Measurement of W-Boson Polarization in Top-Quark Decay in <em>pp</em> Collisions at √s=1.96  TeV

Article

Reference

Measurement of W-Boson Polarization in Top-Quark Decay in pp Collisions at √s=1.96  TeV

CDF Collaboration

CLARK, Allan Geoffrey (Collab.), et al.

Abstract

We report measurements of the polarization of W bosons from top-quark decays using 2.7 fb−1 of pp collisions collected by the CDF II detector. Assuming a top-quark mass of 175   GeV/c2, three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f0) and right-handed (f+) W bosons yields the model-independent results f0=0.88±0.11(stat)±0.06(syst) and f+=−0.15±0.07(stat)±0.06(syst) with a correlation coefficient of −0.59. A measurement of f0 [f+] constraining f+ [f0] to its standard model value of 0.0 [0.7] yields f0=0.70±0.07(stat)±0.04(syst) [f+=−0.01±0.02(stat)±0.05(syst)]. All these results are consistent with standard model expectations. We achieve the single most precise measurements of f0 for both the model-independent and model-dependent determinations.

CDF Collaboration, CLARK, Allan Geoffrey (Collab.), et al . Measurement of W-Boson

Polarization in Top-Quark Decay in pp Collisions at √s=1.96  TeV. Physical Review Letters , 2010, vol. 105, p. 8p.

DOI : 10.1103/PhysRevLett.105.042002

Available at:

http://archive-ouverte.unige.ch/unige:38694

Disclaimer: layout of this document may differ from the published version.

1 / 1

Measurement of W-Boson Polarization in Top-Quark Decay in p p Collisions at ffiffiffi p s

¼ 1:96 TeV

T. Aaltonen,²⁵J. Adelman,¹⁵B. A´ lvarez Gonza´lez,^13,xS. Amerio,^46,45D. Amidei,³⁶A. Anastassov,⁴⁰A. Annovi,²¹ J. Antos,¹⁶G. Apollinari,¹⁹J. Appel,¹⁹A. Apresyan,⁵⁴T. Arisawa,⁶⁵A. Artikov,¹⁷J. Asaadi,⁶⁰W. Ashmanskas,¹⁹ A. Attal,⁴A. Aurisano,⁶⁰F. Azfar,⁴⁴W. Badgett,¹⁹A. Barbaro-Galtieri,³⁰V. E. Barnes,⁵⁴B. A. Barnett,²⁷P. Barria,^51,49 P. Bartos,¹⁶G. Bauer,³⁴P.-H. Beauchemin,³⁵F. Bedeschi,⁴⁹D. Beecher,³²S. Behari,²⁷G. Bellettini,^50,49J. Bellinger,⁶⁷

D. Benjamin,¹⁸A. Beretvas,¹⁹A. Bhatti,⁵⁶M. Binkley,^19,aD. Bisello,^46,45I. Bizjak,^32,eeR. E. Blair,²C. Blocker,⁸ B. Blumenfeld,²⁷A. Bocci,¹⁸A. Bodek,⁵⁵V. Boisvert,⁵⁵D. Bortoletto,⁵⁴J. Boudreau,⁵³A. Boveia,¹²B. Brau,^12,b A. Bridgeman,²⁶L. Brigliadori,^7,6C. Bromberg,³⁷E. Brubaker,¹⁵J. Budagov,¹⁷H. S. Budd,⁵⁵S. Budd,²⁶K. Burkett,¹⁹ G. Busetto,^46,45P. Bussey,²³A. Buzatu,³⁵K. L. Byrum,²S. Cabrera,^18,zC. Calancha,³³S. Camarda,⁴M. Campanelli,³²

M. Campbell,³⁶F. Canelli,^15,19A. Canepa,⁴⁸B. Carls,²⁶D. Carlsmith,⁶⁷R. Carosi,⁴⁹S. Carrillo,^20,oS. Carron,¹⁹ B. Casal,¹³M. Casarsa,¹⁹A. Castro,^7,6P. Catastini,^51,49D. Cauz,⁶¹V. Cavaliere,^51,49M. Cavalli-Sforza,⁴A. Cerri,³⁰

L. Cerrito,^32,rS. H. Chang,²⁹Y. C. Chen,¹M. Chertok,⁹G. Chiarelli,⁴⁹G. Chlachidze,¹⁹F. Chlebana,¹⁹K. Cho,²⁹ D. Chokheli,¹⁷J. P. Chou,²⁴K. Chung,^19,pW. H. Chung,⁶⁷Y. S. Chung,⁵⁵T. Chwalek,²⁸C. I. Ciobanu,⁴⁷M. A. Ciocci,^51,49 A. Clark,²²D. Clark,⁸G. Compostella,⁴⁵M. E. Convery,¹⁹J. Conway,⁹M. Corbo,⁴⁷M. Cordelli,²¹C. A. Cox,⁹D. J. Cox,⁹ F. Crescioli,^50,49C. Cuenca Almenar,⁶⁸J. Cuevas,^13,xR. Culbertson,¹⁹J. C. Cully,³⁶D. Dagenhart,¹⁹N. d’Ascenzo,^47,w M. Datta,¹⁹T. Davies,²³P. de Barbaro,⁵⁵S. De Cecco,⁵⁷A. Deisher,³⁰G. De Lorenzo,⁴M. Dell’Orso,^50,49C. Deluca,⁴

L. Demortier,⁵⁶J. Deng,^18,gM. Deninno,⁶M. d’Errico,^46,45A. Di Canto,^50,49B. Di Ruzza,⁴⁹J. R. Dittmann,⁵ M. D’Onofrio,⁴S. Donati,^50,49P. Dong,¹⁹T. Dorigo,⁴⁵S. Dube,⁵⁹K. Ebina,⁶⁵A. Elagin,⁶⁰R. Erbacher,⁹D. Errede,²⁶ S. Errede,²⁶N. Ershaidat,^47,ddR. Eusebi,⁶⁰H. C. Fang,³⁰S. Farrington,⁴⁴W. T. Fedorko,¹⁵R. G. Feild,⁶⁸M. Feindt,²⁸ J. P. Fernandez,³³C. Ferrazza,^52,49R. Field,²⁰G. Flanagan,^54,tR. Forrest,⁹M. J. Frank,⁵M. Franklin,²⁴J. C. Freeman,¹⁹ I. Furic,²⁰M. Gallinaro,⁵⁶J. Galyardt,¹⁴F. Garberson,¹²J. E. Garcia,²²A. F. Garfinkel,⁵⁴P. Garosi,^51,49H. Gerberich,²⁶

D. Gerdes,³⁶A. Gessler,²⁸S. Giagu,^62,61V. Giakoumopoulou,³P. Giannetti,⁴⁹K. Gibson,⁵³J. L. Gimmell,⁵⁵ C. M. Ginsburg,¹⁹N. Giokaris,³M. Giordani,^62,61P. Giromini,²¹M. Giunta,⁴⁹G. Giurgiu,²⁷V. Glagolev,¹⁷D. Glenzinski,¹⁹

M. Gold,³⁹N. Goldschmidt,²⁰A. Golossanov,¹⁹G. Gomez,¹³G. Gomez-Ceballos,³⁴M. Goncharov,³⁴O. Gonza´lez,³³ I. Gorelov,³⁹A. T. Goshaw,¹⁸K. Goulianos,⁵⁶A. Gresele,^46,45S. Grinstein,⁴C. Grosso-Pilcher,¹⁵R. C. Group,¹⁹ U. Grundler,²⁶J. Guimaraes da Costa,²⁴Z. Gunay-Unalan,³⁷C. Haber,³⁰S. R. Hahn,¹⁹E. Halkiadakis,⁵⁹B.-Y. Han,⁵⁵

J. Y. Han,⁵⁵F. Happacher,²¹K. Hara,⁶³D. Hare,⁵⁹M. Hare,⁶⁴R. F. Harr,⁶⁶M. Hartz,⁵³K. Hatakeyama,⁵C. Hays,⁴⁴ M. Heck,²⁸J. Heinrich,⁴⁸M. Herndon,⁶⁷J. Heuser,²⁸S. Hewamanage,⁵D. Hidas,⁵⁹C. S. Hill,^12,dD. Hirschbuehl,²⁸ A. Hocker,¹⁹S. Hou,¹M. Houlden,³¹S.-C. Hsu,³⁰R. E. Hughes,⁴¹M. Hurwitz,¹⁵U. Husemann,⁶⁸M. Hussein,³⁷ J. Huston,³⁷J. Incandela,¹²G. Introzzi,⁴⁹M. Iori,^58,57A. Ivanov,^9,qE. James,¹⁹D. Jang,¹⁴B. Jayatilaka,¹⁸E. J. Jeon,²⁹

M. K. Jha,⁶S. Jindariani,¹⁹W. Johnson,⁹M. Jones,⁵⁴K. K. Joo,²⁹S. Y. Jun,¹⁴J. E. Jung,²⁹T. R. Junk,¹⁹T. Kamon,⁶⁰ D. Kar,²⁰P. E. Karchin,⁶⁶Y. Kato,^43,nR. Kephart,¹⁹W. Ketchum,¹⁵J. Keung,⁴⁸V. Khotilovich,⁶⁰B. Kilminster,¹⁹ D. H. Kim,²⁹H. S. Kim,²⁹H. W. Kim,²⁹J. E. Kim,²⁹M. J. Kim,²¹S. B. Kim,²⁹S. H. Kim,⁶³Y. K. Kim,¹⁵N. Kimura,⁶⁵ L. Kirsch,⁸S. Klimenko,²⁰K. Kondo,⁶⁵D. J. Kong,²⁹J. Konigsberg,²⁰A. Korytov,²⁰A. V. Kotwal,¹⁸M. Kreps,²⁸J. Kroll,⁴⁸

D. Krop,¹⁵N. Krumnack,⁵M. Kruse,¹⁸V. Krutelyov,¹²T. Kuhr,²⁸N. P. Kulkarni,⁶⁶M. Kurata,⁶³S. Kwang,¹⁵ A. T. Laasanen,⁵⁴S. Lami,⁴⁹S. Lammel,¹⁹M. Lancaster,³²R. L. Lander,⁹K. Lannon,^41,vA. Lath,⁵⁹G. Latino,^51,49 I. Lazzizzera,^46,45T. LeCompte,²E. Lee,⁶⁰H. S. Lee,¹⁵J. S. Lee,²⁹S. W. Lee,^60,yS. Leone,⁴⁹J. D. Lewis,¹⁹C.-J. Lin,³⁰ J. Linacre,⁴⁴M. Lindgren,¹⁹E. Lipeles,⁴⁸A. Lister,²²D. O. Litvintsev,¹⁹C. Liu,⁵³T. Liu,¹⁹N. S. Lockyer,⁴⁸A. Loginov,⁶⁸ L. Lovas,¹⁶D. Lucchesi,^46,45J. Lueck,²⁸P. Lujan,³⁰P. Lukens,¹⁹G. Lungu,⁵⁶J. Lys,³⁰R. Lysak,¹⁶D. MacQueen,³⁵

R. Madrak,¹⁹K. Maeshima,¹⁹K. Makhoul,³⁴P. Maksimovic,²⁷S. Malde,⁴⁴S. Malik,³²G. Manca,^31,f A. Manousakis-Katsikakis,³F. Margaroli,⁵⁴C. Marino,²⁸C. P. Marino,²⁶A. Martin,⁶⁸V. Martin,^23,lM. Martı´nez,⁴ R. Martı´nez-Balları´n,³³P. Mastrandrea,⁵⁷M. Mathis,²⁷M. E. Mattson,⁶⁶P. Mazzanti,⁶K. S. McFarland,⁵⁵P. McIntyre,⁶⁰

R. McNulty,^31,kA. Mehta,³¹P. Mehtala,²⁵A. Menzione,⁴⁹C. Mesropian,⁵⁶T. Miao,¹⁹D. Mietlicki,³⁶N. Miladinovic,⁸ R. Miller,³⁷C. Mills,²⁴M. Milnik,²⁸A. Mitra,¹G. Mitselmakher,²⁰H. Miyake,⁶³S. Moed,²⁴N. Moggi,⁶ M. N. Mondragon,^19,oC. S. Moon,²⁹R. Moore,¹⁹M. J. Morello,⁴⁹J. Morlock,²⁸P. Movilla Fernandez,¹⁹J. Mu¨lmensta¨dt,³⁰

A. Mukherjee,¹⁹Th. Muller,²⁸P. Murat,¹⁹M. Mussini,^7,6J. Nachtman,^19,pY. Nagai,⁶³J. Naganoma,⁶³K. Nakamura,⁶³ I. Nakano,⁴²A. Napier,⁶⁴J. Nett,⁶⁷C. Neu,^48,bbM. S. Neubauer,²⁶S. Neubauer,²⁸J. Nielsen,^30,hL. Nodulman,² M. Norman,¹¹O. Norniella,²⁶E. Nurse,³²L. Oakes,⁴⁴S. H. Oh,¹⁸Y. D. Oh,²⁹I. Oksuzian,²⁰T. Okusawa,⁴³R. Orava,²⁵

K. Osterberg,²⁵S. Pagan Griso,^46,45C. Pagliarone,⁶¹E. Palencia,¹⁹V. Papadimitriou,¹⁹A. Papaikonomou,²⁸ PRL105,042002 (2010) P H Y S I C A L R E V I E W L E T T E R S 23 JULY 2010

A. A. Paramanov,²B. Parks,⁴¹S. Pashapour,³⁵J. Patrick,¹⁹G. Pauletta,^62,61M. Paulini,¹⁴C. Paus,³⁴T. Peiffer,²⁸ D. E. Pellett,⁹A. Penzo,⁶¹T. J. Phillips,¹⁸G. Piacentino,⁴⁹E. Pianori,⁴⁸L. Pinera,²⁰K. Pitts,²⁶C. Plager,¹⁰L. Pondrom,⁶⁷ K. Potamianos,⁵⁴O. Poukhov,^17,aF. Prokoshin,^17,aaA. Pronko,¹⁹F. Ptohos,^19,jE. Pueschel,¹⁴G. Punzi,^50,49J. Pursley,⁶⁷ J. Rademacker,^44,dA. Rahaman,⁵³V. Ramakrishnan,⁶⁷N. Ranjan,⁵⁴I. Redondo,³³P. Renton,⁴⁴M. Renz,²⁸M. Rescigno,⁵⁷ S. Richter,²⁸F. Rimondi,^7,6L. Ristori,⁴⁹A. Robson,²³T. Rodrigo,¹³T. Rodriguez,⁴⁸E. Rogers,²⁶S. Rolli,⁶⁴R. Roser,¹⁹

M. Rossi,⁶¹R. Rossin,¹²P. Roy,³⁵A. Ruiz,¹³J. Russ,¹⁴V. Rusu,¹⁹B. Rutherford,¹⁹H. Saarikko,²⁵A. Safonov,⁶⁰ W. K. Sakumoto,⁵⁵L. Santi,^62,61L. Sartori,⁴⁹K. Sato,⁶³V. Saveliev,^47,wA. Savoy-Navarro,⁴⁷P. Schlabach,¹⁹A. Schmidt,²⁸

E. E. Schmidt,¹⁹M. A. Schmidt,¹⁵M. P. Schmidt,^68,aM. Schmitt,⁴⁰T. Schwarz,⁹L. Scodellaro,¹³A. Scribano,^51,49 F. Scuri,⁴⁹A. Sedov,⁵⁴S. Seidel,³⁹Y. Seiya,⁴³A. Semenov,¹⁷L. Sexton-Kennedy,¹⁹F. Sforza,^50,49A. Sfyrla,²⁶ S. Z. Shalhout,⁶⁶T. Shears,³¹P. F. Shepard,⁵³M. Shimojima,^63,uS. Shiraishi,¹⁵M. Shochet,¹⁵Y. Shon,⁶⁷I. Shreyber,³⁸ A. Simonenko,¹⁷P. Sinervo,³⁵A. Sisakyan,¹⁷A. J. Slaughter,¹⁹J. Slaunwhite,⁴¹K. Sliwa,⁶⁴J. R. Smith,⁹F. D. Snider,¹⁹

R. Snihur,³⁵A. Soha,¹⁹S. Somalwar,⁵⁹V. Sorin,⁴P. Squillacioti,^51,49M. Stanitzki,⁶⁸R. St. Denis,²³B. Stelzer,³⁵ O. Stelzer-Chilton,³⁵D. Stentz,⁴⁰J. Strologas,³⁹G. L. Strycker,³⁶J. S. Suh,²⁹A. Sukhanov,²⁰I. Suslov,¹⁷A. Taffard,^26,g

R. Takashima,⁴²Y. Takeuchi,⁶³R. Tanaka,⁴²J. Tang,¹⁵M. Tecchio,³⁶P. K. Teng,¹J. Thom,^19,iJ. Thome,¹⁴ G. A. Thompson,²⁶E. Thomson,⁴⁸P. Tipton,⁶⁸P. Ttito-Guzma´n,³³S. Tkaczyk,¹⁹D. Toback,⁶⁰S. Tokar,¹⁶K. Tollefson,³⁷

T. Tomura,⁶³D. Tonelli,¹⁹S. Torre,²¹D. Torretta,¹⁹P. Totaro,^62,61M. Trovato,^52,49S.-Y. Tsai,¹Y. Tu,⁴⁸N. Turini,^51,49 F. Ukegawa,⁶³S. Uozumi,²⁹N. van Remortel,^25,cA. Varganov,³⁶E. Vataga,^52,49F. Va´zquez,^20,oG. Velev,¹⁹C. Vellidis,³ M. Vidal,³³I. Vila,¹³R. Vilar,¹³M. Vogel,³⁹I. Volobouev,^30,yG. Volpi,^50,49P. Wagner,⁴⁸R. G. Wagner,²R. L. Wagner,¹⁹

W. Wagner,^28,ccJ. Wagner-Kuhr,²⁸T. Wakisaka,⁴³R. Wallny,¹⁰S. M. Wang,¹A. Warburton,³⁵D. Waters,³² M. Weinberger,⁶⁰J. Weinelt,²⁸W. C. Wester III,¹⁹B. Whitehouse,⁶⁴D. Whiteson,^48,gA. B. Wicklund,²E. Wicklund,¹⁹

S. Wilbur,¹⁵G. Williams,³⁵H. H. Williams,⁴⁸P. Wilson,¹⁹B. L. Winer,⁴¹P. Wittich,^19,iS. Wolbers,¹⁹C. Wolfe,¹⁵ H. Wolfe,⁴¹T. Wright,³⁶X. Wu,²²F. Wu¨rthwein,¹¹A. Yagil,¹¹K. Yamamoto,⁴³J. Yamaoka,¹⁸U. K. Yang,^15,sY. C. Yang,²⁹

W. M. Yao,³⁰G. P. Yeh,¹⁹K. Yi,^19,pJ. Yoh,¹⁹K. Yorita,⁶⁵T. Yoshida,^43,mG. B. Yu,¹⁸I. Yu,²⁹S. S. Yu,¹⁹J. C. Yun,¹⁹ A. Zanetti,⁶¹Y. Zeng,¹⁸X. Zhang,²⁶Y. Zheng,^10,eand S. Zucchelli^7,6

(CDF Collaboration)

1Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China

2Argonne National Laboratory, Argonne, Illinois 60439, USA

3University of Athens, 157 71 Athens, Greece

4Institut de Fisica d’Altes Energies, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain

5Baylor University, Waco, Texas 76798, USA

6Istituto Nazionale di Fisica Nucleare Bologna, I-40127 Bologna, Italy

7University of Bologna, I-40127 Bologna, Italy

8Brandeis University, Waltham, Massachusetts 02254, USA

9University of California, Davis, Davis, California 95616, USA

10University of California, Los Angeles, Los Angeles, California 90024, USA

11University of California, San Diego, La Jolla, California 92093, USA

12University of California, Santa Barbara, Santa Barbara, California 93106, USA

13Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain

14Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA

15Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA

16Comenius University, 842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice, Slovakia

17Joint Institute for Nuclear Research, RU-141980 Dubna, Russia

18Duke University, Durham, North Carolina 27708, USA

19Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA

20University of Florida, Gainesville, Florida 32611, USA

21Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy

22University of Geneva, CH-1211 Geneva 4, Switzerland

23Glasgow University, Glasgow G12 8QQ, United Kingdom

24Harvard University, Cambridge, Massachusetts 02138, USA

25Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland

26University of Illinois, Urbana, Illinois 61801, USA

27The Johns Hopkins University, Baltimore, Maryland 21218, USA

28Institut fu¨r Experimentelle Kernphysik, Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany

042002-2

29Center 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;

Chonbuk National University, Jeonju 561-756, Korea

30Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

31University of Liverpool, Liverpool L69 7ZE, United Kingdom

32University College London, London WC1E 6BT, United Kingdom

33Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain

34Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

35Institute of Particle Physics: McGill University, Montre´al, Que´bec, Canada H3A 2T8;

Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6;

University of Toronto, Toronto, Ontario, Canada M5S 1A7;

and TRIUMF, Vancouver, British Columbia, Canada V6T 2A3

36University of Michigan, Ann Arbor, Michigan 48109, USA

37Michigan State University, East Lansing, Michigan 48824, USA

38Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia

39University of New Mexico, Albuquerque, New Mexico 87131, USA

40Northwestern University, Evanston, Illinois 60208, USA

41The Ohio State University, Columbus, Ohio 43210, USA

42Okayama University, Okayama 700-8530, Japan

43Osaka City University, Osaka 588, Japan

44University of Oxford, Oxford OX1 3RH, United Kingdom

45Istituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova, Italy

46University of Padova, I-35131 Padova, Italy

47LPNHE, Universite Pierre et Marie Curie/IN2P3-CNRS, UMR7585, Paris, F-75252 France

48University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA

49Istituto Nazionale di Fisica Nucleare Pisa, I-56127 Pisa, Italy

50University of Pisa, I-56127 Pisa, Italy

51University of Siena, I-56127 Pisa, Italy

52Scuola Normale Superiore, I-56127 Pisa, Italy

53University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA

54Purdue University, West Lafayette, Indiana 47907, USA

55University of Rochester, Rochester, New York 14627, USA

56The Rockefeller University, New York, New York 10021, USA

57Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1, I-00185 Roma, Italy

58Sapienza Universita` di Roma, I-00185 Roma, Italy

59Rutgers University, Piscataway, New Jersey 08855, USA

60Texas A&M University, College Station, Texas 77843, USA

61Istituto Nazionale di Fisica Nucleare Trieste/Udine, I-34100 Trieste, I-33100 Udine, Italy

62University of Trieste/Udine, I-33100 Udine, Italy

63University of Tsukuba, Tsukuba, Ibaraki 305, Japan

64Tufts University, Medford, Massachusetts 02155, USA

65Waseda University, Tokyo 169, Japan

66Wayne State University, Detroit, Michigan 48201, USA

67University of Wisconsin, Madison, Wisconsin 53706, USA

68Yale University, New Haven, Connecticut 06520, USA (Received 2 March 2010; published 23 July 2010)

We report measurements of the polarization ofWbosons from top-quark decays using 2.7fb¹ofpp collisions collected by the CDF II detector. Assuming a top-quark mass of175 GeV=c², three measure- ments are performed. A simultaneous measurement of the fraction of longitudinal (f₀) and right-handed (f_þ) W bosons yields the model-independent results f₀¼0:880:11ðstatÞ 0:06ðsystÞ and f_þ¼ 0:150:07ðstatÞ 0:06ðsystÞ with a correlation coefficient of 0:59. A measurement of f₀ [f_þ] constrainingf_þ [f₀] to its standard model value of 0.0 [0.7] yieldsf₀¼0:700:07ðstatÞ 0:04ðsystÞ [f_þ¼ 0:010:02ðstatÞ 0:05ðsystÞ]. All these results are consistent with standard model expecta- tions. We achieve the single most precise measurements off₀for both the model-independent and model- dependent determinations.

DOI:10.1103/PhysRevLett.105.042002 PACS numbers: 14.65.Ha, 13.85.Ni, 13.85.Qk, 14.70.Fm

PRL105,042002 (2010) P H Y S I C A L R E V I E W L E T T E R S 23 JULY 2010

The top quark is the most massive fundamental particle observed by experiment [1]. Because of its large mass, in the standard model (SM) the top quark decays before forming a bound state via the charged current weak inter- action into aW^þboson and abquark [2], with a branching fraction above 99% [3]. This provides a unique opportunity to study the properties of a ‘‘bare’’ quark. In particular, the V-A structure of the weak interaction can be tested by reconstructing the polarization of the W^þ boson from top-quark decay. In the SM at tree level [4], theW^þboson is expected to have longitudinal polarizationf₀ ¼0:703, left-handed polarizationf ¼0:297, and right-handed po- larization f_þ ¼3:610⁴ for a top-quark mass m_t¼ 175 GeV=c², a W-boson mass M_W ¼80:413 GeV=c² [5], and a b-quark mass m_b¼4:79 GeV=c² [3]. In the limit ofm_b!0,f₀ ¼m²_t=ð2m²_W þm²_tÞandf_þ¼0. The higher-order QCD and electroweak radiative corrections modify these predictions at the 1%–2% (relative) level [6].

In beyond-the-SM scenarios, significant deviations from the SM expectation are possible due to the presence of anomalous couplings [4] in thetWbvertex. Measurements of W-boson polarization and single top-quark production together set constraints on the anomalous coupling vector and tensor form factors [7].

In this Letter, we measure the polarization of the W boson from top-quark decay. We assume thettproduction mechanism is in agreement with the SM, and we study a data sample enriched in tt!W^þbWb!‘bqq⁰b events where one of the W bosons decays hadronically and the other leptonically (lepton plus jets). We apply a likelihood technique based on the theoretical matrix ele- ments for both the dominant signal process,qq !tt, and the main background process, inclusive production ofWþ jets. This technique was first developed for the measure- ments of top-quark mass andf₀, constrainingf_þto its SM value [8], and utilizes the kinematic and topological infor- mation from the event through integrations over poorly known parton-level quantities. We express the matrix ele- ment in terms of the W-boson polarization fractions and the cosine of the angle between the momentum of the charged lepton or down-type quark in the W-boson rest frame and the momentum of theWboson in the top-quark rest frame. Therefore we extract information on the W-boson polarization from both the leptonic and hadronic W-boson decays. Previous CDF measurements [9,10] used only information from the leptonic decay. While the infor- mation from the hadronic W-boson decay carries a sign ambiguity in cos since we are unable to identify the down-type quark jet its inclusion still improves the sensi- tivity to thef₀polarization fraction. The analysis described in this Letter improves the statistical sensitivity onf₀ by 20% relative to the best previous CDF measurement [9] for the same event sample. The latest D0 measurement also utilizes information from both the leptonic and hadronic W-boson decays [11].

We report measurements of the W-boson polarization for three different hypotheses of top-quark decay:

(i) model-independent with simultaneous measurement of f₀andf_þ; (ii) anomalous tensor couplings with measure- ment of f₀ for fixed f_þ¼0; and (iii) anomalous right- handed couplings with measurement off_þfor fixedf₀ ¼ 0:70.

The polarization fractions are determined using an un- binned likelihood functionLmaximized with respect tof₀, f_þ, and the fraction of events consistent with thettsignal hypothesis,C_s,

Lðf₀; f_þ; C_sÞ ¼Y^N

i¼1

C_s P_sðx;f₀; f_þÞ

hA_sðx;f₀; f_þÞiþ ð1C_sÞ P_bðxÞ

hA_bðxÞi :

Here, N is the number of observed events, x is a set of observed variables, andhA_siandhA_birefer to the average acceptances for tt and Wþjets background events, re- spectively. The dependence of thettsignal acceptance on the polarization fractions is accounted for in hA_si. The signal probabilityP_s and background probabilityP_b den- sities are constructed as in [12] by integrating over the appropriate parton-level differential cross section con- volved with the proton parton distribution functions (PDFs). The parton four momenta are estimated from the single lepton and the four highest transverse energy E_T [13] jets in the event, and transfer functions derived from Monte Carlo (MC) are used to unfold the detector resolu- tion effects. There is an ambiguity in the jet-parton assign- ments and all permutations are used for each event.

The signal differential cross section uses the leading- order matrix element of the qq !tt process [14], ex- pressed in terms ofcosand the polarization fractions:

jMj²¼g⁴_s

9 F_‘F_hð2²sin²_qtÞ;

whereg_sis the strong coupling constant,_qtdescribes the angle between the incoming parton and the top quark in the rest frame of the incoming partons, andis the velocity of the top quarks in the same rest frame. The factorsF_‘ and F_h correspond to the top quarks with a leptonic and a hadronicW-boson decay, such that

F_‘¼2g⁴_Wm²_‘

3m_tt ð2E²_b þ3E_bm_‘ þm²_bÞ3

8ð1þcosÞ²f_þ þ3

4ð1cos²Þf₀þ3

8ð1cosÞ²ð1f₀f_þÞ :

Hereg_Wis the weak coupling constant,m_‘ is the invariant mass of the lepton and neutrino,tis the width of the top quark, m_t andm_b are the masses of the top quark andb quark, respectively, and E_b¼^m2tm_2m^2b_‘^m2‘ . The hadronic factor F_h is similar, with the exception that we do not 042002-4

distinguish between up-type and down-type quarks from W-boson decay and use the averageF_h related to the two permutations. The background differential cross section uses the sum of matrix elements for Wþjets from the

VECBOS[15] MC generator.

The measurement is based on a data set with an inte- grated luminosity of 2:7 fb¹ acquired by the collider detector at Fermilab (CDF II) [16] fromffiffiffis ppcollisions at p ¼1:96 TeV. The data used are collected using high- transverse momentum (p_T) [13] central (pseudorapidity [13] jj<1:1) electron and muon triggers, a high-p_T forward (1:2<jj<2:0) electron trigger, and a trigger that requires large missing transverse energyE6 T [13] with either an energetic electromagnetic cluster or two sepa- rated jets (E6 Tþjets) [17]. TheE6 T þjets trigger is used to select additional events with high-p_Tmuons, which are not selected by the lepton triggers.

Candidate events for the lepton plus jets final state are selected to have a single, isolated electron or muon candi- date with E_T>20 GeV, large E6 T in the event (E6 T >

20 GeV) as expected from the undetectable neutrino, and at least four jets withE_T>20 GeV. Jets are reconstructed using a cone algorithm with radius R¼0:4 in space, and their energies are corrected for nonuniformities in the calorimeter response as a function of jet, multiple pp interactions, and the hadronic jet energy scale of the calorimeter [18]. Of these jets, we require at least one to have originated from abquark by using an algorithm that identifies a long-livedbhadron through the presence of a displaced vertex (btag) [19]. Backgrounds to thettsignal arise from multijet QCD production (QCD), W-boson production in association with jets (Wþjets), and electro- weak backgrounds (EWK) composed of diboson (WW, WZ, ZZ) and single top-quark production. The Wþjets background includes b-flavor jets as well as light flavor jets incorrectly identified asbjets.

A detailed description of the background estimation can be found in Ref. [20]. TableIshows the expected sample composition assuming att cross section of 6.7 pb. There are overlapping events between those collected by the high-p_T lepton triggers and the E6 Tþjets trigger which are included in the centrale=and forwardecategories, and are eliminated from theE6 T þjets category.

TheHERWIG[21] MC generator is used to model thett signal events with m_t¼175 GeV=c². For estimation of various systematic uncertainties and background modeling MC samples are created using thePYTHIA[22] generator, and ALPGEN [23] or MADEVENT [24] with PYTHIA or

HERWIG supplying the parton shower and fragmentation.

The QCD background is modeled using data control samples. The signal and background modeling has been extensively checked. Figure1compares the observed data and the MC-predicted distributions of different kinematic variables. We have validated the background model by studying a high-statistics control sample ofWþjets can-

didates extracted by vetoing events containing b-tagged jets.

We calibrate the results of the likelihood fit using the simulated tt and background samples, and the sample composition of TableI. For the simultaneous measurement off₀andf_þ, we find our estimatef_0;mis related to the true value of f₀ by f_0;m¼ ð0:880:02Þf₀þ ð0:120:01Þ and our estimate off_þ;m is related to the true value off_þ and f₀ by f_þ;m ¼ ð1:260:01Þf_þþ ð0:170:02Þf₀þ ð0:060:01Þ. We use these calibration functions and the measured polarization fractions to extract the true polar- ization fractions. For our measurement off₀withf_þ¼0, we find our estimate f_0;m¼ ð1:150:04Þf₀þ ð0:09 0:02Þ, and for our measurement of f_þ with f₀ ¼0:7, we TABLE I. Number of expected and observed events in 2:7 fb¹assuming attcross section of 6.7 pb.

Process Central Forward E6 Tþjets

e, e

tt 47866 588 13419

Wþjets 9423 1811 256

EWK 1710 31 53

QCD 2822 4637 11

Total expected 61674 12540 16520

Observed 650 136 178

(GeV/c) Leading Jet PT

0 100 200 300 400

Events

0 100

200 data (2.7 fb^-1)

=0.00

=0.70, f+

t f0

t

=0.00

=0.88, f+

t f0

t

=0.30

=0.70, f+

t f0

t Background

(a)

(GeV/c) Lepton PT

0 100 200 300

Events

0 100 200

(b)

2) Di-jet Mass (GeV/c

0 100 200 300

Events

0 50 100 150

(c)

(Leptonic W) θ*

cos

-1 -0.5 0 0.5 1

Events

20 40 60

(d)

FIG. 1. Comparison of four kinematic variables for data and simulation for different W polarization fractions: solid, dashed and dotted histograms correspond to (f₀,f_þ) values of (0.7, 0.0), (0.88,0.0), and (0.7, 0.3), respectively. Plotted are (a) leading jet p_T, (b) lepton p_T; and for the reconstruction chosen as most likely by the per-event likelihood (c) the invariant mass of the pair of light quark jets from the hadronically decayingWboson and (d) thecos of the leptonically decayingW boson.

PRL105,042002 (2010) P H Y S I C A L R E V I E W L E T T E R S 23 JULY 2010

find our estimate f_þ;m¼ ð1:170:05Þf_þþ ð0:01 0:01Þ. The uncertainties on the coefficients of the calibra- tion functions are included in the method-related system- atic uncertainties, which cover possible biases due to the calibration procedure. The differences between our mea- sured values and the true values arise because the signal and background probabilities used in the likelihood do not accurately model the effects of extra jets arising from initial and final state radiation (ISR/FSR) nor the full set of contributing background processes. Even though like- lihood can be calculated only for the physical values off₀ andf_þ, after calibration the corrected measured values can be slightly outside their physical ranges.

The robustness of the fitting procedure over all physical values of (f₀,f_þ) has been tested with simulated experi- ments, using the number of observed data events and the sample composition of TableI. In all cases, the method is unbiased. Near the physical boundaries, we find that the statistical uncertainty is underestimated by as much as a factor of 1.5. We apply a correction to the statistical uncertainty in these regions. Assuming the SM, the ex- pected statistical uncertainties after all corrections for the simultaneous measurement are0:116and0:074forf₀ andf_þ, respectively.

Various sources of systematic uncertainty affecting the measurement are summarized in Table II. The leading sources of systematic uncertainty arise from MC modeling of initial and final state radiation (ISR and FSR), choice of PDFs, choice of parton shower model, uncertainties on the measured jet energy, and the background shape and nor- malization. The method-related uncertainty includes prop- agating the uncertainty on the fit parameters of the calibration functions, including their correlations. All sys- tematic uncertainties are determined by performing simu- lated experiments in which the systematic parameter in question is varied, the default method and calibrations are applied, and the shifts in the mean measured polarization fractions are used to quantify the uncertainty. All shifts are evaluated at the SM helicity fraction.

For the simultaneous measurement of f₀ and f_þ, we exclude the events from the forward electron trigger as this significantly reduces the systematic uncertainty from the background model. With 828 events and after all correc-

tions, we measure

f₀¼0:8790:106ðstatÞ 0:062ðsystÞ; f_þ¼ 0:1510:067ðstatÞ 0:057ðsystÞ:

The statistical correlation between f₀ and f_þ is ¼ 0:59. We estimate a shift of ð0:0100:005Þ in f₀ and ð0:0170:003Þ in f_þ per 1 GeV=c² shift in the top-quark mass from the central value of175 GeV=c². As the central value is unphysical we have elected to ensure coverage by applying the Feldman-Cousins method [25] to obtain the confidence level (C.L.) intervals shown in Fig.2.

Fixing f_þ¼0and with 964 events, we measure after all corrections f₀ ¼0:7010:069ðstatÞ 0:041ðsystÞ. Fixing f₀ ¼0:70, we measure after all correctionsf_þ¼ 0:0100:019ðstatÞ 0:049ðsystÞand findf_þ<0:12at 95% C.L. We estimate a shift ofð0:0110:003Þ inf₀ and ð0:0130:002Þ in f_þ per 1 GeV=c² shift in the top-quark mass from the central value of175 GeV=c².

In summary, we have measured the polarization of theW boson in top-quark decays using a matrix-element method in2:7 fb¹of CDF II data. Our results are consistent with the SM. This result improves the combined statistical and systematic precision on both the model-independent and model-dependent determinations of the longitudinal polar- izationf₀by a factor of 1.3 compared to the best previous measurement [9] for a 1.4 times increase in luminosity, and are the most precise measurements to date.

We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions.

TABLE II. Summary of systematic uncertainties.

Source f₀ f_þ f₀ f_þ

simultaneous

ISR or FSR 0.020 0.018 0.020 0.021

PDF 0.024 0.013 0.009 0.016

JES 0.018 0.017 0.004 0.012

Parton shower 0.012 0.008 0.031 0.017

Background 0.009 0.038 0.042 0.039

Method-related 0.010 0.005 0.024 0.024

Total 0.041 0.048 0.062 0.057

f

0 0.5 1

+

f

0 0.5

1 68% C.L.

90% C.L.

FIG. 2 (color online). Contours in the (f₀,f_þ) plane indicating 68% and 90% C.L. intervals determined using the Feldman- Cousins method. Note that the coverage is correct although the center of the contours is not at the measured value obtained after calibration.

042002-6

This work was supported by the U.S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Founda- tion; the A. P. Sloan Foundation; the Bundesministerium fu¨r Bildung und Forschung, Germany; the World Class University Program, the National Research Foundation of Korea; 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 Ministerio de Ciencia e Innovacio´n, and Programa Consolider-Ingenio 2010, Spain; the Slovak R&D Agency; and the Academy of Finland.

aDeceased.

bWith visitors from University of Massachusetts Amherst, Amherst, MA 01003, USA.

cWith visitors from Universiteit Antwerpen, B-2610 Antwerp, Belgium.

dWith visitors from University of Bristol, Bristol BS8 1TL, United Kingdom.

eWith visitors from Chinese Academy of Sciences, Beijing 100864, China.

fWith visitors from Istituto Nazionale di Fisica Nucleare, Sezione di Cagliari, 09042 Monserrato (Cagliari), Italy.

gWith visitors from University of California Irvine, Irvine, CA 92697, USA.

hWith visitors from University of California Santa Cruz, Santa Cruz, CA 95064, USA.

iWith visitors from Cornell University, Ithaca, NY 14853, USA.

jWith visitors from University of Cyprus, Nicosia CY- 1678, Cyprus.

kWith visitors from University College Dublin, Dublin 4, Ireland.

lWith visitors from University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.

mWith visitors from University of Fukui, Fukui City, Fukui Prefecture, Japan 910-0017.

nWith visitors from Kinki University, Higashi-Osaka City, Japan 577-8502.

oWith visitors from Universidad Iberoamericana, Mexico D.F., Mexico.

pWith visitors from University of Iowa, Iowa City, IA 52242, USA.

qWith visitors from Kansas State University, Manhattan, KS 66506, USA.

rWith visitors from Queen Mary, University of London, London, E1 4NS, United Kingdom.

sWith visitors from University of Manchester, Manchester M13 9PL, United Kingdom.

tWith visitors from Muons, Inc., Batavia, IL 60510, USA.

uWith visitors from Nagasaki Institute of Applied Science, Nagasaki, Japan.

vWith visitors from University of Notre Dame, Notre Dame, IN 46556, USA.

wWith visitors from Obninsk State University, Obninsk, Russia.

xWith visitors from University de Oviedo, E-33007 Oviedo, Spain.

yWith visitors from Texas Tech University, Lubbock, TX 79609, USA.

zWith visitors from IFIC(CSIC-Universitat de Valencia), 56071 Valencia, Spain.

aaWith visitors from Universidad Tecnica Federico Santa Maria, 110v Valparaiso, Chile.

bbWith visitors from University of Virginia, Charlottesville, VA 22906, USA.

ccWith visitors from Bergische Universita¨t Wuppertal, 42097 Wuppertal, Germany.

ddWith visitors from Yarmouk University, Irbid 211-63, Jordan.

eeOn leave from J. Stefan Institute, Ljubljana, Slovenia.

[1] F. Abe et al. (CDF Collaboration), Phys. Rev. Lett.74, 2626 (1995); S. Abachiet al.(D0 Collaboration), Phys.

Rev. Lett.74, 2632 (1995).

[2] Charge-conjugate modes are included implicitly through- out this Letter.

[3] C. Amsler et al. (Particle Data Group), Phys. Lett. B 667, 1 (2008) and 2009 partial update for the 2010 edition.

[4] J. Aguilar-Saavedra et al., Eur. Phys. J. C 50, 519 (2007).

[5] T. Aaltonenet al.(CDF Collaboration), Phys. Rev. Lett.

99, 151801 (2007).

[6] M. Fischeret al.,Phys. Rev. D63, 031501(R) (2001); H. S.

Doet al.,Phys. Rev. D67, 091501(R) (2003).

[7] V. M. Abazovet al.(D0 Collaboration),Phys. Rev. Lett.

102, 092002 (2009).

[8] V. M. Abazovet al.(D0 Collaboration),Nature (London) 429, 638 (2004); V. M. Abazovet al.(D0 Collaboration), Phys. Lett. B617, 1 (2005).

[9] T. Aaltonenet al.(CDF Collaboration),Phys. Lett. B674, 160 (2009).

[10] A. Abulenciaet al.(CDF Collaboration),Phys. Rev. Lett.

98, 072001 (2007); A. Abulencia et al. (CDF Collaboration), Phys. Rev. D 75, 052001 (2007); A.

Abulenciaet al. (CDF Collaboration),Phys. Rev. D73, 111103 (2006); D. Acosta et al. (CDF Collaboration), Phys. Rev. D71, 031101 (2005).

[11] V. M. Abazovet al.(D0 Collaboration),Phys. Rev. Lett.

100, 062004 (2008).

[12] A. Abulenciaet al.(CDF Collaboration),Phys. Rev. Lett.

99, 182002 (2007).

[13] We use a cylindrical coordinate system where thezaxis is along the proton beam direction andis the polar angle.

Pseudorapidity is¼ lntanð=2Þ, while transverse mo- mentum isp_T¼ jpjsin, and transverse energy isE_T¼ Esin. Missing transverse energy, E6 T, is defined as the magnitude ofP

iEⁱ_Tn^_i, wheren^_iis the unit vector in the PRL105,042002 (2010) P H Y S I C A L R E V I E W L E T T E R S 23 JULY 2010

azimuthal plane that points from the beam line to theith calorimeter tower.

[14] G. Mahlon and S. Parke,Phys. Lett. B411, 173 (1997);

G. Mahlon and S. Parke,Phys. Rev. D53, 4886 (1996).

[15] F. A. Berends, W. T. Giele, and H. Kuijf, Nucl. Phys. B 321, 39 (1989).

[16] D. Acosta et al.(CDF Collaboration), Phys. Rev. D 71, 031101(R) (2005).

[17] A. Abulenciaet al.(CDF Collaboration),Phys. Rev. D74, 072006 (2006); T. Aaltonen et al.(CDF Collaboration), Phys. Rev. Lett.100, 211801 (2008).

[18] A. Bhattiet al.,Nucl. Instrum. Methods Phys. Res., Sect.

A566, 375 (2006).

[19] D. Acosta et al.(CDF Collaboration), Phys. Rev. D71, 052003 (2005).

[20] D. Acostaet al.(CDF Collaboration),Phys. Rev. Lett.97, 082004 (2006).

[21] G. Corcellaet al.,J. High Energy Phys. 01 (2001) 010.

[22] T. Sjostrand et al., Comput. Phys. Commun. 135, 238 (2001).

[23] M. Mangano et al., J. High Energy Phys. 07 (2003) 001.

[24] J. Alwallet al.,J. High Energy Phys. 09 (2007) 028.

[25] G. J. Feldman and R. D. Cousins,Phys. Rev. D57, 3873 (1998).

042002-8