazzanti, K.S. McFarland, P. McIntyre, R. McNulty h , A. Mehta, P. Mehtala, A. Menzione, P. Merkel, C. Mesropian, T. Miao, N. Miladinovic, R. Miller, C. Mills, M. Milnik, A. Mitra, G. Mitselmakher, H. Miyake, N. Moggi, C.S. Moon, R. Moore, M.J. Morello q , J. Morlok, P. Movilla Fernandez, J. M¨ulmenst¨adt, A. Mukherjee, Th. Muller, R. Mumford, P. Murat, M. Mussini t , J. Nachtman, Y. Nagai, A. Nagano, J. Naganoma, K. Nakamura, I. Nakano, A. Napier, V. Necula, C. Neu, M.S. Neubauer, J. Nielsen e , L. Nodulman, M. Norman, O. Norniella, E. Nurse, L. Oakes, S.H. Oh, Y.D. Oh, I. Oksuzian, T. Okusawa, R. Orava, K. Osterberg, S. Pagan Griso u , C. Pagliarone, E. Palencia, V. Papadimitriou, A. Papaikonomou, A.A. Paramonov, B. Parks, S. Pashapour, J. Patrick, G. Pauletta w , M. Paulini, C. Paus, D.E. Pellett, A. Penzo, T.J. Phillips, G. Piacentino, E. Pianori, L. Pinera, K. Pitts, C. Plager, L. Pondrom, O. Poukhov ∗ , N. Pounder, F. Prakoshyn, A. Pronko, J. Proudfoot, F. Ptohos g , E. Pueschel, G. Punzi q , J. Pursley, J. Rademacker c , A. Rahaman, V. Ramakrishnan, N. Ranjan, I. Redondo, B. Reisert, V. Rekovic, P. Renton, M. Rescigno, S. Richter, F. Rimondi t , L. Ristori, A. Robson, T. Rodrigo, T. Rodriguez, E. Rogers, S. Rolli, R. Roser, M. Rossi, R. Rossin, P. Roy, A. Ruiz, J. Russ, V. Rusu, H. Saarikko, A. Safonov, W.K. Sakumoto, O. Salt´o, L. Santi w , S. Sarkar v , L. Sartori, K. Sato, A. Savoy-Navarro, T. Scheidle, P. Schlabach, A. Schmidt, E.E. Schmidt, M.A. Schmidt, M.P. Schmidt ∗ , M. Schmitt, T. Schwarz, L. Scodellaro, A.L. Scott, A. Scribano r , F. Scuri, A. Sedov, S. Seidel, Y. Seiya, A. Semenov, L. Sexton-Kennedy, A. Sfyrla, S.Z. Shalhout, T. Shears, P.F. Shepard, D. Sherman, M. Shimojima l , S. Shiraishi, M. Shochet, Y. Shon, I. Shreyber, A. Sidoti, P. Sinervo, A. Sisakyan, A.J. Slaughter, J. Slaunwhite, K. Sliwa, J.R. Smith, F.D. Snider, R. Snihur, A. Soha, S. Somalwar, V. Sorin, J. Spalding, T. Spreitzer, P. Squillacioti r , M. Stanitzki, R. St. Denis, B. Stelzer, O. Stelzer-Chilton, D. Stentz, J. Strologas, D. Stuart, J.S. Suh, A. Sukhanov, I. Suslov, T. Suzuki, A. Taffard d , R. Takashima, Y. Takeuchi, R. Tanaka, M. Tecchio, P.K. Teng, K. Terashi, J. Thom f , A.S. Thompson, G.A. Thompson, E. Thomson, P. Tipton, V. Tiwari, S. Tkaczyk, D. Toback, S. Tokar, K. Tollefson, T. Tomura, D. Tonelli, S. Torre, D. Torretta, P. Totaro w , S. Tourneur, Y. Tu, N. Turini r , F. Ukegawa, S. Vallecorsa, N. van Remortel a , A. Varganov, E. Vataga s , F. V´azquez j , G. Velev, C. Vellidis, V. Veszpremi, M. Vidal, R. Vidal, I. Vila, R. Vilar, T. Vine, M. Vogel, I. Volobouev o , G. Volpi q , F. W¨urthwein, P. Wagner, R.G. Wagner, R.L. Wagner, J. Wagner-Kuhr, W. Wagner, T. Wakisaka, R. Wallny, S.M. Wang, A. Warburton, D. Waters, M. Weinberger, W.C. Wester III, B. Whitehouse, D. Whiteson d , A.B. Wicklund, E. Wicklund, G. Williams, H.H. Williams, P. Wilson, B.L. Winer, P. Wittich f , S. Wolbers, C. Wolfe, T. Wright, X. Wu, S.M. Wynne, S. Xie, A. Yagil, K. Yamamoto, J. Yamaoka, U.K. Yang k , Y.C. Yang, W.M. Yao, G.P. Yeh, J. Yoh, K. Yorita, T. Yoshida, G.B. Yu, I. Yu, S.S. Yu, J.C. Yun, L. Zanello v , A. Zanetti, I. Zaw, X. Zhang, Y. Zheng b , and S. Zucchelli t (CDF Collaboration † ) Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China Argonne National Laboratory, Argonne, Illinois 60439 University of Athens, 157 71 Athens, Greece Institut de Fisica d’Altes Energies, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain Baylor University, Waco, Texas 76798 Istituto Nazionale di Fisica Nucleare Bologna, t University of Bologna, I-40127 Bologna, Italy Brandeis University, Waltham, Massachusetts 02254 University of California, Davis, Davis, California 95616 University of California, Los Angeles, Los Angeles, California 90024 University of California, San Diego, La Jolla, California 92093 University of California, Santa Barbara, Santa Barbara, California 93106 Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain Carnegie Mellon University, Pittsburgh, PA 15213 Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 Comenius University, 842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice, Slovakia Joint Institute for Nuclear Research, RU-141980 Dubna, Russia Duke University, Durham, North Carolina 27708 Fermi National Accelerator Laboratory, Batavia, Illinois 60510 University of Florida, Gainesville, Florida 32611 Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy University of Geneva, CH-1211 Geneva 4, Switzerland Glasgow University, Glasgow G12 8QQ, United Kingdom Harvard University, Cambridge, Massachusetts 02138 Division of High Energy Physics, Department of Physics,University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland University of Illinois, Urbana, Illinois 61801 The Johns Hopkins University, Baltimore, Maryland 21218 Institut f¨ur Experimentelle Kernphysik, Universit¨at Karlsruhe, 76128 Karlsruhe, Germany Center for High Energy Physics: Kyungpook National University,Daegu 702-701, Korea; Seoul National University, Seoul 151-742,Korea; Sungkyunkwan University, Suwon 440-746,Korea; Korea Institute of Science and Technology Information, Daejeon,305-806, Korea; Chonnam National University, Gwangju, 500-757, Korea Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720 University of Liverpool, Liverpool L69 7ZE, United Kingdom University College London, London WC1E 6BT, United Kingdom Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Institute of Particle Physics: McGill University, Montr´eal,Canada H3A 2T8; and University of Toronto, Toronto, Canada M5S 1A7 University of Michigan, Ann Arbor, Michigan 48109 Michigan State University, East Lansing, Michigan 48824 Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia University of New Mexico, Albuquerque, New Mexico 87131 Northwestern University, Evanston, Illinois 60208 The Ohio State University, Columbus, Ohio 43210 Okayama University, Okayama 700-8530, Japan Osaka City University, Osaka 588, Japan University of Oxford, Oxford OX1 3RH, United Kingdom Istituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, u University of Padova, I-35131 Padova, Italy LPNHE, Universite Pierre et Marie Curie/IN2P3-CNRS, UMR7585, Paris, F-75252 France University of Pennsylvania, Philadelphia, Pennsylvania 19104 Istituto Nazionale di Fisica Nucleare Pisa, q University of Pisa, r University of Siena and s Scuola Normale Superiore, I-56127 Pisa, Italy University of Pittsburgh, Pittsburgh, Pennsylvania 15260 Purdue University, West Lafayette, Indiana 47907 University of Rochester, Rochester, New York 14627 The Rockefeller University, New York, New York 10021 Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1, v Sapienza Universit`a di Roma, I-00185 Roma, Italy Rutgers University, Piscataway, New Jersey 08855 Texas A&M University, College Station, Texas 77843 Istituto Nazionale di Fisica Nucleare Trieste/ Udine, w University of Trieste/ Udine, Italy University of Tsukuba, Tsukuba, Ibaraki 305, Japan Tufts University, Medford, Massachusetts 02155 Waseda University, Tokyo 169, Japan Wayne State University, Detroit, Michigan 48201 University of Wisconsin, Madison, Wisconsin 53706 Yale University, New Haven, Connecticut 06520
We present the first direct experimental bound on the total decay width of the top quark, Γ t ,using 955 pb − of the Tevatron’s p ¯ p collisions recorded by the Collider Detector at Fermilab. Weidentify 253 top-antitop pair candidate events. The distribution of reconstructed top quark massfrom these events is fitted to templates representing different values of the top quark width. Usinga confidence interval based on likelihood ratio ordering, we extract an upper limit at 95% C.L. ofΓ t < . /c . PACS numbers: 14.65.Ha, 13.85.Qk, 12.15.Ff ∗ Deceased † With visitors from a Universiteit Antwerpen, B-2610 Antwerp,Belgium, b Chinese Academy of Sciences, Beijing 100864, China, c University of Bristol, Bristol BS8 1TL, United Kingdom, d University of California Irvine, Irvine, CA 92697, e University ofCalifornia Santa Cruz, Santa Cruz, CA 95064, f Cornell Univer-sity, Ithaca, NY 14853, g University of Cyprus, Nicosia CY-1678,Cyprus, h University College Dublin, Dublin 4, Ireland, i University
Due to its large mass, the top quark has the largest de-cay width and hence the shortest lifetime of the quarksin the standard model (SM). The total width of thetop quark at the leading order is dependent on the topquark mass m t and the Fermi coupling constant G F :Γ t = G F m t / (8 π √ W boson and b quark masses( M W , m b ), non-zero off-diagonal elements of the quark-mixing matrix, and higher order corrections in the strongcoupling constant α s . Neglecting terms of order m b /m t , α s , and ( α s /π ) M W /m t , the width predicted in the SMat next-to-leading-order is:Γ t = Γ t (1 − M W m t ) (1 + 2 M W m t )[1 − α s π ( 2 π −
52 )] . The total width of the top quark is calculated to a preci-sion of about 1% in the SM; it is approximately 1 . m t = 175 GeV /c [1, 2].A deviation from the SM prediction could indicate asignificant contribution from top quark decays to non–SM particles such as t → bH + (where H + is the chargedHiggs boson in the supersymmetric model), or from rareSM processes such as t → dW + and t → sW + . Al-though such scenarios have not been observed experimen-tally [3, 4, 5, 6, 7], a general way to rule out the presenceof a large top quark decay rate to non–SM channels, in-cluding those with non-detectable final states, is throughexperimental constraints on Γ t . To date, there have beenno direct experimental measurements of the total widthof the top quark.The data set for the analysis presented in this paperis collected by the CDF II detector, a multipurpose par-ticle detector for p ¯ p collisions at √ s = 1 .
96 TeV at theFermilab Tevatron. A charged particle tracking systemimmersed in a magnetic field consists of a silicon mi-crostrip tracker and a drift chamber. Electromagneticand hadronic calorimeters surround the tracking systemand measure particle energies. Drift chambers and scin-tillators located outside the calorimeters detect muons.The detector is described in detail elsewhere [8].We employ a cylindrical coordinate system where θ and φ are the polar and azimuthal angle, respectively,with respect to the proton beam. Transverse energy and of Edinburgh, Edinburgh EH9 3JZ, United Kingdom, j UniversidadIberoamericana, Mexico D.F., Mexico, k University of Manchester,Manchester M13 9PL, England, l Nagasaki Institute of Applied Sci-ence, Nagasaki, Japan, m University de Oviedo, E-33007 Oviedo,Spain, n Queen Mary, University of London, London, E1 4NS, Eng-land, o Texas Tech University, Lubbock, TX 79409, p IFIC(CSIC-Universitat de Valencia), 46071 Valencia, Spain, x Royal Society ofEdinburgh/Scottish Executive Support Research Fellow, y IstitutoNazionale di Fisica Nucleare, Sezione di Cagliari, 09042 Monserrato(Cagliari), Italy
TABLE I: Event selection requirements for the 1-tag and 2-tag event samples.Event selection category 1-tag 2-tag E eT (GeV) or p µT (GeV /c ) > E T (GeV) > E T (GeV) > E T (GeV) > > b tags 1 ≥ momentum are E T = E sin θ and p T = | p | sin θ , respec-tively, where E and p are energy and momentum. Miss-ing transverse energy, E T , is defined as the magnitude ofthe vector − Σ i E iT n i where E iT is the magnitude of trans-verse energy contained in each calorimeter tower i , and n i is the unit vector from the collision point to the towerin the transverse plane.Top quarks are produced primarily by strong inter-action in top-antitop ( t ¯ t ) pairs at the Tevatron. Topquarks decay almost exclusively to a W boson and a b quark through the weak interaction in the SM. We iden-tify candidate t ¯ t events in the “lepton + jets” channel,where one W boson decays to an electron or a muon,and a neutrino, while the other W boson decays to aquark-antiquark pair. We select events consistent withthis topology, requiring a high- p T electron or muon can-didate, missing transverse energy denoting the presenceof a neutrino, and four jets. Jets are reconstructed usinga cone algorithm with radius ∆R ≡ p ∆ η + ∆ φ = 0 . E T >
15 GeV must be identifiedas a b quark candidate through the presence of a dis-placed vertex within the jet cone arising from the decayof a long-lived bottom hadron ( b -tag). The event selec-tion criteria are listed in Table I. Detailed informationon event selection is available elsewhere [9, 10].We divide the candidate events into two exclusiveclasses: one (1-tag) containing events with one b -taggedjet among the leading four, and another (2-tag) with twoor more such jets. Separating these subsamples results ina more efficient use of statistical information due to theirdifferent reconstructed top mass resolution and signal-to-background ratios. Background events are expectedprimarily from W production in association with jets( W + jets), multijet processes where a jet is misidentifiedas a charged lepton and E T results from energy mismea-surement of the jets (non- W ), and small contributionsfrom electroweak backgrounds (EWK) composed of sin-gle top quark and diboson ( W W , W Z , ZZ ) production.Table II summarizes the expected sample compositionsthat are obtained by scaling to 955 pb − from a previous t ¯ t analysis with 318 pb − [11]. A detailed description ofthe background estimation is given in Ref. [9].After event selection, the analysis proceeds in threesteps. First, we reconstruct a top quark mass m reco t fromeach event using a kinematic fitter. The width of the TABLE II: The sources and expected numbers of backgroundevents, and the number of events observed for the 1-tag and2-tag event samples in our 955 pb − dataset.Background source 1-tag 2-tag W + jets 21.4 ± ± W ± ± ± ± ± ± reconstructed mass distribution for the selected events issensitive to Γ t . The second step is a likelihood fit of thereconstructed mass distributions using simulated signaland background distributions that yields an estimatorof Γ t . Finally, we use a frequentist prescription (withBayesian treatment of systematic uncertainties [12]) todetermine a 95% C.L. upper limit on Γ t in the physicallyallowed region.We perform a χ minimization to fit the momenta ofthe t ¯ t decay products and determine m reco t for each eventusing the four leading jets. We assume that the finalstate arises from the decay of a t ¯ t pair into W bosonsand b quarks. To resolve the ambiguity arising from thedifferent ways of assigning the jets to the four quarks, werequire that b -tagged jets are assigned to b quarks andselect the assignment with the lowest χ . This kinematicfitter is used in other CDF analyses and is described indetail in Ref. [11]. In the χ fit, both sets of W decaydaughters are constrained to have the invariant mass ofthe W boson, and both W b states are constrained to havethe same mass. Although the top and antitop quark willlikely be produced with different masses, we confirmedthat there is no significant difference in the sensitivityresulting from the m t = m ¯ t condition even for a largevalue of Γ t .To distinguish between different values of Γ t , we com-pare the m reco t distribution from our data to a series ofsamples created using the pythia m t = 175 GeV /c and various values of Γ t between0 .
001 GeV and 100 GeV. Although pythia does not fullyaccount for quantum interference with irreducible back-ground diagrams and off-shell effects, for Γ t .
30 GeVthese effects are small, and the existing description isexpected to be adequate [14]. W + jets backgroundevents are generated using alpgen herwig m reco t templates. As an example, Fig. 1 shows templates forthe signal m reco t distribution in the 2-tag subsample atthree values of Γ t . We parameterize the m reco t distribu-tions as a function of Γ t . Small shifts in the mean ofthe templates are induced by the interplay between the ) (GeV/c recot m100 150 200 250 300 F r ac t i on = 175 GeV/c t m /ndf=1.1) c = 1.5 GeV ( inputt G /ndf=1.0) c = 15 GeV ( inputt G /ndf=1.1) c = 30 GeV ( inputt G FIG. 1: The parameterized signal m reco t distributions andgoodness of the parameterization are shown for the 2-tag sub-sample at three different values of Γ t . The parameterizationis determined in a global fit to all the 2-tag templates. Theparameterized signal m reco t distributions for 1-tag are similar. top mass Breit-Wigner distribution and the parton distri-bution functions that preferentially produce events withlow quark masses. In the likelihood fit, we constrain thebackground templates in the 2-tag and 1-tag samples tothe levels given in Table II. The best fit value Γ fit t is thewidth which maximizes the likelihood.We allow negative Γ fit t values that represent m reco t dis-tributions narrower than the nominal due to statisticalfluctuations. The expected m reco t distribution for a neg-ative Γ fit t is derived from an extrapolation of the param-eterization to the unphysical region. The reconstructedtop mass distributions from the data and the results ofthe likelihood fit are shown in Fig. 2. The data are con-sistent with the fitted curves with the preferred value ofΓ fit t = − . fit t about 40% ofthe time and Γ fit t less than − . . t , however, will be constrained to the physicalregion.To set a limit on the true value of Γ t , we employthe Neyman construction [18] to ensure a coverage ofat least 95%. The likelihood-ratio ordering principle dueto Feldman and Cousins [19] provides a smooth transi-tion from one-sided to two-sided limits and usually guar-antees a non-empty interval. We derive the confidencebelts from ensembles of simulated experiments in whichsignal events are selected from the simulated samples gen-erated with different values of Γ t . The Γ fit t distributionfrom each such ensemble is convoluted with a shape thatrepresents the effects of systematic uncertainties as de- ) E ve n t s / ( G e V / c (GeV) fitt G -40 -20 0 20 40 60 80 100 ) m ax - l n ( L / L = -4.8 GeV fitt G ) (GeV/c reco.t m100 150 200 250 300 350 400 ) E ve n t s / ( G e V / c -1 L = 955 pb
Data 1-tag (171 evts)Data 2-tag (82 evts)Signal + BkgdBkgd only
FIG. 2: The m reco t distribution is shown for 1-tag and 2-tagdata samples overlaid with the signal and background distri-butions from the combined fit. A Γ fit t likelihood scan is shownin the inset; for the shaded non-physical region (Γ fit t < m reco t distributions extrapolated from the pa-rameterization to shapes with Γ fit t > scribed below.Since the top quark mass reconstruction is dominatedby the measurement of jet energy, and since our fit islargely determined by the peak and the width of the m reco t distribution, the uncertainties on the jet energy scale andthe jet energy resolution are the dominant uncertaintiesin the top width measurement. The uncertainties on thejet energy scale calibration are extensively studied usinga combination of simulated and data control samples [20]and amount to about 3% of the measured jet energy forjets in the t ¯ t sample. The effect on the Γ fit t distributionis non-linear, with larger Γ fit t being more likely for largerjet energy scale shifts in either direction. This is becausethe only degree of freedom in the templates is the width,and a signal template with a larger Γ t accommodates theevents with the shifted peak.We select events with one jet and one high- p T pho-ton and compare their energies to study the jet energyresolution. Data and pythia events show similar jetresolution of 15% – 10% for jet transverse energies be-tween 20 GeV and 200 GeV, respectively. Taking intoaccount statistical uncertainty of the data, we define a p T -dependent systematic uncertainty on jet resolution of10% – 4% to cover the difference. Then, we add Gaussiansmearing with corresponding uncertainty to each jet in signal Monte Carlo events. We also study smaller system-atic uncertainties in Γ fit t related to the background m reco t shape, Monte Carlo statistics, the Monte Carlo genera-tor, the parton distribution functions, and other signalmodeling effects [11]. The combined convolution shape,accounting for all systematic uncertainties, has a shift of − . . . . t of 1.5 – 30 GeV. Figure 3 shows the 95%confidence belts after including systematic uncertainties.The fitted value from data, Γ fit t = − . t < . /c . The one-dimensional like-lihood is sensitive to this assumption in the same wayas described above for jet energy scale uncertainties. Inparticular, if the top quark mass is consistent with thecurrent world average of 171 . ± . /c [21], the con-fidence belts would shift to higher Γ fit t values, resultingin an upper limit of Γ t lower than what we quoted in thispaper.In summary, using 253 top-antitop pair candidateevents we present the first direct experimental up-per limit on the total decay width of the top quark,Γ t < . m t = 175 GeV /c .This corresponds to a limit on the top quark lifetime of τ t > × − s. This measurement is statistically lim-ited and its dominant systematic uncertainties are likelyreducible with statistics. The precision of this measure-ment, therefore, will continue to improve over the courseof Run II of the Tevatron.We thank Torbj¨orn Sj¨ostrand, Stephen Mrenna, Pe-ter Skands, Alessandro Ballestrero, and Ezio Maina fordiscussions related to the Monte Carlo modeling of thetop quark lineshape. We thank the Fermilab staff andthe technical staffs of the participating institutions fortheir vital contributions. This work was supported bythe U.S. Department of Energy and National ScienceFoundation; the Italian Istituto Nazionale di Fisica Nu-cleare; the Ministry of Education, Culture, Sports, Sci-ence and Technology of Japan; the Natural Sciences andEngineering Research Council of Canada; the NationalScience Council of the Republic of China; the Swiss Na-tional Science Foundation; the A.P. Sloan Foundation;the Bundesministerium f¨ur Bildung und Forschung, Ger-many; the Korean Science and Engineering Foundationand the Korean Research Foundation; the Science andTechnology Facilities Council and the Royal Society, UK;the Institut National de Physique Nucleaire et Physiquedes Particules/CNRS; the Russian Foundation for Ba-sic Research; the Comisi´on Interministerial de Ciencia yTecnolog´ıa, Spain; the European Community’s HumanPotential Programme; the Slovak R&D Agency; and theAcademy of Finland. (GeV) fitt G -20 0 20 40 60 80 100 120 ( G e V ) t G -1 L = 955 pb95% Confidence Level = 175 GeV/c t m FIG. 3: The confidence band in Γ fit t for a 95% C.L. is shown.Results from simulated experiments assuming a 955 pb − dataset at different values of Γ t are convoluted with a smear-ing function to account for systematic uncertainties. The fit-ted value from the data is indicated by an arrow.[1] A. Czarnecki and K. Melnikov, Nucl. Phys. B544 , 520(1999).[2] K. G. Chetyrkin, R. 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