Search for <em>Z′-&gt;e⁺e⁻</em> Using Dielectron Mass and Angular Distribution

Article

Reference

Search for Z′->e

e

Using Dielectron Mass and Angular Distribution

CDF Collaboration

CAMPANELLI, Mario (Collab.), et al.

Abstract

We search for Z′ bosons in dielectron events produced in pp collisions at s√=1.96  TeV, using 0.45  fb−1 of data accumulated with the Collider Detector at Fermilab II detector at the Fermilab Tevatron. To identify the Z′→e+e− signal, both the dielectron invariant mass distribution and the angular distribution of the electron pair are used. No evidence of a signal is found, and 95% confidence level lower limits are set on the Z′ mass for several models.

Limits are also placed on the mass and gauge coupling of a generic Z′, as well as on the contact-interaction mass scales for different helicity structure scenarios.

CDF Collaboration, CAMPANELLI, Mario (Collab.), et al . Search for Z′->e

e

Using Dielectron Mass and Angular Distribution. Physical Review Letters , 2006, vol. 96, no. 21, p. 211801

DOI : 10.1103/PhysRevLett.96.211801

Available at:

http://archive-ouverte.unige.ch/unige:38340

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

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Search for Z

! e

e

Using Dielectron Mass and Angular Distribution

A. Abulencia,²³D. Acosta,¹⁷J. Adelman,¹³T. Affolder,¹⁰T. Akimoto,⁵⁵M. G. Albrow,¹⁶D. Ambrose,¹⁶S. Amerio,⁴³ D. Amidei,³⁴A. Anastassov,⁵²K. Anikeev,¹⁶A. Annovi,¹⁸J. Antos,¹M. Aoki,⁵⁵G. Apollinari,¹⁶J.-F. Arguin,³³ T. Arisawa,⁵⁷A. Artikov,¹⁴W. Ashmanskas,¹⁶A. Attal,⁸F. Azfar,⁴²P. Azzi-Bacchetta,⁴³P. Azzurri,⁴⁶N. Bacchetta,⁴³ H. Bachacou,²⁸W. Badgett,¹⁶A. Barbaro-Galtieri,²⁸V. E. Barnes,⁴⁸B. A. Barnett,²⁴S. Baroiant,⁷V. Bartsch,³⁰G. Bauer,³²

F. Bedeschi,⁴⁶S. Behari,²⁴S. Belforte,⁵⁴G. Bellettini,⁴⁶J. Bellinger,⁵⁹A. Belloni,³²E. Ben Haim,⁴⁴D. Benjamin,¹⁵ A. Beretvas,¹⁶J. Beringer,²⁸T. Berry,²⁹A. Bhatti,⁵⁰M. Binkley,¹⁶D. Bisello,⁴³R. E. Blair,²C. Blocker,⁶B. Blumenfeld,²⁴ A. Bocci,¹⁵A. Bodek,⁴⁹V. Boisvert,⁴⁹G. Bolla,⁴⁸A. Bolshov,³²D. Bortoletto,⁴⁸J. Boudreau,⁴⁷A. Boveia,¹⁰B. Brau,¹⁰

C. Bromberg,³⁵E. Brubaker,¹³J. Budagov,¹⁴H. S. Budd,⁴⁹S. Budd,²³K. Burkett,¹⁶G. Busetto,⁴³P. Bussey,²⁰ K. L. Byrum,²S. Cabrera,¹⁵M. Campanelli,¹⁹M. Campbell,³⁴F. Canelli,⁸A. Canepa,⁴⁸D. Carlsmith,⁵⁹R. Carosi,⁴⁶ S. Carron,¹⁵M. Casarsa,⁵⁴A. Castro,⁵P. Catastini,⁴⁶D. Cauz,⁵⁴M. Cavalli-Sforza,³A. Cerri,²⁸L. Cerrito,⁴²S. H. Chang,²⁷ J. Chapman,³⁴Y. C. Chen,¹M. Chertok,⁷G. Chiarelli,⁴⁶G. Chlachidze,¹⁴F. Chlebana,¹⁶I. Cho,²⁷K. Cho,²⁷D. Chokheli,¹⁴

J. P. Chou,²¹P. H. Chu,²³S. H. Chuang,⁵⁹K. Chung,¹²W. H. Chung,⁵⁹Y. S. Chung,⁴⁹M. Ciljak,⁴⁶C. I. Ciobanu,²³ M. A. Ciocci,⁴⁶A. Clark,¹⁹D. Clark,⁶M. Coca,¹⁵G. Compostella,⁴³M. E. Convery,⁵⁰J. Conway,⁷B. Cooper,³⁰ K. Copic,³⁴M. Cordelli,¹⁸G. Cortiana,⁴³F. Cresciolo,⁴⁶A. Cruz,¹⁷C. Cuenca Almenar,⁷J. Cuevas,¹¹R. Culbertson,¹⁶

D. Cyr,⁵⁹S. DaRonco,⁴³S. D’Auria,²⁰M. D’Onofrio,³D. Dagenhart,⁶P. de Barbaro,⁴⁹S. De Cecco,⁵¹A. Deisher,²⁸ G. De Lentdecker,⁴⁹M. Dell’Orso,⁴⁶F. Delli Paoli,⁴³S. Demers,⁴⁹L. Demortier,⁵⁰J. Deng,¹⁵M. Deninno,⁵D. De Pedis,⁵¹

P. F. Derwent,¹⁶C. Dionisi,⁵¹J. R. Dittmann,⁴P. DiTuro,⁵²C. Do¨rr,²⁵S. Donati,⁴⁶M. Donega,¹⁹P. Dong,⁸J. Donini,⁴³ T. Dorigo,⁴³S. Dube,⁵²K. Ebina,⁵⁷J. Efron,³⁹J. Ehlers,¹⁹R. Erbacher,⁷D. Errede,²³S. Errede,²³R. Eusebi,¹⁶ H. C. Fang,²⁸S. Farrington,²⁹I. Fedorko,⁴⁶W. T. Fedorko,¹³R. G. Feild,⁶⁰M. Feindt,²⁵J. P. Fernandez,³¹R. Field,¹⁷ G. Flanagan,⁴⁸L. R. Flores-Castillo,⁴⁷A. Foland,²¹S. Forrester,⁷G. W. Foster,¹⁶M. Franklin,²¹J. C. Freeman,²⁸I. Furic,¹³

M. Gallinaro,⁵⁰J. Galyardt,¹²J. E. Garcia,⁴⁶M. Garcia Sciveres,²⁸A. F. Garfinkel,⁴⁸C. Gay,⁶⁰H. Gerberich,²³ D. Gerdes,³⁴S. Giagu,⁵¹P. Giannetti,⁴⁶A. Gibson,²⁸K. Gibson,¹²C. Ginsburg,¹⁶N. Giokaris,¹⁴K. Giolo,⁴⁸M. Giordani,⁵⁴ P. Giromini,¹⁸M. Giunta,⁴⁶G. Giurgiu,¹²V. Glagolev,¹⁴D. Glenzinski,¹⁶M. Gold,³⁷N. Goldschmidt,³⁴J. Goldstein,⁴²

G. Gomez,¹¹G. Gomez-Ceballos,¹¹M. Goncharov,⁵³O. Gonza´lez,³¹I. Gorelov,³⁷A. T. Goshaw,¹⁵Y. Gotra,⁴⁷ K. Goulianos,⁵⁰A. Gresele,⁴³M. Griffiths,²⁹S. Grinstein,²¹C. Grosso-Pilcher,¹³R. C. Group,¹⁷U. Grundler,²³ J. Guimaraes da Costa,²¹Z. Gunay-Unalan,³⁵C. Haber,²⁸S. R. Hahn,¹⁶K. Hahn,⁴⁵E. Halkiadakis,⁵²A. Hamilton,³³ B.-Y. Han,⁴⁹J. Y. Han,⁴⁹R. Handler,⁵⁹F. Happacher,¹⁸K. Hara,⁵⁵M. Hare,⁵⁶S. Harper,⁴²R. F. Harr,⁵⁸R. M. Harris,¹⁶

K. Hatakeyama,⁵⁰J. Hauser,⁸C. Hays,¹⁵A. Heijboer,⁴⁵B. Heinemann,²⁹J. Heinrich,⁴⁵M. Herndon,⁵⁹D. Hidas,¹⁵ C. S. Hill,¹⁰D. Hirschbuehl,²⁵A. Hocker,¹⁶A. Holloway,²¹S. Hou,¹M. Houlden,²⁹S.-C. Hsu,⁹B. T. Huffman,⁴² R. E. Hughes,³⁹J. Huston,³⁵J. Incandela,¹⁰G. Introzzi,⁴⁶M. Iori,⁵¹Y. Ishizawa,⁵⁵A. Ivanov,⁷B. Iyutin,³²E. James,¹⁶

D. Jang,⁵²B. Jayatilaka,³⁴D. Jeans,⁵¹H. Jensen,¹⁶E. J. Jeon,²⁷S. Jindariani,¹⁷M. Jones,⁴⁸K. K. Joo,²⁷S. Y. Jun,¹² T. R. Junk,²³T. Kamon,⁵³J. Kang,³⁴P. E. Karchin,⁵⁸Y. Kato,⁴¹Y. Kemp,²⁵R. Kephart,¹⁶U. Kerzel,²⁵V. Khotilovich,⁵³ B. Kilminster,³⁹D. H. Kim,²⁷H. S. Kim,²⁷J. E. Kim,²⁷M. J. Kim,¹²S. B. Kim,²⁷S. H. Kim,⁵⁵Y. K. Kim,¹³L. Kirsch,⁶

S. Klimenko,¹⁷M. Klute,³²B. Knuteson,³²B. R. Ko,¹⁵H. Kobayashi,⁵⁵K. Kondo,⁵⁷D. J. Kong,²⁷J. Konigsberg,¹⁷ A. Korytov,¹⁷A. V. Kotwal,¹⁵A. Kovalev,⁴⁵A. Kraan,⁴⁵J. Kraus,²³I. Kravchenko,³²M. Kreps,²⁵J. Kroll,⁴⁵ N. Krumnack,⁴M. Kruse,¹⁵V. Krutelyov,⁵³S. E. Kuhlmann,²Y. Kusakabe,⁵⁷S. Kwang,¹³A. T. Laasanen,⁴⁸S. Lai,³³

S. Lami,⁴⁶S. Lammel,¹⁶M. Lancaster,³⁰R. L. Lander,⁷K. Lannon,³⁹A. Lath,⁵²G. Latino,⁴⁶I. Lazzizzera,⁴³ T. LeCompte,²J. Lee,⁴⁹J. Lee,²⁷Y. J. Lee,²⁷S. W. Lee,⁵³R. Lefe`vre,³N. Leonardo,³²S. Leone,⁴⁶S. Levy,¹³J. D. Lewis,¹⁶ C. Lin,⁶⁰C. S. Lin,¹⁶M. Lindgren,¹⁶E. Lipeles,⁹T. M. Liss,²³A. Lister,¹⁹D. O. Litvintsev,¹⁶T. Liu,¹⁶N. S. Lockyer,⁴⁵ A. Loginov,³⁶M. Loreti,⁴³P. Loverre,⁵¹R.-S. Lu,¹D. Lucchesi,⁴³P. Lujan,²⁸P. Lukens,¹⁶G. Lungu,¹⁷L. Lyons,⁴²J. Lys,²⁸ R. Lysak,¹E. Lytken,⁴⁸P. Mack,²⁵D. MacQueen,³³R. Madrak,¹⁶K. Maeshima,¹⁶T. Maki,²²P. Maksimovic,²⁴S. Malde,⁴²

G. Manca,²⁹F. Margaroli,⁵R. Marginean,¹⁶C. Marino,²³A. Martin,⁶⁰V. Martin,³⁸M. Martı´nez,³T. Maruyama,⁵⁵ H. Matsunaga,⁵⁵M. E. Mattson,⁵⁸R. Mazini,³³P. Mazzanti,⁵K. S. McFarland,⁴⁹P. McIntyre,⁵³R. McNulty,²⁹A. Mehta,²⁹ S. Menzemer,¹¹A. Menzione,⁴⁶P. Merkel,⁴⁸C. Mesropian,⁵⁰A. Messina,⁵¹M. von der Mey,⁸T. Miao,¹⁶N. Miladinovic,⁶ J. Miles,³²R. Miller,³⁵J. S. Miller,³⁴C. Mills,¹⁰M. Milnik,²⁵R. Miquel,²⁸A. Mitra,¹G. Mitselmakher,¹⁷A. Miyamoto,²⁶ N. Moggi,⁵B. Mohr,⁸R. Moore,¹⁶M. Morello,⁴⁶P. Movilla Fernandez,²⁸J. Mu¨lmensta¨dt,²⁸A. Mukherjee,¹⁶Th. Muller,²⁵ R. Mumford,²⁴P. Murat,¹⁶J. Nachtman,¹⁶J. Naganoma,⁵⁷S. Nahn,³²I. Nakano,⁴⁰A. Napier,⁵⁶D. Naumov,³⁷V. Necula,¹⁷ C. Neu,⁴⁵M. S. Neubauer,⁹J. Nielsen,²⁸T. Nigmanov,⁴⁷L. Nodulman,²O. Norniella,³E. Nurse,³⁰T. Ogawa,⁵⁷S. H. Oh,¹⁵

Y. D. Oh,²⁷T. Okusawa,⁴¹R. Oldeman,²⁹R. Orava,²²K. Osterberg,²²C. Pagliarone,⁴⁶E. Palencia,¹¹R. Paoletti,⁴⁶ V. Papadimitriou,¹⁶A. A. Paramonov,¹³B. Parks,³⁹S. Pashapour,³³J. Patrick,¹⁶G. Pauletta,⁵⁴M. Paulini,¹²C. Paus,³² D. E. Pellett,⁷A. Penzo,⁵⁴T. J. Phillips,¹⁵G. Piacentino,⁴⁶J. Piedra,⁴⁴L. Pinera,¹⁷K. Pitts,²³C. Plager,⁸L. Pondrom,⁵⁹ X. Portell,³O. Poukhov,¹⁴N. Pounder,⁴²F. Prakoshyn,¹⁴A. Pronko,¹⁶J. Proudfoot,²F. Ptohos,¹⁸G. Punzi,⁴⁶J. Pursley,²⁴

J. Rademacker,⁴²A. Rahaman,⁴⁷A. Rakitin,³²S. Rappoccio,²¹F. Ratnikov,⁵²B. Reisert,¹⁶V. Rekovic,³⁷ N. van Remortel,²²P. Renton,⁴²M. Rescigno,⁵¹S. Richter,²⁵F. Rimondi,⁵L. Ristori,⁴⁶W. J. Robertson,¹⁵A. Robson,²⁰

T. Rodrigo,¹¹E. Rogers,²³S. Rolli,⁵⁶R. Roser,¹⁶M. Rossi,⁵⁴R. Rossin,¹⁷C. Rott,⁴⁸A. Ruiz,¹¹J. Russ,¹²V. Rusu,¹³ H. Saarikko,²²S. Sabik,³³A. Safonov,⁵³W. K. Sakumoto,⁴⁹G. Salamanna,⁵¹O. Salto´,³D. Saltzberg,⁸C. Sanchez,³

L. Santi,⁵⁴S. Sarkar,⁵¹L. Sartori,⁴⁶K. Sato,⁵⁵P. Savard,³³A. Savoy-Navarro,⁴⁴T. Scheidle,²⁵P. Schlabach,¹⁶ E. E. Schmidt,¹⁶M. P. Schmidt,⁶⁰M. Schmitt,³⁸T. Schwarz,³⁴L. Scodellaro,¹¹A. L. Scott,¹⁰A. Scribano,⁴⁶F. Scuri,⁴⁶

A. Sedov,⁴⁸S. Seidel,³⁷Y. Seiya,⁴¹A. Semenov,¹⁴L. Sexton-Kennedy,¹⁶I. Sfiligoi,¹⁸M. D. Shapiro,²⁸T. Shears,²⁹ P. F. Shepard,⁴⁷D. Sherman,²¹M. Shimojima,⁵⁵M. Shochet,¹³Y. Shon,⁵⁹I. Shreyber,³⁶A. Sidoti,⁴⁴P. Sinervo,³³

A. Sisakyan,¹⁴J. Sjolin,⁴²A. Skiba,²⁵A. J. Slaughter,¹⁶K. Sliwa,⁵⁶J. R. Smith,⁷F. D. Snider,¹⁶R. Snihur,³³ M. Soderberg,³⁴A. Soha,⁷S. Somalwar,⁵²V. Sorin,³⁵J. Spalding,¹⁶M. Spezziga,¹⁶F. Spinella,⁴⁶T. Spreitzer,³³ P. Squillacioti,⁴⁶M. Stanitzki,⁶⁰A. Staveris-Polykalas,⁴⁶R. St. Denis,²⁰B. Stelzer,⁸O. Stelzer-Chilton,⁴²D. Stentz,³⁸ J. Strologas,³⁷D. Stuart,¹⁰J. S. Suh,²⁷A. Sukhanov,¹⁷K. Sumorok,³²H. Sun,⁵⁶T. Suzuki,⁵⁵A. Taffard,²³R. Takashima,⁴⁰

Y. Takeuchi,⁵⁵K. Takikawa,⁵⁵M. Tanaka,²R. Tanaka,⁴⁰N. Tanimoto,⁴⁰M. Tecchio,³⁴P. K. Teng,¹K. Terashi,⁵⁰ S. Tether,³²J. Thom,¹⁶A. S. Thompson,²⁰E. Thomson,⁴⁵P. Tipton,⁴⁹V. Tiwari,¹²S. Tkaczyk,¹⁶D. Toback,⁵³S. Tokar,¹⁴

K. Tollefson,³⁵T. Tomura,⁵⁵D. Tonelli,⁴⁶M. To¨nnesmann,³⁵S. Torre,¹⁸D. Torretta,¹⁶S. Tourneur,⁴⁴W. Trischuk,³³ R. Tsuchiya,⁵⁷S. Tsuno,⁴⁰N. Turini,⁴⁶F. Ukegawa,⁵⁵T. Unverhau,²⁰S. Uozumi,⁵⁵D. Usynin,⁴⁵A. Vaiciulis,⁴⁹ S. Vallecorsa,¹⁹A. Varganov,³⁴E. Vataga,³⁷G. Velev,¹⁶G. Veramendi,²³V. Veszpremi,⁴⁸R. Vidal,¹⁶I. Vila,¹¹R. Vilar,¹¹

T. Vine,³⁰I. Vollrath,³³I. Volobouev,²⁸G. Volpi,⁴⁶F. Wu¨rthwein,⁹P. Wagner,⁵³R. G. Wagner,²R. L. Wagner,¹⁶ W. Wagner,²⁵R. Wallny,⁸T. Walter,²⁵Z. Wan,⁵²S. M. Wang,¹A. Warburton,³³S. Waschke,²⁰D. Waters,³⁰ W. C. Wester III,¹⁶B. Whitehouse,⁵⁶D. Whiteson,⁴⁵A. B. Wicklund,²E. Wicklund,¹⁶G. Williams,³³H. H. Williams,⁴⁵

P. Wilson,¹⁶B. L. Winer,³⁹P. Wittich,¹⁶S. Wolbers,¹⁶C. Wolfe,¹³T. Wright,³⁴X. Wu,¹⁹S. M. Wynne,²⁹A. Yagil,¹⁶ K. Yamamoto,⁴¹J. Yamaoka,⁵²T. Yamashita,⁴⁰C. Yang,⁶⁰U. K. Yang,¹³Y. C. Yang,²⁷W. M. Yao,²⁸G. P. Yeh,¹⁶J. Yoh,¹⁶

K. Yorita,¹³T. Yoshida,⁴¹G. B. Yu,⁴⁹I. Yu,²⁷S. S. Yu,¹⁶J. C. Yun,¹⁶L. Zanello,⁵¹A. Zanetti,⁵⁴I. Zaw,²¹F. Zetti,⁴⁶ X. Zhang,²³J. 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

14Joint Institute for Nuclear Research, RU-141980 Dubna, Russia

15Duke University, Durham, North Carolina 27708, USA

16Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA

17University of Florida, Gainesville, Florida 32611, USA

18Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy

19University of Geneva, CH-1211 Geneva 4, Switzerland

20Glasgow University, Glasgow G12 8QQ, United Kingdom

21Harvard University, Cambridge, Massachusetts 02138, USA

22Division of High Energy Physics, Department of Physics, University of Helsinki, Helsinki, Finland and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland

23University of Illinois, Urbana, Illinois 61801, USA

211801-2

24The Johns Hopkins University, Baltimore, Maryland 21218, USA

25Institut fu¨r Experimentelle Kernphysik, Universita¨t Karlsruhe, 76128 Karlsruhe, Germany

26High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305, Japan

27Center for High Energy Physics: Kyungpook National University, Taegu 702-701, Korea;

Seoul National University, Seoul 151-742, Korea;

and SungKyunKwan University, Suwon 440-746, Korea

28Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

29University of Liverpool, Liverpool L69 7ZE, United Kingdom

30University College London, London WC1E 6BT, United Kingdom

31Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain

32Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

33Institute of Particle Physics: McGill University, Montre´al, Canada H3A 2T8;

and University of Toronto, Toronto, Canada M5S 1A7

34University of Michigan, Ann Arbor, Michigan 48109, USA

35Michigan State University, East Lansing, Michigan 48824, USA

36Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia

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

43University of Padova, Istituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova, Italy

44LPNHE-Universite Pierre et Marie Curie-Paris 6, IN2P3-CNRS, UMR7585, Paris F-75005 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 21 February 2006; published 30 May 2006) We search for Z⁰ bosons in dielectron events produced in pp collisions at ps

1:96 TeV, using 0:45 fb¹of data accumulated with the Collider Detector at Fermilab II detector at the Fermilab Tevatron.

To identify the Z⁰!ee signal, both the dielectron invariant mass distribution and the angular distribution of the electron pair are used. No evidence of a signal is found, and 95% confidence level lower limits are set on theZ⁰mass for several models. Limits are also placed on the mass and gauge coupling of a genericZ⁰, as well as on the contact-interaction mass scales for different helicity structure scenarios.

DOI:10.1103/PhysRevLett.96.211801 PACS numbers: 13.85.Rm, 12.60.Cn, 13.85.Qk, 14.70.Pw

Many extensions of the standard model (SM) gauge group predict the existence of electrically neutral, massive gauge bosons commonly referred to as Z⁰ [1–5]. The leptonic decays Z⁰!‘‘ provide the most distinctive signature for observing theZ⁰signal at a hadron collider. In two recent publications, the Collider Detector at Fermilab (CDF) Collaboration has set limits on differentZ⁰models by analyzing the invariant mass (M_‘‘) spectrum of the

dielectron, dimuon, and ditau final states, using a dataset corresponding to an integrated luminosity of approxi- mately 0:2 fb¹ [6,7]. Besides the dilepton mass M_‘‘, it has been shown that the angular distribution of the dilepton events can also be used to test the presence of aZ⁰boson by detecting its interference with the SMZboson [8]. In this Letter, for the first time at a hadron collider, the massive resonance search technique (M_‘‘ analysis) is extended to

include dilepton angular information to detectZ⁰!ee decays in0:45 fb¹ of data accumulated with the CDF II detector. As the integrated luminosity increases, the sensi- tivity of the standard M_‘‘ analysis plateaus; adding the angular information starts to become an important handle for extending theZ⁰exclusion reach and discovery poten- tial. In this Letter many of the theoretical Z⁰ models are surveyed, and results are reported for the sequentialZ⁰_SM, the canonical superstring-inspiredE₆ modelsZ,Z ,Z, Z_I,Z_N,Z_sec[9,10], the ‘‘littlest’’ HiggsZ_Hmodel [4,5], the four generic model lines of Ref. [2], and contact- interaction searches. No significant evidence of aZ⁰signal is found, and the tightest constraints to date are set on most of these models.

The CDF detector is described in detail elsewhere [11].

For this study, the relevant subdetector systems are the central tracking chamber (COT) and the central and the plug calorimeters. The COT is a 96-layer open-cell drift chamber immersed in a 1.4 Tesla magnetic field, used to measure charged particle momenta within the pseudora- pidity rangejj<1:0[12]. Surrounding the COT are the electromagnetic and hadronic calorimeters, segmented in projectivetowers pointing to the nominal collision pointz0. The central calorimeters measure the energies of particles within the range jj<1:1, while the plug calorimeters extend the range to 1:1<jj<3:6. Two triggers were used to select the data for this analysis. The main trigger requires two high-E_Telectromagnetic clusters in the calorimeter while a backup trigger accepts events with a single electron candidate with very high E_T and looser electron-selection requirements.

Events are selected with two high-E_T electron candi- dates [13,14], of which at least one is required to have been measured in the central calorimeter. A matching COT track is required for all central candidates. Events with same- sign central electron pairs are rejected, and an isolation condition for the energy found within a cone of angular

radiusR

^{2 2}

p 0:4around the electron is imposed for electron candidates. The angular distribution is measured usingcos, whereis the angle between the electron and the incoming quark in the Collins-Soper frame [15]. The search is performed using events with M_ee>200 GeV=c².

Z⁰production is expected to interfere with the SM Drell- YanZ=process, altering thecosdistribution. For this reason, theZ=process is not labeled as a ‘‘background.’’

Instead, theZ⁰=Z= is referred to as theZ⁰ signal, while the SMZ=is referred to as the SMDrell-Yanproduction.

The term background will be used to designate all other SM processes (excludingZ=) expected to contribute to the dielectron final state sample. Of these background sources, the most important are dijet events in which jets are misidentified as electrons, and diboson events (see Table I). The dijet background is estimated using the probability for a jet to be misidentified as an electron

(‘‘fake rate’’) which is measured in inclusive jet triggered data. The fake rate is then applied to each jet in a sample of events containing one electron candidate and one or more jets. All nondijet backgrounds are estimated usingPYTHIA

[16] Monte Carlo simulation, normalized to the product of the theoretical cross sections [17,18] and the integrated luminosity. Other background processes such as Z=! !ee_ee or top pair production tt! ee_eebb have negligible contributions in the high- mass region considered for this analysis.

A leading-order calculation is used as the starting point to construct the signal and SM Drell-Yan Monte Carlo distributions [19]. A next-to-next-to-leading-order mass- dependent K factor [2] is then included, followed by a (M_ee,cos) parametrization of the CDF detector response [20] to dielectron events. This parametrization is extracted by running the full detector simulation on a large sample of Z= !eeevents generated withPYTHIAsuch that the distribution in M_ee is roughly uniform between 0.03 and 1:05 TeV=c².

For a particularZ⁰model (denoted byH1), we isolate the Z⁰ signal by using two variables: the invariant mass of the dielectron pair M_ee in 10 GeV=c² bins, and cos in 0.25 bins. The bidimensional distribution (M_ee;cos) of the CDF data is used to test two mutually exclusive hy- TABLE I. Summary of the expected and observed numbers of dielectron events with M_ee>200 GeV=c² in 0:45 fb¹. This luminosity value was used to normalize the contributions from all processes with the exception of the dijet background.

Source Z=!ee Dijet Diboson Total SM Observed Events 80:08:0 28¹⁴₁₇ 6:81:4 115¹⁶₁₉ 120

50 100 150 200 250 300 350 400 450 500

Events/10 GeV/c 1 10 10² 10³ 10⁴

50 100 150 200 250 300 350 400 450 500

2

1 10 10² 10³ 10⁴

2

) (GeV/c M

200 250 300 350 400 450 2

6 10 14 2Events / 10 GeV/c18

2 ) (GeV/c Mee

FIG. 1. Meedistribution of the data (points) compared to the prediction for SM Drell-Yan and backgrounds. The individual contributions are stacked as follows: other backgrounds (dark gray), dijet background (light gray), and SM Drell-Yan (open).

The inset shows the M_ee distribution of high-mass data events using a bin size of10 GeV=c². There are no events in the sample withM_ee>500 GeV=c².

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potheses: (1) the null hypothesis (H0), where data are described by SM Drell-Yan and background distributions, and (2) the test hypothesis (H1), where data points are described by theZ⁰signal and background distributions. A test statisticQis defined as

Qd 2 ln~ PdjH1~

PdjH0~ const2X^Nbin

i1

d_ilnN^H1_i N^H0i

where N_bin denotes the total number of bins in the (M_ee;cos) plane,d~ d₁; d₂;. . .; d_Nbinis the observed data distribution, whileN^H1i andN^H0i are the expected numbers of events in bini in the H1 or H0 hypotheses, respectively.

Several sources of systematic uncertainty affect our measurement. First, a relative uncertainty of 10% on the total event rate is incurred primarily due to uncertainties in the luminosity measurement (6%), the dielectron detector acceptance and electron identification efficiency (5%), and the LO calculation (4%). The second dominating effect is the electron energy scale and resolution uncertainty, which modifies the shape of theM_eeandcosdistributions. The third source is the uncertainty in the background (particu- larly dijet) estimations. The dijet prediction uncertainty is extracted from the differences in the fake rate measured in kinematically different jet samples. Finally, the uncertainty related to the choice of the parton distribution functions set (CTEQ6M [21]) is evaluated using the Hessian method advocated in Ref. [22], and found to have a negligible effect on our results.

For each of the Z⁰ models (H1 test hypotheses) men- tioned in the first paragraph, a large number of simulated experiments d~ are drawn either from the H1 or the H0 hypotheses, and the correspondingQd~ values are stored in two separate histograms f^H1Q and f^H0Q, respec- tively. The systematic uncertainties are accounted for as

described in Ref. [23]. The f^H1Q andf^H0Q distribu- tions are integrated in the regionQ > Q₀, whereQ₀is the value measured using thed~distribution of the CDF data. If the ratio of the two integrals is less than 5%, then the H1 model is excluded at 95% confidence level (C.L.) [23].

The CDF data is found to be consistent with the null (no Z⁰) hypothesis, with a probabilityPdjH0~ greater than the values obtained in 87% of H0 simulated experiments.

Figs. 1 and 2 show good agreement between data and Monte Carlo SM distributions for theM_ee andcos dis- tributions. For illustration, Fig. 2 also presents the forward- backward asymmetry A^raw_FB [14] defined as N N=NN, where N andN are the numbers of forward (cos>0) and backward (cos<0) events in the givenM_eerange. The superscript ‘‘raw’’ is used here to emphasize that no detector acceptance, background sub- traction, or efficiency corrections are applied. TheA_FBplot is a common way of representing the mass dependence of the angular distribution.

The sequential Z⁰_SM boson, which has the same cou- plings to fermions as the SMZboson, is excluded by our data up to a mass of 850 GeV=c², at 95% C.L. It is noted here that using the dielectron invariant mass alone would require roughly 25% more data for the same Z⁰_SM exclu- sion. In general, the improvement provided by including the cos spectrum depends strongly on the particular Z⁰ under investigation and the integrated luminosity being analyzed. Other Z⁰ theories include grand unification E₆ -0.8 -0.4 0 0.4 0.8

Events/0.25

5 15 25 35

-0.8 -0.4 0 0.4 0.8 5

15 25

35 Data

- MC +e γ e Z/

Dijet background

θ *) cos(

-0.4 0 0.4 0.8

50 100 200 300 500

Data Expected SM

2

) (GeV/c M

raw FB

A

FIG. 2. Left: Distributions ofcosfor the high-mass regionM_ee>200 GeV=c². The points are the data, the open histograms are the predictions from Drell-Yan Monte Carlo simulation, and the shaded histograms are the background predictions. The individual contributions are stacked. Right: distributions of the forward-backward asymmetry A^raw_FB for the data (points) and predicted SM processes (histogram).

TABLE III. 95% C.L. lower limits for the contact-interaction mass scales.

Interaction LL LR RL RR VV AA

_qe limit (TeV=c²) 3.7 4.7 4.5 3.9 5.6 7.8 _qe limit (TeV=c²) 5.9 5.5 5.8 5.6 8.7 7.8

models [1,3,9], where theE₆gauge group breaks down as E₆ !SO10 U1 !SU5 U1U1 , and the SM gauge structure results from breaking down the SU(5) group. Therefore, an extraZ⁰will be a combination of the twoU1’s:Z_E

6 Z sin_E6Zcos_E6. Table II lists the 95% C.L. lower limits on theM_Z⁰ for theZ,Z , Z,Z_I,Z_N, and the secludedZ_secE₆models.

Another class of theories addressing electroweak sym- metry breaking and the hierarchy problem are the little Higgs theories [4], whereZ⁰_Hbosons are predicted in order to stabilize the Higgs boson mass against quadratically divergent one-loop corrections. In the minimal model of this type (the littlest Higgs model), theZ⁰_Hcouples to left- handed fermions only, and these couplings are parame- trized as functions of the mixing angle cotangentcot_H[5].

Our results forcot_H 0:3, 0.5, 0.7, and 1.0 are shown in Table II, and improve the results reported in Ref. [6].

A recent study reported in Ref. [2] defines a more general set ofZ⁰models. This study uses simple constraints such as generation-independent fermion charges and gauge anomaly cancellations to reduce the number of parameters (17) required to define an arbitraryZ⁰model. Four families of models have been considered, each of them specified by three parameters: the massM_Z⁰, the gauge couplingg_z, and the ratioxof certainU1charges. This three-dimensional parameter space is sampled to obtain the exclusion con- tours shown in Fig. 3. For small jxj and g_z 0:10, the exclusion limits are more stringent than the ones derived in Ref. [2] based on the LEP II results [24].

Finally, Z⁰ mass constraints can be derived from searches for contact interactions, if the collider energy is far below the Z⁰ pole [2,24,25]. An effective Lagrangian for the qqee contact interaction can be written as:

P

q

P

i;jL;R4e_i e_iq_j q_j=²_ij, where is the scale of the interaction, and 1determines the interference structure with the Z= amplitudes [26]. A generation- universal interaction is assumed and lower limits are mea- sured forin six helicity structure scenarios: LL, LR, RL, RR, VV, and AA (Table III) [27].

In conclusion, we have searched forZ⁰ decays toee pairs in 0:45 fb¹ of data accumulated with the CDF II detector. To strengthen this search, the reconstructed di- electron invariant mass M_ee spectrum and the angular distribution of the electron paircos are analyzed simul- taneously. This is the first study of this kind at the Tevatron, and it opens up a new avenue for exploring theZ⁰produc-

tion in the inverse femtobarn luminosity regime. Many of theZ⁰models encountered in the literature are surveyed, no significant evidence for signal is found, and 95% C.L.

limits are set on these models. Constraints are also placed on contact-interaction mass scales far above the Tevatron energy. Finally, exclusion contours for the generic Z⁰ model lines advocated in Ref. [2] are mapped out. In comparison to the LEP contact-interactionZ⁰search results given in [2], our results exhibit higher sensitivity in the smalljxjand smallg_zregions.

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

This work was supported by the U.S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of

-3 -2 -1 0 1 2 3

0 5 10 15 20

-10 -5 0 5 10

0 5 10 15 20 25

-10 -5 0 5 10

5 10 15 20 25

-10 -5 0 5 10

2 6 10 14 18

Charge ratio x Charge ratio x

Charge ratio x Charge ratio x

5 B-xL 10+x

d-xu q+xu

gz= 0.03 gz= 0.10 gz= 0.05 LEP II

)2(TeV/cz /gZ’M)2(TeV/cz /gZ’M

gz= 0.03 gz= 0.10 gz= 0.05 LEP II

gz= 0.03 gz= 0.10 gz= 0.05 LEP II

gz= 0.03 gz= 0.10 gz= 0.05 LEP II

FIG. 3. Exclusion contours for theBxL,10x5,dxu, andqxu Z⁰families. The dotted lines represent the exclusion boundaries derived in Ref. [2] from the LEP II results [24]. The region below each curve is excluded by our data at 95% C.L.

Only models withM_Z⁰>200 GeV=c²are tested, which explains the gap at smalljxjfor some models.

TABLE II. Z⁰exclusion summary: expected and observed 95% C.L. lower limits onM_Z⁰for the sequential, the canonicalE₆, and the littlest HiggsZ⁰models.

Z⁰Model Z_SM Z Z Z Z_I Z_N Z_sec Z^0:3_H Z^0:5_H Z^0:7_H Z^1:0_H

Exp. limit (GeV=c²) 860 735 725 745 650 710 675 625 765 835 910

Obs. limit (GeV=c²) 850 740 725 745 650 710 680 625 760 830 900

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Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Foun- dation; the A. P. Sloan Foundation; the Research Corpo- ration; the Bundesministerium fu¨r Bildung und Forschung, Germany; the Korean Science and Engineering Foundation and the Korean Research Foundation; the Particle Physics and Astronomy Research Council and the Royal Society, UK; the Russian Foundation for Basic Research; the Comisio´n Interministerial de Ciencia y Tecnologı´a, Spain; in part by the European Community’s Human Potential Programme under Contract No. HPRN-CT- 2002-00292; and the Academy of Finland. We thank M.

Carena, B. Dobrescu, P. Langacker, H. Logan, and T. Tait for many fruitful discussions.

[1] F. del Aguila, M. Quiros, and F. Zwirner, Nucl. Phys.

B287, 419 (1987); J. L. Hewett and T. G. Rizzo, Phys. Rep.

183, 193 (1989).

[2] M. Carenaet al., Phys. Rev. D70, 093009 (2004).

[3] J. Erleret al., Phys. Rev. D 66, 015002 (2002); T. Han et al., Phys. Rev. D70, 115006 (2004).

[4] N. Arkani-Hamedet al., J. High Energy Phys. 07 (2002) 034.

[5] T. Hanet al., Phys. Rev. D67, 095004 (2003).

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

95, 252001 (2005).

[7] D. Acostaet al.(CDF Collaboration), Phys. Rev. Lett.95, 131801 (2005).

[8] J. L. Rosner, Phys. Rev. D54, 1078 (1996); T. Affolder et al.(CDF Collaboration), Phys. Rev. Lett. 87, 131802 (2001).

[9] J. L. Rosner, Phys. Rev. D35, 2244 (1987).

[10] J. Kang and P. Langacker, Phys. Rev. D 71, 035014 (2005).

[11] D. Acosta et al. (CDF Collaboration), Phys. Rev. D 71, 032001 (2005); F. Abe et al., Nucl. Instrum. Methods

Phys. Res., Sect. A 271, 387 (1988); D. Amidei et al., ibid. 350, 73 (1994); P. Azzi et al., ibid. 360, 137 (1995).

[12] In the CDF geometry, is the polar angle with respect to the proton beam axis (positive z direction), and is the azimuthal angle. The pseudorapidity is lntan=2. The transverse momentum, pT, is the component of the momentum projected onto the plane perpendicular to the beam axis. The transverse energyE_T of a shower or calorimeter tower isEsin, whereEis the energy deposited.

[13] D. Acostaet al.(CDF Collaboration), Phys. Rev. Lett.94, 091803 (2005).

[14] D. Acosta et al.(CDF Collaboration), Phys. Rev. D71, 052002 (2005).

[15] J. C. Collins and D. E. Soper, Phys. Rev. D 16, 2219 (1977).

[16] T. Sjo¨strand et al., Comput. Phys. Commun. 135, 238 (2001); We usePYTHIAversion 6.129a.

[17] U. Baur, T. Han, and J. Ohnemus, Phys. Rev. D48, 5140 (1993).

[18] J. M. Campbell and R. K. Ellis, Phys. Rev. D60, 113006 (1999).

[19] The couplings we use are detailed in C. Ciobanuet al., Report No. FERMILAB-FN-0773-E, 2005.

[20] GEANT, ‘‘Detector Description and Simulation Tool’’, CERN Program Library Long Writeup W5013, 1993.

[21] H. Laiet al., Phys. Rev. D 51, 4763 (1995); J. Pumplin et al., J. High Energy Phys. 07 (2002) 012.

[22] J. Pumplinet al., Phys. Rev. D65, 014013 (2002).

[23] A. L. Read, J. Phys. G28, 2693 (2002); P. Bocket al.(LEP Collaborations), Report No. CERN-EP-98-046, 1998 and Report No. CERN-EP-2000-055 2000.

[24] D. Abbaneo et al. (LEP Collaborations and SLD Collaboration), Report No. CERN-EP/2003-091, 2003.

[25] F. Abeet al. (CDF Collaboration), Phys. Rev. Lett. 79, 2198 (1997).

[26] E. J. Eichten, K. D. Lane, and M. E. Peskin, Phys. Rev.

Lett.50, 811 (1983).

[27] We use:VVAA LLLR RL RR.