Search for Associated Production of Υ and Vector Boson in <em>pp</em> Collisions at s√=1.8  TeV

Article

Reference

Search for Associated Production of Υ and Vector Boson in pp Collisions at s√=1.8  TeV

CDF Collaboration

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

Abstract

We present a search for associated production of the Υ(1S) and a vector boson in 83   pb−1 of pp¯ collisions at s√=1.8   TeV collected by the CDF experiment in 1994–1995. We find no evidence of the searched signal in the data, and set upper limits to the production cross sections.

CDF Collaboration, CLARK, Allan Geoffrey (Collab.), et al . Search for Associated Production of Υ and Vector Boson in pp Collisions at s√=1.8  TeV. Physical Review Letters , 2003, vol. 90, no. 22, p. 221803

DOI : 10.1103/PhysRevLett.90.221803

Available at:

http://archive-ouverte.unige.ch/unige:38055

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

1 / 1

Search for Associated Production of and Vector Boson in pp Collisions at p s

1:8 TeV

D. Acosta,¹⁴T. Affolder,²⁵H. Akimoto,⁵¹M. G. Albrow,¹³D. Ambrose,³⁷D. Amidei,²⁸K. Anikeev,²⁷J. Antos,¹ G. Apollinari,¹³T. Arisawa,⁵¹A. Artikov,¹¹T. Asakawa,⁴⁹W. Ashmanskas,¹⁰F. Azfar,³⁵P. Azzi-Bacchetta,³⁶ N. Bacchetta,³⁶H. Bachacou,²⁵W. Badgett,¹³S. Bailey,¹⁸P. de Barbaro,⁴¹A. Barbaro-Galtieri,²⁵V. E. Barnes,⁴⁰

B. A. Barnett,²¹S. Baroiant,⁵M. Barone,¹⁵G. Bauer,²⁷F. Bedeschi,³⁸S. Behari,²¹S. Belforte,⁴⁸W. H. Bell,¹⁷ G. Bellettini,³⁸J. Bellinger,⁵²D. Benjamin,¹²J. Bensinger,⁴A. Beretvas,¹³J. Berryhill,¹⁰A. Bhatti,⁴²M. Binkley,¹³ D. Bisello,³⁶M. Bishai,¹³R. E. Blair,²C. Blocker,⁴K. Bloom,²⁸B. Blumenfeld,²¹S. R. Blusk,⁴¹A. Bocci,⁴²A. Bodek,⁴¹ G. Bolla,⁴⁰A. Bolshov,²⁷Y. Bonushkin,⁶D. Bortoletto,⁴⁰J. Boudreau,³⁹A. Brandl,³¹C. Bromberg,²⁹M. Brozovic,¹²

E. Brubaker,²⁵N. Bruner,³¹J. Budagov,¹¹H. S. Budd,⁴¹K. Burkett,¹⁸G. Busetto,³⁶K. L. Byrum,²S. Cabrera,¹² P. Calafiura,²⁵M. Campbell,²⁸W. Carithers,²⁵J. Carlson,²⁸D. Carlsmith,⁵²W. Caskey,⁵A. Castro,³D. Cauz,⁴⁸ A. Cerri,³⁸L. Cerrito,²⁰A.W. Chan,¹P. S. Chang,¹P. T. Chang,¹J. Chapman,²⁸C. Chen,³⁷Y. C. Chen,¹M.-T. Cheng,¹

M. Chertok,⁵G. Chiarelli,³⁸I. Chirikov-Zorin,¹¹G. Chlachidze,¹¹F. Chlebana,¹³L. Christofek,²⁰M. L. Chu,¹ J. Y. Chung,³³W.-H. Chung,⁵²Y. S. Chung,⁴¹C. I. Ciobanu,³³A. G. Clark,¹⁶M. Coca,⁴¹A. P. Colijn,¹³A. Connolly,²⁵ M. Convery,⁴²J. Conway,⁴⁴M. Cordelli,¹⁵J. Cranshaw,⁴⁶R. Culbertson,¹³D. Dagenhart,⁴S. D’Auria,¹⁷S. De Cecco,⁴³

F. DeJongh,¹³ S. Dell’Agnello,¹⁵ M. Dell’Orso,³⁸S. Demers,⁴¹L. Demortier,⁴²M. Deninno,³D. De Pedis,⁴³ P. F. Derwent,¹³T. Devlin,⁴⁴C. Dionisi,⁴³J. R. Dittmann,¹³A. Dominguez,²⁵S. Donati,³⁸M. D’Onofrio,³⁸T. Dorigo,³⁶ N. Eddy,²⁰K. Einsweiler,²⁵E. Engels, Jr.,³⁹R. Erbacher,¹³D. Errede,²⁰S. Errede,²⁰R. Eusebi,⁴¹Q. Fan,⁴¹H.-C. Fang,²⁵

S. Farrington,¹⁷ R. G. Feild,⁵³J. P. Fernandez,⁴⁰C. Ferretti,²⁸R. D. Field,¹⁴I. Fiori,³B. Flaugher,¹³

L. R. Flores-Castillo,³⁹G.W. Foster,¹³M. Franklin,¹⁸J. Freeman,¹³J. Friedman,²⁷Y. Fukui,²³I. Furic,²⁷S. Galeotti,³⁸ A. Gallas,³²M. Gallinaro,⁴²T. Gao,³⁷M. Garcia-Sciveres,²⁵A. F. Garfinkel,⁴⁰P. Gatti,³⁶C. Gay,⁵³D.W. Gerdes,²⁸

E. Gerstein,⁹S. Giagu,⁴³P. Giannetti,³⁸K. Giolo,⁴⁰M. Giordani,⁵P. Giromini,¹⁵V. Glagolev,¹¹D. Glenzinski,¹³ M. Gold,³¹N. Goldschmidt,²⁸J. Goldstein,¹³G. Gomez,⁸M. Goncharov,⁴⁵I. Gorelov,³¹A. T. Goshaw,¹²Y. Gotra,³⁹

K. Goulianos,⁴²C. Green,⁴⁰A. Gresele,³⁶G. Grim,⁵C. Grosso-Pilcher,¹⁰M. Guenther,⁴⁰G. Guillian,²⁸ J. Guimaraes da Costa,¹⁸R. M. Haas,¹⁴C. Haber,²⁵S. R. Hahn,¹³E. Halkiadakis,⁴¹C. Hall,¹⁸T. Handa,¹⁹R. Handler,⁵² F. Happacher,¹⁵K. Hara,⁴⁹A. D. Hardman,⁴⁰R. M. Harris,¹³F. Hartmann,²²K. Hatakeyama,⁴²J. Hauser,⁶J. Heinrich,³⁷

A. Heiss,²²M. Hennecke,²²M. Herndon,²¹C. Hill,⁷A. Hocker,⁴¹K. D. Hoffman,¹⁰R. Hollebeek,³⁷L. Holloway,²⁰ S. Hou,¹B. T. Huffman,³⁵R. Hughes,³³J. Huston,²⁹J. Huth,¹⁸H. Ikeda,⁴⁹J. Incandela,⁷G. Introzzi,³⁸M. Iori,⁴³

A. Ivanov,⁴¹J. Iwai,⁵¹Y. Iwata,¹⁹B. Iyutin,²⁷E. James,²⁸M. Jones,³⁷U. Joshi,¹³H. Kambara,¹⁶T. Kamon,⁴⁵ T. Kaneko,⁴⁹J. Kang,²⁸M. Karagoz Unel,³²K. Karr,⁵⁰S. Kartal,¹³H. Kasha,⁵³Y. Kato,³⁴T. A. Keaffaber,⁴⁰K. Kelley,²⁷

M. Kelly,²⁷R. D. Kennedy,¹³R. Kephart,¹³D. Khazins,¹²T. Kikuchi,⁴⁹B. Kilminster,⁴¹B. J. Kim,²⁴ D. H. Kim,²⁴ H. S. Kim,²⁰M. J. Kim,⁹S. B. Kim,²⁴S. H. Kim,⁴⁹T. H. Kim,²⁷Y. K. Kim,²⁵M. Kirby,¹²M. Kirk,⁴L. Kirsch,⁴ S. Klimenko,¹⁴ P. Koehn,³³K. Kondo,⁵¹J. Konigsberg,¹⁴A. Korn,²⁷A. Korytov,¹⁴K. Kotelnikov,³⁰E. Kovacs,²

J. Kroll,³⁷M. Kruse,¹²V. Krutelyov,⁴⁵S. E. Kuhlmann,²K. Kurino,¹⁹T. Kuwabara,⁴⁹N. Kuznetsova,¹³ A. T. Laasanen,⁴⁰K.W. Lai,^54,* N. Lai,¹⁰S. Lami,⁴²S. Lammel,¹³J. Lancaster,¹²K. Lannon,²⁰M. Lancaster,²⁶

R. Lander,⁵A. Lath,⁴⁴G. Latino,³¹T. LeCompte,²Y. Le,²¹J. Lee,⁴¹S.W. Lee,⁴⁵N. Leonardo,²⁷S. Leone,³⁸ J. D. Lewis,¹³K. Li,⁵³C. S. Lin,¹³M. Lindgren,⁶T. M. Liss,²⁰J. B. Liu,⁴¹T. Liu,¹³Y. C. Liu,¹D. O. Litvintsev,¹³ O. Lobban,⁴⁶N. S. Lockyer,³⁷A. Loginov,³⁰J. Loken,³⁵M. Loreti,³⁶D. Lucchesi,³⁶P. Lukens,¹³S. Lusin,⁵²L. Lyons,³⁵

J. Lys,²⁵R. Madrak,¹⁸K. Maeshima,¹³P. Maksimovic,²¹L. Malferrari,³M. Mangano,³⁸G. Manca,³⁵M. Mariotti,³⁶ G. Martignon,³⁶M. Martin,²¹A. Martin,⁵³V. Martin,³²J. A. J. Matthews,³¹P. Mazzanti,³K. S. McFarland,⁴¹ P. McIntyre,⁴⁵M. Menguzzato,³⁶A. Menzione,³⁸P. Merkel,¹³C. Mesropian,⁴²A. Meyer,¹³T. Miao,¹³R. Miller,²⁹ J. S. Miller,²⁸H. Minato,⁴⁹S. Miscetti,¹⁵M. Mishina,²³G. Mitselmakher,¹⁴Y. Miyazaki,³⁴N. Moggi,³E. Moore,³¹ R. Moore,²⁸Y. Morita,²³T. Moulik,⁴⁰M. Mulhearn,²⁷A. Mukherjee,¹³T. Muller,²²A. Munar,³⁸P. Murat,¹³S. Murgia,²⁹ J. Nachtman,⁶V. Nagaslaev,⁴⁶S. Nahn,⁵³H. Nakada,⁴⁹I. Nakano,¹⁹R. Napora,²¹F. Niell,²⁸C. Nelson,¹³T. Nelson,¹³

C. Neu,³³M. S. Neubauer,²⁷D. Neuberger,²²C. Newman-Holmes,¹³C.-Y. P. Ngan,²⁷T. Nigmanov,³⁹H. Niu,⁴ L. Nodulman,²A. Nomerotski,¹⁴S. H. Oh,¹²Y. D. Oh,²⁴T. Ohmoto,¹⁹T. Ohsugi,¹⁹R. Oishi,⁴⁹T. Okusawa,³⁴J. Olsen,⁵² W. Orejudos,²⁵C. Pagliarone,³⁸F. Palmonari,³⁸R. Paoletti,³⁸V. Papadimitriou,⁴⁶D. Partos,⁴J. Patrick,¹³G. Pauletta,⁴⁸ M. Paulini,⁹T. Pauly,³⁵C. Paus,²⁷D. Pellett,⁵A. Penzo,⁴⁸L. Pescara,³⁶T. J. Phillips,¹²G. Piacentino,³⁸J. Piedra,⁸ K. T. Pitts,²⁰A. Pompos˘,⁴⁰L. Pondrom,⁵²G. Pope,³⁹T. Pratt,³⁵F. Prokoshin,¹¹J. Proudfoot,²F. Ptohos,¹⁵O. Pukhov,¹¹

G. Punzi,³⁸J. Rademacker,³⁵A. Rakitine,²⁷F. Ratnikov,⁴⁴H. Ray,²⁸D. Reher,²⁵A. Reichold,³⁵P. Renton,³⁵ M. Rescigno,⁴³A. Ribon,³⁶W. Riegler,¹⁸F. Rimondi,³L. Ristori,³⁸M. Riveline,⁴⁷W. J. Robertson,¹²T. Rodrigo,⁸

S. Rolli,⁵⁰L. Rosenson,²⁷R. Roser,¹³R. Rossin,³⁶C. Rott,⁴⁰A. Roy,⁴⁰A. Ruiz,⁸D. Ryan,⁵⁰A. Safonov,⁵R. St. Denis,¹⁷ W. K. Sakumoto,⁴¹D. Saltzberg,⁶C. Sanchez,³³A. Sansoni,¹⁵L. Santi,⁴⁸S. Sarkar,⁴³H. Sato,⁴⁹P. Savard,⁴⁷ A. Savoy-Navarro,¹³P. Schlabach,¹³E. E. Schmidt,¹³M. P. Schmidt,⁵³M. Schmitt,³²L. Scodellaro,³⁶A. Scott,⁶ A. Scribano,³⁸A. Sedov,⁴⁰S. Seidel,³¹Y. Seiya,⁴⁹A. Semenov,¹¹F. Semeria,³T. Shah,²⁷M. D. Shapiro,²⁵P. F. Shepard,³⁹

T. Shibayama,⁴⁹M. Shimojima,⁴⁹M. Shochet,¹⁰A. Sidoti,³⁶J. Siegrist,²⁵A. Sill,⁴⁶P. Sinervo,⁴⁷P. Singh,²⁰ A. J. Slaughter,⁵³K. Sliwa,⁵⁰F. D. Snider,¹³R. Snihur,²⁶A. Solodsky,⁴²J. Spalding,¹³T. Speer,¹⁶M. Spezziga,⁴⁶

P. Sphicas,²⁷F. Spinella,³⁸M. Spiropulu,¹⁰L. Spiegel,¹³J. Steele,⁵²A. Stefanini,³⁸J. Strologas,²⁰F. Strumia,¹⁶ D. Stuart,⁷A. Sukhanov,¹⁴K. Sumorok,²⁷T. Suzuki,⁴⁹T. Takano,³⁴R. Takashima,¹⁹K. Takikawa,⁴⁹P. Tamburello,¹²

M. Tanaka,⁴⁹B. Tannenbaum,⁶M. Tecchio,²⁸R. J. Tesarek,¹³P. K. Teng,¹K. Terashi,⁴²S. Tether,²⁷A. S. Thompson,¹⁷ E. Thomson,³³R. Thurman-Keup,²P. Tipton,⁴¹S. Tkaczyk,¹³D. Toback,⁴⁵K. Tollefson,²⁹D. Tonelli,³⁸ M. Tonnesmann,²⁹H. Toyoda,³⁴W. Trischuk,⁴⁷J. F. de Troconiz,¹⁸J. Tseng,²⁷D. Tsybychev,¹⁴N. Turini,³⁸F. Ukegawa,⁴⁹ T. Unverhau,¹⁷T. Vaiciulis,⁴¹J. Valls,⁴⁴A. Varganov,²⁸E. Vataga,³⁸S. Vejcik III,¹³G. Velev,¹³G. Veramendi,²⁵R. Vidal,¹³

I. Vila,⁸R. Vilar,⁸I. Volobouev,²⁵M. von der Mey,⁶D. Vucinic,²⁷R. G. Wagner,²R. L. Wagner,¹³W. Wagner,²² N. B. Wallace,⁴⁴Z. Wan,⁴⁴C. Wang,¹²M. J. Wang,¹S. M. Wang,¹⁴ B. Ward,¹⁷S. Waschke,¹⁷T. Watanabe,⁴⁹D. Waters,²⁶

T. Watts,⁴⁴ M. Weber,²⁵H. Wenzel,²²W. C. Wester III,¹³B. Whitehouse,⁵⁰A. B. Wicklund,²E. Wicklund,¹³T. Wilkes,⁵ H. H. Williams,³⁷P. Wilson,¹³B. L. Winer,³³D. Winn,²⁸S. Wolbers,¹³D. Wolinski,²⁸J. Wolinski,²⁹S. Wolinski,²⁸ M. Wolter,⁵⁰S. Worm,⁴⁴X. Wu,¹⁶F. Wu¨rthwein,²⁷J. Wyss,³⁸U. K. Yang,¹⁰W. Yao,²⁵G. P. Yeh,¹³P. Yeh,¹K. Yi,²¹J. Yoh,¹³

C. Yosef,²⁹T. Yoshida,³⁴I. Yu,²⁴S. Yu,³⁷Z. Yu,⁵³J. C. Yun,¹³L. Zanello,⁴³A. Zanetti,⁴⁸F. Zetti,²⁵and S. Zucchelli³ (CDF Collaboration)

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

2Argonne National Laboratory, Argonne, Illinois 60439, USA

3Istituto Nazionale di Fisica Nucleare, University of Bologna, I-40127 Bologna, Italy

4Brandeis University, Waltham, Massachusetts 02254, USA

5University of California at Davis, Davis, California 95616, USA

6University of California at Los Angeles, Los Angeles, California 90024, USA

7University of California at Santa Barbara, Santa Barbara, California 93106, USA

8Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain

9Carnegie Mellon University, Pittsburgh, Pennsylvania 15218, USA

10Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA

11Joint Institute for Nuclear Research, RU-141980 Dubna, Russia

12Duke University, Durham, North Carolina 27708, USA

13Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA

14University of Florida, Gainesville, Florida 32611, USA

15Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy

16University of Geneva, CH-1211 Geneva 4, Switzerland

17Glasgow University, Glasgow G12 8QQ, United Kingdom

18Harvard University, Cambridge, Massachusetts 02138, USA

19Hiroshima University, Higashi-Hiroshima 724, Japan

20University of Illinois, Urbana, Illinois 61801, USA

21The Johns Hopkins University, Baltimore, Maryland 21218, USA

22Institut fu¨r Experimentelle Kernphysik, Universita¨t Karlsruhe, 76128 Karlsruhe, Germany

23High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305, Japan

24Center for High Energy Physics, Kyungpook National University, Taegu 702-701; Seoul National University, Seoul 151-742;

and SungKyunKwan University, Suwon 440-746; Korea

25Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

26University College London, London WC1E 6BT, United Kingdom

27Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

28University of Michigan, Ann Arbor, Michigan 48109, USA

29Michigan State University, East Lansing, Michigan 48824, USA

30Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia

31University of New Mexico, Albuquerque, New Mexico 87131, USA

32Northwestern University, Evanston, Illinois 60208, USA

33The Ohio State University, Columbus, Ohio 43210, USA

34Osaka City University, Osaka 588, Japan

35University of Oxford, Oxford OX1 3RH, United Kingdom

221803-2 221803-2

36Universita di Padova, Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy

37University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA

38Istituto Nazionale di Fisica Nucleare, University and Scuola Normale Superiore of Pisa, I-56100 Pisa, Italy

39University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA

40Purdue University, West Lafayette, Indiana 47907, USA

41University of Rochester, Rochester, New York 14627, USA

42Rockefeller University, New York, New York 10021, USA

43Instituto Nazionale de Fisica Nucleare, Sezione di Roma, University di Roma I, ‘‘La Sapienza,’’ I-00185 Roma, Italy

44Rutgers University, Piscataway, New Jersey 08855, USA

45Texas A&M University, College Station, Texas 77843, USA

46Texas Tech University, Lubbock, Texas 79409, USA

47Institute of Particle Physics, University of Toronto, Toronto M5S 1A7, Canada

48Istituto Nazionale di Fisica Nucleare, University of Trieste, Udine, Italy

49University of Tsukuba, Tsukuba, Ibaraki 305, Japan

50Tufts University, Medford, Massachusetts 02155, USA

51Waseda University, Tokyo 169, Japan

52University of Wisconsin, Madison, Wisconsin 53706, USA

53Yale University, New Haven, Connecticut 06520, USA

54Universita’ di Padova, Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy (Received 9 December 2002; published 6 June 2003)

We present a search for associated production of the1Sand a vector boson in 83 pb¹ of ppp collisions atps

1:8 TeVcollected by the CDF experiment in 1994 –1995. We find no evidence of the searched signal in the data, and set upper limits to the production cross sections.

DOI: 10.1103/PhysRevLett.90.221803 PACS numbers: 13.20.Gd, 13.85.Rm, 14.70.Fm, 14.70.Hp

The production of mesons associated with vector bosons was examined in a recent paper [1], where expec- tations at the Tevatronppp collider in the standard model (SM) framework were given. The cross section estimates of Ref. [1] forps

1:8 TeVare of the order of 0.47 and 0.18 pb for1SWand1SZproduction, respectively.

In the context of supersymmetric models (SUSY), a charged Higgs boson lighter than about 180 GeV=c² can have a sizable branching ratio intoW pairs if the ratio of vacuum expectation valuestan is small, and similarly a light neutral scalar can decay toZpairs [2].

Although the rates of the SM decays are predicted to be too small to be observable at the Tevatron with currently available statistics, model uncertainties are large, and a search for these processes in the present data, which has never been performed before, is useful for extrapolations to future searches in the SUSY sector.

The main SM production mechanism proceeds through the creation of a vector boson together with a bbb pair which binds to form a1S. The process is described by nonperturbative matrix elements based on the relative velocity of theb quarks in the pair; the formation of a bbbpair has been considered both in color singlet and octet configurations [3]. Additional contributions to the1S signal due to the feed-down from higher bottomonium states, mainly2Sand3S, account for20%of the total production [1].

The data used in this analysis were collected by CDF during the 1994 –1995 run of the Tevatron collider, and correspond to an integrated luminosity ofR

Ldt 83:43:4 pb¹.

The CDF detector has been described in detail else- where [4]. We briefly describe here the portions of the detector used in this analysis. CDF consists of a magnetic spectrometer surrounded by calorimeters and muon chambers. The momenta of charged particles are mea- sured out to a pseudorapidity [5] of jj<1:1 in the central tracking chamber (CTC), which is inside a 1.4 T superconducting solenoidal magnet. The silicon micro- strip vertex detector (SVX) [6], located immediately out- side the beam pipe, provides precise track reconstruction in the plane transverse to the beam. Energy and direction of electrons, photons, and jets are measured by three calorimeter systems covering the central (jj<1:1), in- termediate (1:1<jj<2:4), and forward (jj>2:4) re- gions; each calorimeter has an electromagnetic (EM) and a hadronic (HAD) section. The central muon detection system (CMU) consists of drift chambers located outside the calorimeter, allowing the reconstruction of track seg- ments for penetrating particles. An additional set of chambers (CMP) instrumented with scintillation coun- ters is located outside a 0.6 m thick iron wall, providing additional discrimination against punch-through had- rons. Muons with0:6<jj<1:0are detected by another set of drift chambers (CMX) sandwiched between scin- tillation counters. mesons are thus easily identified through their decay to pairs, while vector bosons are selected via their decay to leptons or to jets of hadrons. The present search focuses on the identification of the1Sstate only due to the lower branching frac- tion of the 2Sand3Sto the final state and to their sizable feed-down to the1Sstate.

The samples of data used in this analysis were col- lected by means of two different three-level muon trig- gers. The first was a dimuon trigger that selected events with two tracks detected in the CMU chambers with transverse momentum P_T >2:2 GeV=c as measured by the Central Fast Tracker (CFT), a hardware track processor with a momentum resolution of P_T=P²_T 0:03GeV=c¹. At least one of the muons had to be detected also in the CMP chambers. The second trig- ger was used to identify single muon candidates. It re- quired that a track segment found at Level 1 in the CMU and CMP detectors matched a CFT track with P_T >

7:5 GeV=c.

Offline muon identification started with the require- ment that the energy deposited in the calorimeter by the candidate be consistent with that of a minimum ionizing particle: we required E^EM_T <1 GeV in the electromag- netic section, E^HAD_T <4 GeV in the hadronic section, and E^EM_T E^HAD_T >0:1 GeV. Pairs of opposite-charge muon tracks are required to have a difference inzcoor- dinates at the point of closest approach to the beam axis within 5 cm. To further reduce fake muon backgrounds, an optimized selection was performed using the²of the three-dimensional match of the CTC track with the seg- ment in the muon chambers. In addition, the impact parameter significance of muon tracks reconstructed by the SVX was used to get rid also of heavy flavor semi- leptonic decays, enhancing the prompt production of muons. The invariant mass of muon pairs was required to be in the 8 to 12 GeV=c² range. Figure 1 shows the resulting dimuon mass spectrum. We estimate the number of events due to1Sproduction to be514396.

The Herwig generator [7] was used to generate1S vector boson events. TheP_Tdifferential cross sections for the hard production processes of 1SW and1SZ⁰ were supplied by the authors of Ref. [1] and introduced into the generator. The 1S was forced to decay to . A detailed simulation of the CDF detector and a full reconstruction were applied to the events, which were then filtered using a simulation of the dimuon and single muon trigger conditions.

mesons produced in association with vector bosons are characterized by a high P_T with respect to other production processes, as shown in Fig. 2. Therefore, events withP_T>5 GeV=cwere selected.

The search for a signal of vector boson decay in the selected data was performed using four independent ex- perimental signatures: the detection of high-E_Telectrons, high-P_T muons, significant missing transverse energy (6E_T), or pairs of hadronic jets. The 6E_T constitutes an independent signal of W! or Z⁰! decays, as well as a tag of W decays to unidentified electrons or muons.

In order to have maximum sensitivity to the searched signal the selection of electrons and muons was looser than that normally used for the collection of W and Z bosons at CDF [8]. Electron candidates were selected by requiring an electromagnetic cluster in the calorimeter with E_T >20 GeV, limiting the energy deposited in the hadronic section by E^HAD=E^EM<0:05, and associ- ating a reconstructed track in the CTC with P_T >

10 GeV=c that satisfies E=P <1:8. Muon candidates must haveP_T >20 GeV=cand an energy deposit in the

0 1000 2000

8 9 10 11 12

Invariant mass of opposite-sign muon pair (GeV/c²)

Events

All events Rejected events Selected events

Mass (GeV/c²) 0

2000

8 10 12

FIG. 1 (color online). Invariant mass of the two opposite- charge muons before (inset) and after (full-scale histogram) the selection of good muon pairs described in the text.

P_T of muon pair (GeV/c)

Events

Sideband-subtracted (1S)ϒ W MC (arbitrary normalization)ϒ Z MC (arbitrary normalization)ϒ

0 500 1000

0 20 40 60

FIG. 2 (color online). Transverse momentum of background- subtracted1Scandidates in the data (full circles) compared to 1S mesons from the SM simulation of 1SW and 1SZ⁰production (empty triangles and squares), with arbi- trary normalization.

221803-4 221803-4

calorimeter consistent with that produced by minimum ionizing particles, as described for the -decay muons above.

The presence of undetected high-P_T neutrinos was inferred by the significance of missing transverse energy s 6E_T=6E_T >3, where6E_Tand6E_T100%

E_T=GeV p

were computed using all calorimeter towers withjj<

3:6. The missingE_T was also corrected for the presence of minimum ionizing particles and mismeasured jets.

Hadronic jets were reconstructed with a R ^{2 2}

p 0:4cone algorithm and selected if they had measuredE_T >10 GeVandjj<2:0. The energy of the two leading jets was then corrected for calorimeter nonlinearities, energy deposited outside the jet cone, contributions from the underlying event, and energy lost in uninstrumented regions of the detector. The dijet in- variant mass, M_jj, was computed, and required to be within the range 65 to 110 GeV=c². The background from semileptonic decays of heavy flavors was effectively reduced by discarding events where a-decay muon is contained in the cone of a leading jet. The identification of vector bosons in the hadronic final state was hindered by a large contamination from QCD processes, and additional conditions were needed to reduce the back- ground in this channel. We optimized the sensitivity by a kinematic selection which requires P_T >14 GeV=c and <1:4. While producing a relative decrease of signal acceptance by 25%, these cuts reduce the background-dominated data by a factor of 6.

Dimuon events characterized by one of the four signa- tures described above were selected asW=Z⁰ candi- dates. A total of 28 events were accepted by the selection;

their dimuon invariant mass spectrum is shown in Fig. 3.

Three events have dimuon mass in the 1S search window, defined as 9:3< M<9:6 GeV=c². All of them are due to the hadronic identification mode of vector bosons. The acceptance for the1SW=Z⁰processes, based on the criteria described above, is reported in Table I. We estimate a SM contribution to our dataset equal to 0.03 and 0.01 signal events from1SW and 1SZ⁰ production, respectively.

Various processes such asbbb, ttt, W=Z, and Drell-Yan production represent possible background con- taminations. However, they are not expected to show any resonant behavior in the invariant mass spectrum. In Fig. 1 clear1S9460production is evi- dent in the 9.3 to9:6 GeV=c² mass region. Nonresonant behavior is observed in the rest of the spectrum with the exception of the regions 9:85–10:15 GeV=c² and 10:2–10:5 GeV=c² that are enriched, respectively, with 2S10023and3S10355decays. The background evaluations described below are extracted from the non- resonant component of experimental data (in the follow- ing simply denoted as ‘‘continuum’’) and from events with kinematic and identification biases similar to those

of signal candidates, for each identification mode of the vector bosons.

The contribution of high-E_T electron events with a dimuon mass in the1Swindow is estimated by scaling the number of continuum events with high-E_T electron candidates by the ratio between 1S and continuum computed in a sample containing a ‘‘fake electron.’’

The fake electron is defined as a central E_T >20 GeV jet with aP_T >10 GeV=ctrack in its cone. The number of expected background events computed is0:0 ^0:3_0:0.

A similar method is used for the background evalu- ation in the muon channel. Events containing nonmuon tracks withP_T >20 GeV=care counted in the1Sand continuum regions, and their ratio is used to extrapolate the number of continuum events with high-P_T muon candidates to the1Swindow. The number of expected background events computed is0:0 ^0:6_0:0.

In the sample of events with6E_T significance,s >3, the number of background events in the 1S window is estimated by rescaling the number of continuum events by the ratio between 1S and continuum computed in an orthogonal sample enhanced in fake missing E_T. This sample is defined by selecting events withs <3and 6E_T >20 GeV. This results in a background prediction of 1:40:8events.

The main sources of background in the hadronic chan- nel are due to Drell-Yan radiative processes and heavy flavor production with semileptonic decay to muons.

These processes show a smooth behavior in the dimuon invariant mass spectrum and in the M_jj spectrum.

Therefore, the fraction of events with 65< M_jj<

110 GeV=c² is expected to be the same in the 1S Invariant mass of muon pair (GeV/c²)

Events

Jet channel candidates Lepton channels candidates

10^-1 10 10³

8 10 12

FIG. 3 (color online). Invariant mass of the two muons for events selected in the four search channels; the region within vertical lines defines 1SW=1SZ⁰ candidates. The dis- tribution of all dimuon candidates before the vector boson selection is overlaid.

region and in the continuum. With that hypothesis, the expected background contamination in the 1SW= 1SZ⁰ channel is 2:11:2events. The estimated and observed numbers of events in the four channels are summarized in Table I, together with the SM acceptance to1SWand1SZ⁰.

Several systematic effects on the acceptance were esti- mated. The use of different parton distribution function sets in the generator can change the total acceptance by about2%. The color-octet contribution to the process is affected by a large uncertainty in this model; its variation produces an uncertainty of1:9%. The dominant system- atic uncertainties in the electron, muon, and6E_T channels are detector effects, trigger modeling, and the identifica- tion of 1S ! decays. Dimuon acceptance, which includes trigger modeling and lepton identification cuts, carries a total systematic uncertainty of7:0%, due to the combined uncertainty on the modeling of selection variables. This was estimated by comparing real muons in the data and in the simulation. Another source of uncertainty is the momentum scale of muon tracks, which may affect the acceptance of the dimuon mass window cut. We estimated the size of the uncertainty by varying the scale by the observed difference (0:2%) between measured and true value of the 1Smass in the data.

In addition, we estimated a3:0%systematic uncertainty on the acceptance of the missingE_T cut. The systematic error on the acceptance in the hadronic channel is domi- nated by the uncertainty on jet energy scale, and is estimated conservatively from a 10%variation of the

jet energy measurement. The relative contribution of each systematic uncertainty is reported in Table II.

We computed cross section limits for the searched SM processes with a counting experiment by combining the four channels together, accounting for the total expected background of 3:5 ^1:6_1:5 events, the estimated acceptance, and the related systematics according to the method de- scribed in [9]. The95%C.L. upper limits obtained are the following:

ppp !1SW X B1S !<2:3 pb;

ppp !1SZ⁰ X B1S !<2:5 pb:

In conclusion, we have not observed1S mesons in association withW orZ⁰ bosons. The sensitivity of the CDF experiment in run I is not sufficient to test the SM prediction of [1] for these processes. With the expected run II increase of integrated luminosity and the upgrades of the CDF detector, we expect to achieve a sensitivity sufficient to observe the plus vector boson production processes.

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, Science, Sports and Culture of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Foundation; the A. P.

Sloan Foundation; the Bundesministerium fu¨r Bildung und Forschung, Germany; and the Korea Science and Engineering Foundation.

*Visitor.

[1] E. Braaten, J. Lee, and S. Fleming, Phys. Rev. D 60, 91501 (1999).

[2] J. A. Grifols, J. F. Gunion, and A. Mendez, Phys. Lett. B 197, 266 (1987); R.W. Robinett and L. Weinkauf, Mod.

Phys. Lett. A6, 1575 (1991).

[3] G. T. Bodwin, E. Braaten, and G. P. Lepage, Phys. Rev. D 51, 1125 (1995).

[4] F. Abeet al., Nucl. Instrum. Methods Phys. Res., Sect. A 271, 387 (1988).

TABLE II. Systematic uncertainties on signal acceptance.

Dimuon acceptance 7:0%

Integrated luminosity 4:1%

1Smass window 2:7%

PDF 2:0%

Color octet contribution 1:9%

s >3cut (6E_T channel only) 3:0%

Jet energy scale (W!jj) 17:2%

Jet energy scale (Z⁰!jj) 11:7%

Total (e; ;6E_Tchannels) 9:0%

Total (W!jj) 19:2%

Total (Z⁰!jj) 14:5%

TABLE I. Number of events in the data after all cuts and results of acceptance and background estimates.

Acceptance (%) Events

Channel 1SW 1SZ⁰ Predicted SM signal Predicted background Observed

W=Z!eX 0:520:05 0:370:03 0:006 0:0 ^0:3_0:0 0

W=Z!X 0:510:05 0:380:03 0:006 0:0 ^0:6_0:0 0

W=Z! 6E_TX 0:640:06 0:720:06 0:009 1:40:8 0

W=Z!jj 1:340:26 1:350:20 0:018 2:11:2 3

Total 3:010:28 2:820:21 0:039 3:5 ^1:6_1:5 3

221803-6 221803-6

[5] Pseudorapidityis defined as lntan%=2with% measured with respect to the incoming proton direction.

[6] D. Amidei et al., Nucl. Instrum. Methods Phys. Res., Sect. A350, 73 (1994); S. Cihangiret al., Nucl. Instrum.

Methods Phys. Res., Sect. A360, 137 (1995).

[7] G. Marchesini et al., Comput. Phys. Commun.67, 465 (1992).

[8] For a detailed accounting of lepton selection criteria suitable for the identification of vector boson decays at CDF see, for instance, T. Affolderet al., Phys. Rev. D64, 52001 (2001).

[9] G. Zech, Nucl. Instrum. Methods Phys. Res., Sect. A277, 608 (1989); O. Helene, Nucl. Instrum. Methods Phys.

Res.212, 319 (1983).