Electroweak Measurements in Electron-Positron Collisions at W-Boson-Pair Energies at LEP

arXiv:1302.3415v4 [hep-ex] 19 Sep 2013

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

CERN-PH-EP/2013-022 arXiv:1302.3415 [hep-ex] February 14th, 2013

Electroweak Measurements in

Electron-Positron Collisions

at W-Boson-Pair Energies at LEP

The ALEPH Collaboration

The DELPHI Collaboration

The L3 Collaboration

The OPAL Collaboration

The LEP Electroweak Working Group

Submitted to PHYSICS REPORTS

February 14th, 2013

Abstract

Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb−1_{collected by the four LEP experiments ALEPH,}

DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV.

Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron-positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose-Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, mW and ΓW, the

branching fraction of W decays to hadrons, B(W → had), and the trilinear gauge-boson self-couplings gZ

1, κγ and λγ are determined to be:

mW = 80.376 ± 0.033 GeV ΓW = 2.195 ± 0.083 GeV B(W → had) = 67.41 ± 0.27 % g₁Z = 0.984+0.018_−0.020 κγ = 0.982 ± 0.042 λγ = −0.022 ± 0.019 .

Keywords: Electron-positron physics, electroweak interactions, decays of heavy intermediate gauge bosons, fermion-antifermion production, precision measurements at W-pair energies, tests of the Standard Model, radiative corrections, effective coupling constants, neutral weak current, Z boson, W boson, top quark, Higgs boson.

Author Lists

The ALEPH, DELPHI, L3, OPAL collaborations have provided the inputs for the combined results presented in this Report. The LEP Electroweak Working Group has performed the combinations. The Working Group consists of members of the four LEP collaborations. The lists of authors from the collaborations follow.

The ALEPH Collaboration

S. Schael,1 _{R. Barate,}2 _{R. Bruneli`ere,}2 _{D. Buskulic,}2 _{I. De Bonis,}2 _{D. Decamp,}2 _{P. Ghez,}2 _{C. Goy,}2

S. J´ez´equel,2 _{J.-P. Lees,}2 _{A. Lucotte,}2 _{F. Martin,}2 _{E. Merle,}2 _{M.-N. Minard,}2 _{J.-Y. Nief,}2 _{P. Odier,}2

B. Pietrzyk,2 _{B. Trocm´e,}2 _{S. Bravo,}3 _{M.P. Casado,}3 _{M. Chmeissani,}3 _{P. Comas,}3 _{J.M. Crespo,}3

E. Fernandez,3 _{M. Fernandez-Bosman,}3 _{Ll. Garrido,}3,a15 _{E. Grauges,}3 _{A. Juste,}3 _{M. Martinez,}3

G. Merino,3 _{R. Miquel,}3 _{Ll.M. Mir,}3 _{S. Orteu,}3 _{A. Pacheco,}3 _{I.C. Park,}3 _{J. Perlas,}3 _{I. Riu,}3 _{H. Ruiz,}3

F. Sanchez,3 _{A. Colaleo,}4 _{D. Creanza,}4 _{N. De Filippis,}4 _{M. de Palma,}4 _{G. Iaselli,}4 _{G. Maggi,}4

M. Maggi,4 _{S. Nuzzo,}4 _{A. Ranieri,}4 _{G. Raso,}4,a24 _{F. Ruggieri,}4 _{G. Selvaggi,}4 _{L. Silvestris,}4

P. Tempesta,4 _{A. Tricomi,}4,a3 _{G. Zito,}4 _{X. Huang,}5 _{J. Lin,}5 _{Q. Ouyang,}5 _{T. Wang,}5 _{Y. Xie,}5 _{R. Xu,}5

S. Xue,5 _{J. Zhang,}5 _{L. Zhang,}5 _{W. Zhao,}5 _{D. Abbaneo,}6 _{A. Bazarko,}6 _{U. Becker,}6 _{G. Boix,}6,a33

F. Bird,6 _{E. Blucher,}6 _{B. Bonvicini,}6 _{P. Bright-Thomas,}6 _{T. Barklow,}6,a26 _{O. Buchm¨uller,}6,a26

M. Cattaneo,6 _{F. Cerutti,}6 _{V. Ciulli,}6 _{B. Clerbaux,}6,a23 _{H. Drevermann,}6 _{R.W. Forty,}6 _{M. Frank,}6

T.C. Greening,6 _{R. Hagelberg,}6 _{A.W. Halley,}6 _{F. Gianotti,}6 _{M. Girone,}6 _{J.B. Hansen,}6 _{J. Harvey,}6

R. Jacobsen,6 _{D.E. Hutchcroft,}6,a30 _{P. Janot,}6 _{B. Jost,}6 _{J. Knobloch,}6 _{M. Kado,}6,a2 _{I. Lehraus,}6

P. Lazeyras,6 _{P. Maley,}6 _{P. Mato,}6 _{J. May,}6 _{A. Moutoussi,}6 _{M. Pepe-Altarelli,}6 _{F. Ranjard,}6

L. Rolandi,6 _{D. Schlatter,}6 _{B. Schmitt,}6 _{O. Schneider,}6 _{W. Tejessy,}6 _{F. Teubert,}6 _{I.R. Tomalin,}6

E. Tournefier,6 _{R. Veenhof,}6 _{A. Valassi,}6 _{W. Wiedenmann,}6 _{A.E. Wright,}6 _{Z. Ajaltouni,}7

F. Badaud,7 _{G. Chazelle,}7 _{O. Deschamps,}7 _{S. Dessagne,}7 _{A. Falvard,}7,a20 _{C. Ferdi,}7 _{D. Fayolle,}7

P. Gay,7 _{C. Guicheney,}7 _{P. Henrard,}7 _{J. Jousset,}7 _{B. Michel,}7 _{S. Monteil,}7 _{J.C. Montret,}7 _{D. Pallin,}7

J.M. Pascolo,7 _{P. Perret,}7 _{F. Podlyski,}7 _{H. Bertelsen,}8 _{T. Fernley,}8 _{J.D. Hansen,}8 _{J.R. Hansen,}8

P.H. Hansen,8 _{A.C. Kraan,}8 _{A. Lindahl,}8 _{R. Mollerud,}8 _{B.S. Nilsson,}8 _{B. Rensch,}8 _{A. Waananen,}8

G. Daskalakis,9 _{A. Kyriakis,}9 _{C. Markou,}9 _{E. Simopoulou,}9 _{I. Siotis,}9 _{A. Vayaki,}9 _{K. Zachariadou,}9

A. Blondel,10,a12 _{G. Bonneaud,}10 _{J.-C. Brient,}10 _{F. Machefert,}10 _{A. Roug´e,}10 _{M. Rumpf,}10

M. Swynghedauw,10 _{R. Tanaka,}10 _{M. Verderi,}10 _{H. Videau,}10 _{V. Ciulli,}11 _{E. Focardi,}11 _{G. Parrini,}11

K. Zachariadou,11 _{M. Corden,}12 _{C. Georgiopoulos,}12 _{A. Antonelli,}13 _{M. Antonelli,}13

G. Bencivenni,13 _{G. Bologna,}13,a34 _{F. Bossi,}13 _{P. Campana,}13 _{G. Capon,}13 _{F. Cerutti,}13

V. Chiarella,13 _{G. Felici,}13 _{P. Laurelli,}13 _{G. Mannocchi,}13,a5 _{G.P. Murtas,}13 _{L. Passalacqua,}13

P. Picchi,13 _{P. Colrain,}14 _{I. ten Have,}14 _{I.S. Hughes,}14 _{J. Kennedy,}14 _{I.G. Knowles,}14 _{J.G. Lynch,}14

W.T. Morton,14 _{P. Negus,}14 _{V. O’Shea,}14 _{C. Raine,}14 _{P. Reeves,}14 _{J.M. Scarr,}14 _{K. Smith,}14

A.S. Thompson,14 _{R.M. Turnbull,}14 _{S. Wasserbaech,}15 _{O. Buchm¨uller,}16 _{R. Cavanaugh,}16,a4

A. Putzer,16 _{J. Sommer,}16 _{H. Stenzel,}16 _{K. Tittel,}16 _{W. Werner,}16 _{M. Wunsch,}16,a19 _{R. Beuselinck,}17

D.M. Binnie,17 _{W. Cameron,}17 _{G. Davies,}17 _{P.J. Dornan,}17 _{S. Goodsir,}17 _{N. Marinelli,}17

E.B Martin,17 _{J. Nash,}17 _{J. Nowell,}17 _{S.A. Rutherford,}17 _{J.K. Sedgbeer,}17 _{J.C. Thompson,}17,a14

R. White,17 _{M.D. Williams,}17 _{V.M. Ghete,}18 _{P. Girtler,}18 _{E. Kneringer,}18 _{D. Kuhn,}18

G. Rudolph,18 _{E. Bouhova-Thacker,}19 _{C.K. Bowdery,}19 _{P.G. Buck,}19 _{D.P. Clarke,}19 _{G. Ellis,}19

A.J. Finch,19 _{F. Foster,}19 _{G. Hughes,}19 _{R.W.L. Jones,}19 _{N.R. Keemer,}19 _{M.R. Pearson,}19

N.A. Robertson,19 _{T. Sloan,}19 _{M. Smizanska,}19 _{S.W. Snow,}19 _{M.I. Williams,}19 _{O. van der Aa,}20

C. Delaere,20,a28 _{G.Leibenguth,}20,a31 _{V. Lemaitre,}20,a29 _{L.A.T. Bauerdick,}21 _{U. Blumenschein,}21

P. van Gemmeren,21 _{I. Giehl,}21 _{F. H¨olldorfer,}21 _{K. Jakobs,}21 _{M. Kasemann,}21 _{F. Kayser,}21

K. Kleinknecht,21 _{A.-S. M¨uller,}21 _{G. Quast,}21 _{B. Renk,}21 _{E. Rohne,}21 _{H.-G. Sander,}21

S. Schmeling,21 _{H. Wachsmuth,}21 _{R. Wanke,}21 _{C. Zeitnitz,}21 _{T. Ziegler,}21 _{J.J. Aubert,}22

C. Benchouk,22 _{A. Bonissent,}22 _{J. Carr,}22 _{P. Coyle,}22 _{C. Curtil,}22 _{A. Ealet,}22 _{F. Etienne,}22

D. Fouchez,22 _{F. Motsch,}22 _{P. Payre,}22 _{D. Rousseau,}22 _{A. Tilquin,}22 _{M. Talby,}22 _{M.Thulasidas,}22

M. Aleppo,23 _{M. Antonelli,}23 _{F. Ragusa,}23 _{V. B¨uscher,}24 _{A. David,}24 _{H. Dietl,}24,a32 _{G. Ganis,}24,a27

K. H¨uttmann,24 _{G. L¨utjens,}24 _{C. Mannert,}24 _{W. M¨anner,}24,a32 _{H.-G. Moser,}24 _{R. Settles,}24

H. Seywerd,24 _{H. Stenzel,}24 _{M. Villegas,}24 _{W. Wiedenmann,}24 _{G. Wolf,}24 _{P. Azzurri,}25 _{J. Boucrot,}25

O. Callot,25 _{S. Chen,}25 _{A. Cordier,}25 _{M. Davier,}25 _{L. Duflot,}25 _{J.-F. Grivaz,}25 _{Ph. Heusse,}25

A. Jacholkowska,25,a6 _{F. Le Diberder,}25 _{J. Lefran¸cois,}25 _{A.M. Mutz,}25 _{M.H. Schune,}25 _{L. Serin,}25

J.-J. Veillet,25 _{I. Videau,}25 _{D. Zerwas,}25 _{P. Azzurri,}26 _{G. Bagliesi,}26 _{S. Bettarini,}26 _{T. Boccali,}26

C. Bozzi,26 _{G. Calderini,}26 _{R. Dell’Orso,}26 _{R. Fantechi,}26 _{I. Ferrante,}26 _{F. Fidecaro,}26 _{L. Fo`a,}26

A. Giammanco,26 _{A. Giassi,}26 _{A. Gregorio,}26 _{F. Ligabue,}26 _{A. Lusiani,}26 _{P.S. Marrocchesi,}26

A. Messineo,26 _{F. Palla,}26 _{G. Rizzo,}26 _{G. Sanguinetti,}26 _{A. Sciab`a,}26 _{G. Sguazzoni,}26 _{P. Spagnolo,}26

J. Steinberger,26 _{R. Tenchini,}26 _{C. Vannini,}26 _{A. Venturi,}26 _{P.G. Verdini,}26 _{O. Awunor,}27

G.A. Blair,27 _{G. Cowan,}27 _{A. Garcia-Bellido,}27 _{M.G. Green,}27 _{T. Medcalf,}27 _{A. Misiejuk,}27

J.A. Strong,27 _{P. Teixeira-Dias,}27 _{D.R. Botterill,}28 _{R.W. Clifft,}28 _{T.R. Edgecock,}28 _{M. Edwards,}28

S.J. Haywood,28 _{P.R. Norton,}28 _{I.R. Tomalin,}28 _{J.J. Ward,}28 _{B. Bloch-Devaux,}29 _{D. Boumediene,}29

P. Colas,29 _{S. Emery,}29 _{B. Fabbro,}29 _{W. Kozanecki,}29 _{E. Lan¸con,}29 _{M.-C. Lemaire,}29 _{E. Locci,}29

P. Perez,29 _{J. Rander,}29 _{J.F. Renardy,}29 _{A. Roussarie,}29 _{J.P. Schuller,}29 _{J. Schwindling,}29

B. Tuchming,29 _{B. Vallage,}29 _{S.N. Black,}30 _{J.H. Dann,}30 _{H.Y. Kim,}30 _{N. Konstantinidis,}30

A.M. Litke,30 _{M.A. McNeil,}30 _{G. Taylor,}30 _{C.N. Booth,}31 _{S. Cartwright,}31 _{F. Combley,}31,a25

P.N. Hodgson,31 _{M. Lehto,}31 _{L.F. Thompson,}31 _{K. Affholderbach,}32 _{E. Barberio,}32 _{A. B¨ohrer,}32

S. Brandt,32 _{H. Burkhardt,}32 _{E. Feigl,}32 _{C. Grupen,}32 _{J. Hess,}32 _{G. Lutters,}32 _{H. Meinhard,}32

J. Minguet-Rodriguez,32 _{L. Mirabito,}32 _{A. Misiejuk,}32 _{E. Neugebauer,}32 _{A. Ngac,}32 _{G. Prange,}32

F. Rivera,32 _{P. Saraiva,}32 _{U. Sch¨afer,}32 _{U. Sieler,}32 _{L. Smolik,}32 _{F. Stephan,}32 _{H. Trier,}32

M. Apollonio,33 _{C. Borean,}33 _{L. Bosisio,}33 _{R. Della Marina,}33 _{G. Giannini,}33 _{B. Gobbo,}33

G. Musolino,33 _{L. Pitis,}33 _{H. He,}34 _{H. Kim,}34 _{J. Putz,}34 _{J. Rothberg,}34 _{S.R. Armstrong,}35

L. Bellantoni,35 _{K. Berkelman,}35 _{D. Cinabro,}35 _{J.S. Conway,}35 _{K. Cranmer,}35 _{P. Elmer,}35 _{Z. Feng,}35

D.P.S. Ferguson,35 _{Y. Gao,}35,a13 _{S. Gonz´alez,}35 _{J. Grahl,}35 _{J.L. Harton,}35 _{O.J. Hayes,}35 _{H. Hu,}35

S. Jin,35 _{R.P. Johnson,}35 _{J. Kile,}35 _{P.A. McNamara III,}35 _{J. Nielsen,}35 _{W. Orejudos,}35 _{Y.B. Pan,}35

Y. Saadi,35 _{I.J. Scott,}35 _{V. Sharma,}35 _{A.M. Walsh,}35 _{J. Walsh,}35 _{J. Wear,}35

J.H. von Wimmersperg-Toeller,35 _{W. Wiedenmann,}35 _{J. Wu,}35 _{S.L. Wu,}35 _{X. Wu,}35

J.M. Yamartino,35 _{G. Zobernig,}35 _{G. Dissertori.}36

1 _{Physikalisches Institut der RWTH-Aachen, D-52056 Aachen, Germany} 2 _{Laboratoire de Physique des Particules (LAPP), IN}2_P3_{-CNRS, F-74019}

Annecy-le-Vieux Cedex, France

3 _{Institut de F´ısica d’Altes Energies, Universitat Aut`onoma de Barcelona, E-08193}

4 _{Dipartimento di Fisica, INFN Sezione di Bari, I-70126 Bari, Italy}

5 _{Institute of High Energy Physics, Academia Sinica, Beijing, The People’s Republic of}

Chinaa8

6 _{European Laboratory for Particle Physics (CERN), CH-1211 Geneva 23, Switzerland} 7 _{Laboratoire de Physique Corpusculaire, Universit´e Blaise Pascal, IN}2_P3_-CNRS,

Clermont-Ferrand, F-63177 Aubi`ere, France

8 _{Niels Bohr Institute, 2100 Copenhagen, DK-Denmark}a9

9 _{Nuclear Research Center Demokritos (NRCD), GR-15310 Attiki, Greece}

10 _{Laoratoire Leprince-Ringuet, Ecole Polytechnique, IN}2_P3_{-CNRS, F-91128 Palaiseau}

Cedex, France

11 _{Dipartimento di Fisica, Universit`a di Firenze, INFN Sezione di Firenze, I-50125 Firenze,}

Italy

12 _{Supercomputer Computations Research Institute, Florida State University, Tallahasee,}

FL-32306-4052, USA

13 _{Laboratori Nazionali dell’INFN (LNF-INFN), I-00044 Frascati, Italy}

14 _{Department of Physics and Astronomy, University of Glasgow, Glasgow G12}

8QQ,United Kingdoma10

15 _{Utah Valley State College, Orem, UT 84058, U.S.A.}

16 _{Kirchhoff-Institut f¨ur Physik, Universit¨at Heidelberg, D-69120 Heidelberg, Germany}a16 17 _{Department of Physics, Imperial College, London SW7 2BZ, United Kingdom}a10 18 _{Institut f¨ur Experimentalphysik, Universit¨at Innsbruck, A-6020 Innsbruck, Austria}a18 19 _{Department of Physics, University of Lancaster, Lancaster LA1 4YB, United}

Kingdoma10

20 _{Institut de Physique Nucl´eaire, D´epartement de Physique, Universit´e Catholique de}

Louvain, 1348 Louvain-la-Neuve, Belgium

21 _{Institut f¨ur Physik, Universit¨at Mainz, D-55099 Mainz, Germany}a16

22 _{Centre de Physique des Particules de Marseille, Univ M´editerran´ee, IN}2_P3_-CNRS,

F-13288 Marseille, France

23 _{Dipartimento di Fisica, Universit`a di Milano e INFN Sezione di Milano, I-20133 Milano,}

Italy.

24 _{Max-Planck-Institut f¨ur Physik, Werner-Heisenberg-Institut, D-80805 M¨unchen,}

Germanya16

25 _{Laboratoire de l’Acc´el´erateur Lin´eaire, Universit´e de Paris-Sud, IN}2_P3_{-CNRS, F-91898}

Orsay Cedex, France

26 _{Dipartimento di Fisica dell’Universit`a, INFN Sezione di Pisa, e Scuola Normale}

Superiore, I-56010 Pisa, Italy

27 _{Department of Physics, Royal Holloway & Bedford New College, University of London,}

Egham, Surrey TW20 OEX, United Kingdoma10

28 _{Particle Physics Dept., Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11}

OQX, United Kingdoma10

29 _{CEA, DAPNIA/Service de Physique des Particules, CE-Saclay, F-91191 Gif-sur-Yvette}

Cedex, Francea17

30 _{Institute for Particle Physics, University of California at Santa Cruz, Santa Cruz, CA}

95064, USAa22

31 _{Department of Physics, University of Sheffield, Sheffield S3 7RH, United Kingdom}a10 32 _{Fachbereich Physik, Universit¨at Siegen, D-57068 Siegen, Germany}a16

33 _{Dipartimento di Fisica, Universit`a di Trieste e INFN Sezione di Trieste, I-34127 Trieste,}

Italy

34 _{Experimental Elementary Particle Physics, University of Washington, Seattle, WA}

98195 U.S.A.

35 _{Department of Physics, University of Wisconsin, Madison, WI 53706, USA}a11 36 _{Institute for Particle Physics, ETH H¨onggerberg, 8093 Z¨urich, Switzerland.}

a1 _{Also at CERN, 1211 Geneva 23, Switzerland.}

a2 _{Now at Fermilab, PO Box 500, MS 352, Batavia, IL 60510, USA}

a3 _{Also at Dipartimento di Fisica di Catania and INFN Sezione di Catania, 95129 Catania,}

Italy.

a4 _{Now at University of Florida, Department of Physics, Gainesville, Florida 32611-8440,}

USA

a5 _{Also IFSI sezione di Torino, INAF, Italy.}

a6 _{Also at Groupe d’Astroparticules de Montpellier, Universit´e de Montpellier II, 34095,}

Montpellier, France.

a7 _{Supported by CICYT, Spain.}

a8 _{Supported by the National Science Foundation of China.} a9 _{Supported by the Danish Natural Science Research Council.}

a10 _{Supported by the UK Particle Physics and Astronomy Research Council.} a11 _{Supported by the US Department of Energy, grant DE-FG0295-ER40896.}

a12 _{Now at Departement de Physique Corpusculaire, Universit´e de Gen`eve, 1211 Gen`eve 4,}

Switzerland.

a13 _{Also at Department of Physics, Tsinghua University, Beijing, The People’s Republic of}

China.

a14 _{Supported by the Leverhulme Trust.}

a15 _{Permanent address: Universitat de Barcelona, 08208 Barcelona, Spain.} a16 _{Supported by Bundesministerium f¨ur Bildung und Forschung, Germany.} a17 _{Supported by the Direction des Sciences de la Mati`ere, C.E.A.}

a18 _{Supported by the Austrian Ministry for Science and Transport.} a19 _{Now at SAP AG, 69185 Walldorf, Germany}

a20 _{Now at Groupe d’ Astroparticules de Montpellier, Universit´e de Montpellier II, 34095}

Montpellier, France.

a21 _{Now at BNP Paribas, 60325 Frankfurt am Mainz, Germany}

a22 _{Supported by the US Department of Energy, grant DE-FG03-92ER40689.}

a23 _{Now at Institut Inter-universitaire des hautes Energies (IIHE), CP 230, Universit´e Libre}

de Bruxelles, 1050 Bruxelles, Belgique

a24 _{Now at Dipartimento di Fisica e Tecnologie Relative, Universit`a di Palermo, Palermo,}

Italy.

a25 _Deceased.

a26 _{Now at SLAC, Stanford, CA 94309, U.S.A} a27 _{Now at CERN, 1211 Geneva 23, Switzerland} a28 _{Research Fellow of the Belgium FNRS} a29 _{Research Associate of the Belgium FNRS}

a30 _{Now at Liverpool University, Liverpool L69 7ZE, United Kingdom}

a31 _{Supported by the Federal Office for Scientific, Technical and Cultural Affairs through}

a32 _{Now at Henryk Niewodnicznski Institute of Nuclear Physics, Polish Academy of}

Sciences, Cracow, Poland

a33 _{Supported by the Commission of the European Communities, contract}

ERBFMBICT982894

a34 _{Also Istituto di Fisica Generale, Universit`a di Torino, 10125 Torino, Italy}

The DELPHI Collaboration

J. Abdallah,27 _{P. Abreu,}24 _{W. Adam,}56 _{P. Adzic,}13 _{T. Albrecht,}19 _{R. Alemany-Fernandez,}10

T. Allmendinger,19 _{P.P. Allport,}25 _{U. Amaldi,}31 _{N. Amapane,}49 _{S. Amato,}53 _{E. Anashkin,}38

A. Andreazza,30 _{S. Andringa,}24 _{N. Anjos,}24 _{P. Antilogus,}27 _{W-D. Apel,}19 _{Y. Arnoud,}16 _{S. Ask,}10

B. Asman,48 _{J.E. Augustin,}27 _{A. Augustinus,}10 _{P. Baillon,}10 _{A. Ballestrero,}50 _{P. Bambade,}22

R. Barbier,29 _{D. Bardin,}18 _{G.J. Barker,}58 _{A. Baroncelli,}41 _{M. Battaglia,}10 _{M. Baubillier,}27

K-H. Becks,59 _{M. Begalli,}8 _{A. Behrmann,}59 _{K. Belous,}44 _{E. Ben-Haim,}27 _{N. Benekos,}34

A. Benvenuti,6 _{C. Berat,}16 _{M. Berggren,}27 _{L. Berntzon,}48 _{D. Bertrand,}3 _{M. Besancon,}42

N. Besson,42 _{D. Bloch,}11 _{M. Blom,}33 _{M. Bluj,}57 _{M. Bonesini,}31 _{M. Boonekamp,}42 _{P.S.L. Booth}†_,25

G. Borisov,23 _{O. Botner,}54 _{B. Bouquet,}22 _{T.J.V. Bowcock,}25 _{I. Boyko,}18 _{M. Bracko,}45 _{R. Brenner,}54

E. Brodet,37 _{P. Bruckman,}20 _{J.M. Brunet,}9 _{L. Bugge,}35 _{B. Buschbeck,}56 _{P. Buschmann,}59

M. Calvi,31 _{T. Camporesi,}10 _{V. Canale,}40 _{F. Carena,}10 _{N. Castro,}24 _{F. Cavallo,}6 _{M. Chapkin,}44

Ph. Charpentier,10 _{P. Checchia,}38 _{R. Chierici,}29 _{P. Chliapnikov,}44 _{J. Chudoba,}14 _{K. Cieslik,}20

P. Collins,10 _{R. Contri,}15 _{G. Cosme,}22 _{F. Cossutti,}51 _{M.J. Costa,}55 _{B. Crawley,}1 _{D. Crennell,}39

J. Cuevas,36 _{J. D’Hondt,}3 _{J. Dalmau,}48 _{T. da Silva,}53 _{W. Da Silva,}27 _{G. Della Ricca,}51

A. De Angelis,52 _{W. De Boer,}19 _{C. De Clercq,}3 _{B. De Lotto,}52 _{N. De Maria,}49 _{A. De Min,}38

L. de Paula,53 _{L. Di Ciaccio,}40 _{A. Di Simone,}40 _{K. Doroba,}57 _{J. Drees,}59 _{M. Dris,}34 _{A. Duperrin,}29

G. Eigen,5 _{T. Ekelof,}54 _{M. Ellert,}54 _{M. Elsing,}10 _{M.C. Espirito Santo,}24 _{G. Fanourakis,}13

D. Fassouliotis,13,4 _{M. Feindt,}19 _{J. Fernandez,}43 _{A. Ferrer,}55 _{F. Ferro,}15 _{U. Flagmeyer,}59 _{H. Foeth,}10

E. Fokitis,34 _{F. Fulda-Quenzer,}22 _{J. Fuster,}55 _{M. Gandelman,}53 _{C. Garcia,}55 _{Ph. Gavillet,}10

E. Gazis,34 _{D. Gele,}11 _{R. Gokieli}†_,57 _{B. Golob,}45,47 _{G. Gomez-Ceballos,}43 _{P. Gon¸calves,}24

E. Graziani,41 _{G. Grosdidier,}22 _{K. Grzelak,}57 _{J. Guy,}39 _{C. Haag,}19 _{A. Hallgren,}54 _{K. Hamacher,}59

K. Hamilton,37 _{S. Haug,}35 _{F. Hauler,}19 _{V. Hedberg,}28 _{M. Hennecke,}19 _{H. Herr}†_,10 _{J. Hoffman,}57

S-O. Holmgren,48 _{P.J. Holt,}10 _{M.A. Houlden,}25 _{K. Hultqvist,}48 _{J.N. Jackson,}25 _{G. Jarlskog,}28

P. Jarry,42 _{D. Jeans,}37 _{E.K. Johansson,}48 _{P.D. Johansson,}48 _{P. Jonsson,}29 _{C. Joram,}10

L. Jungermann,19 _{F. Kapusta,}27 _{S. Katsanevas,}29 _{E. Katsoufis,}34 _{G. Kernel,}45 _{B.P. Kersevan,}45,47

U. Kerzel,19 _{A. Kiiskinen,}17 _{B.T. King,}25 _{N.J. Kjaer,}10 _{P. Kluit,}33 _{P. Kokkinias,}13

V. Kostioukhine,15 _{C. Kourkoumelis,}4 _{O. Kouznetsov,}18 _{Z. Krumstein,}18 _{M. Kucharczyk,}20

J. Lamsa,1 _{G. Leder,}56 _{F. Ledroit,}16 _{L. Leinonen,}48 _{R. Leitner,}32 _{J. Lemonne,}3 _{V. Lepeltier}†_,22

T. Lesiak,20 _{J. Libby,}37 _{W. Liebig,}59 _{D. Liko,}56 _{A. Lipniacka,}5 _{J.H. Lopes,}53 _{J.M. Lopez,}36

D. Loukas,13 _{P. Lutz,}42 _{L. Lyons,}37 _{J. MacNaughton,}56 _{A. Malek,}59 _{S. Maltezos,}34 _{F. Mandl,}56

J. Marco,43 _{R. Marco,}43 _{B. Marechal,}53 _{M. Margoni,}38 _{J-C. Marin,}10 _{C. Mariotti,}10 _{A. Markou,}13

C. Martinez-Rivero,43 _{J. Masik,}14 _{N. Mastroyiannopoulos,}13 _{F. Matorras,}43 _{C. Matteuzzi,}31

F. Mazzucato,38 _{M. Mazzucato,}38 _{R. Mc Nulty,}25 _{C. Meroni,}30 _{W.T. Meyer,}1 _{E. Migliore,}49

W. Mitaroff,56 _{U. Mjoernmark,}28 _{T. Moa,}48 _{M. Moch,}19 _{K. Moenig,}12 _{R. Monge,}15 _{J. Montenegro,}33

D. Moraes,53 _{P. Morettini,}15 _{U. Mueller,}59 _{K. Muenich,}59 _{M. Mulders,}33 _{L. Mundim,}8 _{W. Murray,}39

B. Muryn,21 _{G. Myatt,}37 _{T. Myklebust,}35 _{M. Nassiakou,}13 _{F. Navarria,}6 _{K. Nawrocki,}57

S. Nemecek,14 _{R. Nicolaidou,}42 _{V. Nikolaenko,}11 _{M. Nikolenko,}18,11 _{A. Oblakowska-Mucha,}21

V. Obraztsov,44 _{A. Olshevski,}18 _{A. Onofre,}24 _{R. Orava,}17 _{K. Osterberg,}17 _{A. Ouraou,}42

L. Pape,10 _{C. Parkes,}26 _{F. Parodi,}15 _{U. Parzefall,}10 _{A. Passeri,}41 _{O. Passon,}59 _{V. Perepelitsa,}55

A. Perrotta,6 _{A. Petrolini,}15 _{J. Piedra,}43 _{L. Pieri,}38 _{F. Pierre}†_,42 _{M. Pimenta,}24 _{T. Podobnik,}45,47

V. Poireau,10 _{M.E. Pol,}7 _{G. Polok,}20 _{P. Poropat}†_,51 _{V. Pozdniakov,}18 _{N. Pukhaeva,}18 _{A. Pullia,}31

D. Radojicic,37 _{J. Rames,}14 _{L. Ramler,}19 _{A. Read,}35 _{P. Rebecchi,}10 _{J. Rehn,}19 _{D. Reid,}33

R. Reinhardt,59 _{P. Renton,}37 _{F. Richard,}22 _{J. Ridky,}14 _{I. Ripp-Baudot,}11 _{M. Rivero,}43

D. Rodriguez,43 _{A. Romero,}49 _{P. Ronchese,}38 _{E. Rosenberg,}1 _{P. Roudeau,}22 _{T. Rovelli,}6

V. Ruhlmann-Kleider,42 _{D. Ryabtchikov,}44 _{A. Sadovsky,}18 _{L. Salmi,}17 _{J. Salt,}55 _{C. Sander,}19

A. Savoy-Navarro,27 _{U. Schwickerath,}10 _{A. Segar}†_,37 _{R. Sekulin,}39 _{M. Siebel,}59 _{L. Simard,}42

A. Sisakian†_,18 _{G. Smadja,}29 _{O. Smirnova,}28 _{A. Sokolov,}44 _{A. Sopczak,}23 _{R. Sosnowski,}57

T. Spassov,10 _{M. Stanitzki,}19 _{A. Stocchi,}22 _{J. Strauss,}56 _{B. Stugu,}5 _{M. Szczekowski,}57

M. Szeptycka,57 _{T. Szumlak,}21 _{T. Tabarelli,}31 _{A.C. Taffard,}25 _{F. Tegenfeldt,}54 _{F. Terranova,}31

J. Thomas,37 _{J. Timmermans,}33 _{L. Tkatchev,}18 _{M. Tobin,}60 _{S. Todorovova,}14 _{B. Tom´e,}24

A. Tonazzo,31 _{P. Tortosa,}55 _{P. Travnicek,}14 _{D. Treille,}10 _{G. Tristram,}9 _{M. Trochimczuk,}57

C. Troncon,30 _{M-L. Turluer,}42 _{I.A. Tyapkin,}18 _{P. Tyapkin,}18 _{S. Tzamarias,}13 _{V. Uvarov,}44

G. Valenti,6 _{P. Van Dam,}33 _{J. Van Eldik,}10 _{A. Van Lysebetten,}3 _{N. van Remortel,}2

I. Van Vulpen,33 _{G. Vegni,}30 _{F. Veloso,}24 _{W. Venus,}39 _{F. Verbeure}†_,2 _{P. Verdier,}29 _{V. Verzi,}40

D. Vilanova,42 _{L. Vitale,}51 _{V. Vrba,}14 _{H. Wahlen,}59 _{A.J. Washbrook,}25 _{C. Weiser,}19 _{D. Wicke,}59

J. Wickens,3 _{G. Wilkinson,}37 _{M. Winter,}11 _{M. Witek,}20 _{O. Yushchenko,}44 _{A. Zalewska,}20

P. Zalewski,57 _{D. Zavrtanik,}46 _{V. Zhuravlov,}18 _{N.I. Zimin,}18 _{A. Zintchenko,}18 _{M. Zupan.}13 1 _{Department of Physics and Astronomy, Iowa State University, Ames IA 50011-3160,}

USA

2 _{Physics Department, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen,}

Belgium

3 _{IIHE, ULB-VUB, Pleinlaan 2, B-1050 Brussels, Belgium}

4 _{Physics Laboratory, University of Athens, Solonos Str. 104, GR-10680 Athens, Greece} 5 _{Department of Physics, University of Bergen, All´egaten 55, NO-5007 Bergen, Norway} 6 _{Dipartimento di Fisica, Universit`a di Bologna and INFN, Viale C. Berti Pichat 6/2,}

IT-40127 Bologna, Italy

7 _{Centro Brasileiro de Pesquisas F´ısicas, rua Xavier Sigaud 150, BR-22290 Rio de Janeiro,}

Brazil

8 _{Inst. de F´ısica, Univ. Estadual do Rio de Janeiro, rua S˜ao Francisco Xavier 524, Rio de}

Janeiro, Brazil

9 _{Coll`ege de France, Lab. de Physique Corpusculaire, IN2P3-CNRS, FR-75231 Paris}

Cedex 05, France

10 _{CERN, CH-1211 Geneva 23, Switzerland}

11 _{Institut Pluridisciplinaire Hubert Curien, Universit´e de Strasbourg, IN2P3-CNRS,}

BP28, FR-67037 Strasbourg Cedex 2, France

12 _{Now at DESY-Zeuthen, Platanenallee 6, D-15735 Zeuthen, Germany}

13 _{Institute of Nuclear Physics, N.C.S.R. Demokritos, P.O. Box 60228, GR-15310 Athens,}

Greece

14 _{FZU, Inst. of Phys. of the C.A.S. High Energy Physics Division, Na Slovance 2, CZ-182}

21, Praha 8, Czech Republic

15 _{Dipartimento di Fisica, Universit`a di Genova and INFN, Via Dodecaneso 33, IT-16146}

Genova, Italy

16 _{Laboratoire de Physique Subatomique et de Cosmologie, Universit´e Joseph Fourier}

Grenoble 1, CNRS/IN2P3, Institut Polytechnique de Grenoble, FR-38026 Grenoble Cedex, France

17 _{Helsinki Institute of Physics and Department of Physics, P.O. Box 64, FIN-00014}

University of Helsinki, Finland

18 _{Joint Institute for Nuclear Research, Dubna, Head Post Office, P.O. Box 79, RU-101 000}

Moscow, Russian Federation

19 _{Institut f¨ur Experimentelle Kernphysik, Universit¨at Karlsruhe, Postfach 6980, DE-76128}

Karlsruhe, Germany

20 _{Institute of Nuclear Physics PAN,Ul. Radzikowskiego 152, PL-31142 Krakow, Poland} 21 _{Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy,}

PL-30055 Krakow, Poland

22 _{LAL, Univ Paris-Sud, CNRS/IN2P3, Orsay, France}

23 _{School of Physics and Chemistry, University of Lancaster, Lancaster LA1 4YB, UK} 24 _{LIP, IST, FCUL - Av. Elias Garcia, 14-1}o_{, PT-1000 Lisboa Codex, Portugal}

25 _{Department of Physics, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK} 26 _{Dept. of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow G12}

8QQ, UK

27 _{LPNHE, IN2P3-CNRS, Univ. Paris VI et VII, 4 place Jussieu, FR-75252 Paris Cedex}

05, France

28 _{Department of Physics, University of Lund, S¨olvegatan 14, SE-223 63 Lund, Sweden} 29 _{Universit´e Claude Bernard de Lyon, IPNL, IN2P3-CNRS, FR-69622 Villeurbanne}

Cedex, France

30 _{Dipartimento di Fisica, Universit`a di Milano and INFN-MILANO, Via Celoria 16,}

IT-20133 Milan, Italy

31 _{Dipartimento di Fisica, Univ. di Milano-Bicocca and INFN-MILANO, Piazza della}

Scienza 3, IT-20126 Milan, Italy

32 _{IPNP of MFF, Charles Univ., Areal MFF, V Holesovickach 2, CZ-180 00, Praha 8,}

Czech Republic

33 _{NIKHEF, Postbus 41882, NL-1009 DB Amsterdam, The Netherlands}

34 _{National Technical University, Physics Department, Zografou Campus, GR-15773}

Athens, Greece

35 _{Physics Department, University of Oslo, Blindern, NO-0316 Oslo, Norway} 36 _{Dpto. Fisica, Univ. Oviedo, Avda. Calvo Sotelo s/n, ES-33007 Oviedo, Spain} 37 _{Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK} 38 _{Dipartimento di Fisica, Universit`a di Padova and INFN, Via Marzolo 8, IT-35131}

Padua, Italy

39 _{Rutherford Appleton Laboratory, Chilton, Didcot OX11 OQX, UK}

40 _{Dipartimento di Fisica, Universit`a di Roma II and INFN, Tor Vergata, IT-00173 Rome,}

Italy

41 _{Dipartimento di Fisica, Universit`a di Roma III and INFN, Via della Vasca Navale 84,}

IT-00146 Rome, Italy

42 _{DAPNIA/Service de Physique des Particules, CEA-Saclay, FR-91191 Gif-sur-Yvette}

Cedex, France

43 _{Instituto de Fisica de Cantabria (CSIC-UC), Avda. los Castros s/n, ES-39006}

Santander, Spain

44 _{Institute for high energy physics, 142281 Protvino, Moscow region, Russian Federation} 45 _{J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia}

46 _{Laboratory for Astroparticle Physics, University of Nova Gorica, Kostanjeviska 16a,}

47 _{Department of Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia} 48 _{Fysikum, Stockholm University, Box 6730, SE-113 85 Stockholm, Sweden}

49 _{Dipartimento di Fisica Sperimentale, Universit`a di Torino and INFN, Via P. Giuria 1,}

IT-10125 Turin, Italy

50 _{INFN,Sezione di Torino and Dipartimento di Fisica Teorica, Universit`a di Torino, Via}

Giuria 1, IT-10125 Turin, Italy

51 _{Dipartimento di Fisica, Universit`a di Trieste and INFN, Via A. Valerio 2, IT-34127}

Trieste, Italy

52 _{Istituto di Fisica, Universit`a di Udine and INFN, IT-33100 Udine, Italy} 53 _{Univ. Federal do Rio de Janeiro, C.P. 68528 Cidade Univ., Ilha do Fund˜ao}

BR-21945-970 Rio de Janeiro, Brazil

54 _{Department of Radiation Sciences, University of Uppsala, P.O. Box 535, SE-751 21}

Uppsala, Sweden

55 _{IFIC, Valencia-CSIC, and D.F.A.M.N., U. de Valencia, Avda. Dr. Moliner 50, ES-46100}

Burjassot (Valencia), Spain

56 _{Institut f¨ur Hochenergiephysik, ¨Osterr. Akad. d. Wissensch., Nikolsdorfergasse 18,}

AT-1050 Vienna, Austria

57 _{Inst. Nuclear Studies and University of Warsaw, Ul. Hoza 69, PL-00681 Warsaw, Poland} 58 _{Now at University of Warwick, Coventry CV4 7AL, UK}

59 _{Fachbereich Physik, University of Wuppertal, Postfach 100 127, DE-42097 Wuppertal,}

Germany

60 _{Now at Physik-Institut der Universit¨at Z¨urich, Z¨urich, Switzerland} † _Deceased

The L3 Collaboration

P.Achard,20 _O.Adriani,17 _{M.Aguilar-Benitez,}25 _J.Alcaraz,25 _G.Alemanni,23 _J.Allaby,18 _A.Aloisio,29

M.G.Alviggi,29 _H.Anderhub,49 _V.P.Andreev,6,34 _F.Anselmo,8 _A.Arefiev,28 _T.Azemoon,3 _T.Aziz,9

P.Bagnaia,39 _A.Bajo,25 _G.Baksay,26 _L.Baksay,26 _S.V.Baldew,2 _S.Banerjee,9 _Sw.Banerjee,4

A.Barczyk,49,47 _{R.Barill`ere,}18 _P.Bartalini,23 _M.Basile,8 _N.Batalova,46 _R.Battiston,33 _A.Bay,23

U.Becker,13 _F.Behner,49 _L.Bellucci,17 _R.Berbeco,3 _J.Berdugo,25 _P.Berges,13 _B.Bertucci,33

B.L.Betev,49 _M.Biasini,33 _M.Biglietti,29 _A.Biland,49 _{J.J.Blaising,}4 _S.C.Blyth,35 _G.J.Bobbink,2

A.B¨ohm,1 _L.Boldizsar,12 _B.Borgia,39 _S.Bottai,17 _D.Bourilkov,49 _M.Bourquin,20 _S.Braccini,20

J.G.Branson,41 _F.Brochu,4 _J.D.Burger,13 _W.J.Burger,33 _X.D.Cai,13 _M.Capell,13 _{G.Cara Romeo,}8

G.Carlino,29 _A.Cartacci,17 _J.Casaus,25 _F.Cavallari,39 _N.Cavallo,36 _C.Cecchi,33 _M.Cerrada,25

M.Chamizo,20 _Y.H.Chang,44 _M.Chemarin,24 _A.Chen,44 _G.Chen,7 _G.M.Chen,7 _H.F.Chen,22

H.S.Chen,7 _G.Chiefari,29 _L.Cifarelli,40 _F.Cindolo,8 _I.Clare,13 _R.Clare,38 _G.Coignet,4 _N.Colino,25

S.Costantini,39 _{B.de la Cruz,}25 _{S.Cucciarelli,}33 _{R.de Asmundis,}29 _P.D´eglon,20 _{J.Debreczeni,}12

A.Degr´e,4 _K.Dehmelt,26 _K.Deiters,47 _{D.della Volpe,}29 _E.Delmeire,20 _P.Denes,37

F.DeNotaristefani,39 _{A.De Salvo,}49 _M.Diemoz,39 _{M.Dierckxsens,}2 _C.Dionisi,39 _M.Dittmar,49

A.Doria,29 _M.T.Dova,10,♯ _{D.Duchesneau,}4 _M.Duda,1 _B.Echenard,20 _A.Eline,18 _{A.El Hage,}1

H.El Mamouni,24 _A.Engler,35 _F.J.Eppling,13 _P.Extermann,20 _M.A.Falagan,25 _S.Falciano,39

A.Favara,32 _J.Fay,24 _O.Fedin,34 _M.Felcini,49 _T.Ferguson,35 _H.Fesefeldt,1 _E.Fiandrini,33 _J.H.Field,20

F.Filthaut,31 _P.H.Fisher,13 _W.Fisher,37 _G.Forconi,13 _{K.Freudenreich,}49 _C.Furetta,27

Yu.Galaktionov,28,13 _S.N.Ganguli,9 _{P.Garcia-Abia,}25 _M.Gataullin,32 _S.Gentile,39 _S.Giagu,39

Z.F.Gong,22 _G.Grenier,24 _O.Grimm,49 _{M.W.Gruenewald,}16 _V.K.Gupta,37 _A.Gurtu,9 _L.J.Gutay,46

G.Holzner,49 _S.R.Hou,44 _B.N.Jin,7 _P.Jindal,14 _L.W.Jones,3 _{P.de Jong,}2 _{I.Josa-Mutuberr´ıa,}25

M.Kaur,14 _{M.N.Kienzle-Focacci,}20 _J.K.Kim,43 _J.Kirkby,18 _W.Kittel,31 _A.Klimentov,13,28

A.C.K¨onig,31 _M.Kopal,46 _V.Koutsenko,13,28 _M.Kr¨aber,49 _R.W.Kraemer,35 _A.Kr¨uger,48 _A.Kunin,13

P.Ladron de Guevara,25 _I.Laktineh,24 _G.Landi,17 _M.Lebeau,18 _A.Lebedev,13 _P.Lebrun,24

P.Lecomte,49 _P.Lecoq,18 _{P.Le Coultre,}49 _{J.M.Le Goff,}18 _R.Leiste,48 _{M.Levtchenko,}27

P.Levtchenko,34 _C.Li,22 _S.Likhoded,48 _C.H.Lin,44 _W.T.Lin,44 _F.L.Linde,2 _L.Lista,29 _Z.A.Liu,7

W.Lohmann,48 _E.Longo,39 _Y.S.Lu,7 _C.Luci,39 _L.Luminari,39 _{W.Lustermann,}49 _W.G.Ma,22

L.Malgeri,18 _A.Malinin,28 _C.Ma˜na,25 _J.Mans,37 _J.P.Martin,24 _F.Marzano,39 _K.Mazumdar,9

R.R.McNeil,6 _S.Mele,18,29 _L.Merola,29 _M.Meschini,17 _W.J.Metzger,31 _A.Mihul,11 _H.Milcent,18

G.Mirabelli,39 _J.Mnich,1 _G.B.Mohanty,9 _G.S.Muanza,24 _A.J.M.Muijs,2 _M.Musy,39 _S.Nagy,15

S.Natale,20 _{M.Napolitano,}29 _{F.Nessi-Tedaldi,}49 _H.Newman,32 _A.Nisati,39 _T.Novak,31 _H.Nowak,48

R.Ofierzynski,49 _G.Organtini,39 _I.Pal,46_C.Palomares,25 _P.Paolucci,29 _R.Paramatti,39 _G.Passaleva,17

S.Patricelli,29 _T.Paul,10 _M.Pauluzzi,33 _C.Paus,13 _F.Pauss,49 _M.Pedace,39 _S.Pensotti,27

D.Perret-Gallix,4 _D.Piccolo,29 _F.Pierella,8 _M.Pieri,41 _M.Pioppi,33 _{P.A.Pirou´e,}37 _E.Pistolesi,27

V.Plyaskin,28 _M.Pohl,20 _V.Pojidaev,17 _J.Pothier,18 _D.Prokofiev,34 _{G.Rahal-Callot,}49

M.A.Rahaman,9 _P.Raics,15 _N.Raja,9 _R.Ramelli,49 _{P.G.Rancoita,}27 _R.Ranieri,17 _A.Raspereza,48

P.Razis,30 _S.Rembeczki,26 _D.Ren,49 _M.Rescigno,39 _S.Reucroft,10 _S.Riemann,48 _K.Riles,3 _B.P.Roe,3

L.Romero,25 _A.Rosca,48 _C.Rosemann,1 _{C.Rosenbleck,}1 _{S.Rosier-Lees,}4 _S.Roth,1 _J.A.Rubio,18

G.Ruggiero,17 _{H.Rykaczewski,}49 _A.Sakharov,49 _S.Saremi,6 _S.Sarkar,39 _J.Salicio,18 _E.Sanchez,25

C.Sch¨afer,18 _{V.Schegelsky,}34 _H.Schopper,21 _{D.J.Schotanus,}31 _C.Sciacca,29 _L.Servoli,33

S.Shevchenko,32 _N.Shivarov,42 _V.Shoutko,13 _E.Shumilov,28 _A.Shvorob,32 _D.Son,43 _C.Souga,24

P.Spillantini,17 _M.Steuer,13 _{D.P.Stickland,}37 _B.Stoyanov,42 _{A.Straessner,}20 _K.Sudhakar,9

G.Sultanov,42 _L.Z.Sun,22 _S.Sushkov,1 _H.Suter,49 _J.D.Swain,10 _Z.Szillasi,26,¶ _X.W.Tang,7 _P.Tarjan,15

L.Tauscher,5 _L.Taylor,10 _B.Tellili,24 _D.Teyssier,24 _{C.Timmermans,}31 _S.C.C.Ting,13 _S.M.Ting,13

S.C.Tonwar,9 _J.T´oth,12 _C.Tully,37 _K.L.Tung,7_J.Ulbricht,49 _E.Valente,39 _{R.T.Van de Walle,}31

R.Vasquez,46 _{G.Vesztergombi,}12 _I.Vetlitsky,28 _G.Viertel,49 _M.Vivargent,4 _S.Vlachos,5

I.Vodopianov,26 _H.Vogel,35 _H.Vogt,48 _I.Vorobiev,35,28 _{A.A.Vorobyov,}34 _M.Wadhwa,5 _Q.Wang31

X.L.Wang,22 _Z.M.Wang,22 _M.Weber,18 _S.Wynhoff,37,† _L.Xia,32 _Z.Z.Xu,22 _J.Yamamoto,3

B.Z.Yang,22 _C.G.Yang,7 _H.J.Yang,3 _M.Yang,7 _S.C.Yeh,45 _An.Zalite,34 _Yu.Zalite,34 _Z.P.Zhang,22

J.Zhao,22 _G.Y.Zhu,7 _R.Y.Zhu,32 _H.L.Zhuang,7 _A.Zichichi,8,18,19 _{B.Zimmermann,}49 _M.Z¨oller.1 1 _{III. Physikalisches Institut, RWTH, D-52056 Aachen, Germany}§

2 _{National Institute for High Energy Physics, NIKHEF, and University of Amsterdam,}

NL-1009 DB Amsterdam, The Netherlands

3 _{University of Michigan, Ann Arbor, MI 48109, USA}

4 _{Laboratoire d’Annecy-le-Vieux de Physique des Particules, LAPP,IN2P3-CNRS, BP}

110, F-74941 Annecy-le-Vieux CEDEX, France

5 _{Institute of Physics, University of Basel, CH-4056 Basel, Switzerland} 6 _{Louisiana State University, Baton Rouge, LA 70803, USA}

7 _{Institute of High Energy Physics, IHEP, 100039 Beijing, China}△

8 _{University of Bologna and INFN-Sezione di Bologna, I-40126 Bologna, Italy} 9 _{Tata Institute of Fundamental Research, Mumbai (Bombay) 400 005, India} 10 _{Northeastern University, Boston, MA 02115, USA}

11 _{Institute of Atomic Physics and University of Bucharest, R-76900 Bucharest, Romania} 12 _{Central Research Institute for Physics of the Hungarian Academy of Sciences, H-1525}

Budapest 114, Hungary‡

13 _{Massachusetts Institute of Technology, Cambridge, MA 02139, USA} 14 _{Panjab University, Chandigarh 160 014, India}

15 _{KLTE-ATOMKI, H-4010 Debrecen, Hungary}¶

16 _{UCD School of Physics, University College Dublin, Belfield, Dublin 4, Ireland} 17 _{INFN Sezione di Firenze and University of Florence, I-50125 Florence, Italy}

18 _{European Laboratory for Particle Physics, CERN, CH-1211 Geneva 23, Switzerland} 19 _{World Laboratory, FBLJA Project, CH-1211 Geneva 23, Switzerland}

20 _{University of Geneva, CH-1211 Geneva 4, Switzerland} 21 _{University of Hamburg, D-22761 Hamburg, Germany}

22 _{Chinese University of Science and Technology, USTC, Hefei, Anhui 230 029, China}△ 23 _{University of Lausanne, CH-1015 Lausanne, Switzerland}

24 _{Institut de Physique Nucl´eaire de Lyon, IN2P3-CNRS,Universit´e Claude Bernard,}

F-69622 Villeurbanne, France

25 _{Centro de Investigaciones Energ´eticas, Medioambientales y Tecnol´ogicas, CIEMAT,}

E-28040 Madrid, Spain♭

26 _{Florida Institute of Technology, Melbourne, FL 32901, USA} 27 _{INFN-Sezione di Milano, I-20133 Milan, Italy}

28 _{Institute of Theoretical and Experimental Physics, ITEP, Moscow, Russia} 29 _{INFN-Sezione di Napoli and University of Naples, I-80125 Naples, Italy} 30 _{Department of Physics, University of Cyprus, Nicosia, Cyprus}

31 _{Radboud University and NIKHEF, NL-6525 ED Nijmegen, The Netherlands} 32 _{California Institute of Technology, Pasadena, CA 91125, USA}

33 _{INFN-Sezione di Perugia and Universit`a Degli Studi di Perugia, I-06100 Perugia, Italy} 34 _{Nuclear Physics Institute, St. Petersburg, Russia}

35 _{Carnegie Mellon University, Pittsburgh, PA 15213, USA}

36 _{INFN-Sezione di Napoli and University of Potenza, I-85100 Potenza, Italy} 37 _{Princeton University, Princeton, NJ 08544, USA}

38 _{University of Californa, Riverside, CA 92521, USA}

39 _{INFN-Sezione di Roma and University of Rome, “La Sapienza”, I-00185 Rome, Italy} 40 _{University and INFN, Salerno, I-84100 Salerno, Italy}

41 _{University of California, San Diego, CA 92093, USA}

42 _{Bulgarian Academy of Sciences, Central Lab. of Mechatronics and Instrumentation,}

BU-1113 Sofia, Bulgaria

43 _{The Center for High Energy Physics, Kyungpook National University, 702-701 Taegu,}

Republic of Korea

44 _{National Central University, Chung-Li, Taiwan, China}

45 _{Department of Physics, National Tsing Hua University, Taiwan, China} 46 _{Purdue University, West Lafayette, IN 47907, USA}

47 _{Paul Scherrer Institut, PSI, CH-5232 Villigen, Switzerland} 48 _{DESY, D-15738 Zeuthen, Germany}

49 _{Eidgen¨ossische Technische Hochschule, ETH Z¨urich, CH-8093 Z¨urich, Switzerland}

§ _{Supported by the German Bundesministerium f¨ur Bildung, Wissenschaft, Forschung}

und Technologie.

‡ _{Supported by the Hungarian OTKA fund under contract numbers T019181, F023259}

and T037350.

¶ _{Also supported by the Hungarian OTKA fund under contract number T026178.} ♭ _{Supported also by the Comisi´on Interministerial de Ciencia y Tecnolog´ıa.}

Plata, Argentina.

△ _{Supported by the National Natural Science Foundation of China.} † _Deceased.

The OPAL Collaboration

G. Abbiendi2_{, K. Ackerstaff}7_{, C. Ainsley}5_{, P.F. ˚Akesson}7_{, G. Alexander}21_{, J. Allison}15_{, N. Altekamp}5_,

K. Ametewee25_{, G. Anagnostou}1_{, K.J. Anderson}8_{, S. Anderson}11_{, S. Arcelli}2_{, S. Asai}22_{, S.F. Ashby}1_,

D. Axen26_{, G. Azuelos}17_{, A.H. Ball}7_{, I. Bailey}25_{, E. Barberio}7,p_{, T. Barillari}31_{, R.J. Barlow}15_{, R. Bartoldus}3_,

R.J. Batley5_{, S. Baumann}3_{, P. Bechtle}24_{, J. Bechtluft}13_{, C. Beeston}15_{, T. Behnke}24_{, K.W. Bell}19_,

P.J. Bell1_{, G. Bella}21_{, A. Bellerive}6_{, G. Benelli}4_{, S. Bentvelsen}7,aa_{, P. Berlich}9_{, S. Bethke}31_{, O. Biebel}30_,

O. Boeriu9_{, V. Blobel}24_{, I.J. Bloodworth}1_{, J.E. Bloomer}1_{, M. Bobinski}9_{, P. Bock}10_{, O. Boeriu}9_,

D. Bonacorsi2_{, H.M. Bosch}10_{, M. Boutemeur}30_{, B.T. Bouwens}11_{, S. Braibant}2_{, P. Bright-Thomas}1_,

L. Brigliadori2_{, R.M. Brown}19_{, H.J. Burckhart}7_{, C. Burgard}7_{, R. B¨urgin}9_{, J. Cammin}3_{, S. Campana}4_,

P. Capiluppi2_{, R.K. Carnegie}6_{, A.A. Carter}12_{, J.R. Carter}5_{, C.Y. Chang}16_{, D.G. Charlton}1_{, D. Chrisman}4_,

C. Ciocca2_{, P.E.L. Clarke}14,bb_{, E. Clay}14_{, I. Cohen}21_{, J.E. Conboy}14_{, O.C. Cooke}15_{, J. Couchman}14_,

C. Couyoumtzelis12_{, R.L. Coxe}8_{, A. Csilling}28_{, M. Cuffiani}2_{, S. Dado}20_{, C. Dallapiccola}16_{, M. Dallavalle}2_,

S. Dallison15_{, S. De Jong}11,cc_{, A. De Roeck}7_{, P. Dervan}14_{, E.A. De Wolf}7,s_{, L.A. del Pozo}7_{, K. Desch}24_,

B. Dienes29_{, M.S. Dixit}6_{, E. do Couto e Silva}11_{, M. Donkers}6_{, M. Doucet}17_{, J. Dubbert}30_{, E. Duchovni}23_,

G. Duckeck30_{, I.P. Duerdoth}15_{, J.E.G. Edwards}15_{, P.G. Estabrooks}6_{, E. Etzion}21_{, H.G. Evans}8,dd_,

M. Evans12_{, F. Fabbri}2_{, M. Fanti}2_{, P. Fath}10_{, L. Feld}9_{, P. Ferrari}7_{, F. Fiedler}30_{, M. Fierro}2_{, H.M. Fischer}3_,

I. Fleck9_{, R. Folman}23,kk_{, D.G. Fong}16_{, M. Ford}15_{, M. Foucher}17_{, A. Frey}7_{, A. F¨urtjes}7_{, D.I. Futyan}15_,

P. Gagnon11_{, J.W. Gary}4_{, J. Gascon}17_{, S.M. Gascon-Shotkin}16,ee_{, G. Gaycken}24_{, N.I. Geddes}19_,

C. Geich-Gimbel3_{, T. Geralis}19_{, G. Giacomelli}2_{, P. Giacomelli}2_{, R. Giacomelli}2_{, V. Gibson}5_{, W.R. Gibson}12_,

D.M. Gingrich27_{, M. Giunta}4_{, D. Glenzinski}8,f f_{, J. Goldberg}20_{, M.J. Goodrick}5_{, W. Gorn}4_{, K. Graham}25_,

C. Grandi2_{, E. Gross}23_{, J. Grunhaus}21_{, M. Gruw´e}7_{, P.O. G¨unther}3_{, A. Gupta}8_{, C. Hajdu}28_{, M. Hamann}24_,

G.G. Hanson4_{, M. Hansroul}7_{, M. Hapke}12_{, K. Harder}24_{, A. Harel}20_{, C.K. Hargrove}6_{, M.}

Harin-Dirac4_{, P.A. Hart}8_{, C. Hartmann}3_{, A. Hauke}3_{, M. Hauschild}7_{, C.M. Hawkes}1_{, R. Hawkings}7_{, R.J. Hemingway}

C. Hensel24_{, M. Herndon}16_{, G. Herten}9_{, R.D. Heuer}24,y_{, M.D. Hildreth}7,gg_{, J.C. Hill}5_{, S.J. Hillier}1_,

T. Hilse9_{, P.R. Hobson}33_{, A. Hocker}8_{, K. Hoffman}7_{, R.J. Homer}1_{, A.K. Honma}7_{, D. Horv´ath}28,c_,

K.R. Hossain27_{, R. Howard}26_{, R.E. Hughes-Jones}15_{, P. H¨untemeyer}24_{, D.E. Hutchcroft}5_{, P.}

Igo-Kemenes10_{, D.C. Imrie}25_{, M.R. Ingram}15_{, K. Ishii}22_{, F.R. Jacob}19_{, A. Jawahery}16_{, P.W. Jeffreys}19_,

H. Jeremie17_{, M. Jimack}1_{, A. Joly}17_{, C.R. Jones}5_{, G. Jones}15_{, M. Jones}6_{, R.W.L. Jones}7,hh_{, U. Jost}10_,

P. Jovanovic1_{, T.R. Junk}6,i_{, N. Kanaya}22_{, J. Kanzaki}22,u_{, G. Karapetian}17_{, D. Karlen}25_{, V. Kartvelishvili}15_,

K. Kawagoe22_{, T. Kawamoto}22_{, R.K. Keeler}25_{, R.G. Kellogg}16_{, B.W. Kennedy}19_{, D.H. Kim}18_,

B.J. King7_{, J. Kirk}26_{, K. Klein}10_{, A. Klier}23_{, S. Kluth}31_{, T. Kobayashi}22_{, M. Kobel}3,t_{, D.S. Koetke}6_,

T.P. Kokott3_{, M. Kolrep}9_{, S. Komamiya}22_{, R.V. Kowalewski}25_{, T. Kr¨amer}24_{, A. Krasznahorkay Jr.}29,e_,

T. Kress10_{, P. Krieger}6,l_{, J. von Krogh}10_{, T. Kuhl}24_{, M. Kupper}23_{, P. Kyberd}12_{, G.D. Lafferty}15_,

R. Lahmann16_{, W.P. Lai}18_{, H. Landsman}20_{, D. Lanske}13,∗_{, J. Lauber}14_{, S.R. Lautenschlager}34_,

I. Lawson25_{, J.G. Layter}4_{, D. Lazic}20_{, A.M. Lee}34_{, E. Lefebvre}17_{, A. Leins}30_{, D. Lellouch}23_{, J. Letts}o_,

L. Levinson23_{, C. Lewis}14_{, R. Liebisch}10_{, J. Lillich}9_{, B. List}24_{, J. List}24_{, C. Littlewood}5_{, A.W. Lloyd}1_,

S.L. Lloyd12_{, F.K. Loebinger}15_{, G.D. Long}16_{, M.J. Losty}6,∗_{, J. Lu}26,b_{, A. Ludwig}3,t_{, J. Ludwig}9_,

A. Macchiolo17_{, A. Macpherson}27,y_{, W. Mader}3,t_{, M. Mannelli}7_{, S. Marcellini}2_{, T.E. Marchant}15_,

C. Markus3_{, A.J. Martin}12_{, J.P. Martin}17_{, G. Martinez}16_{, T. Mashimo}22_{, W. Matthews}25_{, P. M¨attig}23,m_,

W.J. McDonald27_{, J. McKenna}26_{, E.A. Mckigney}14_{, T.J. McMahon}1_{, A.I. McNab}12_{, R.A. McPherson}25_,

P. Mendez-Lorenzo30_{, F. Meijers}7_{, W. Menges}24_{, S. Menke}3_{, F.S. Merritt}8_{, H. Mes}6,a_{, N. Meyer}24_,

T. Mori22_{, M. Morii}22,jj_{, U. M¨uller}3_{, A. Mutter}9_{, K. Nagai}12_{, I. Nakamura}22,v_{, H. Nanjo}22_{, H.A. Neal}32_,

B. Nellen3_{, B. Nijjhar}15_{, R. Nisius}31_{, S.W. O’Neale}1,∗_{, F.G. Oakham}6_{, F. Odorici}2_{, H.O. Ogren}11_,

A. Oh7_{, A. Okpara}10_{, N.J. Oldershaw}15_{, T. Omori}22_{, M.J. Oreglia}8_{, S. Orito}22,∗_{, C. Pahl}31_{, J. P´alink´as}29_,

G. P´asztor4,g_{, J.R. Pater}15_{, G.N. Patrick}19_{, J. Patt}9_{, M.J. Pearce}1_{, S. Petzold}24_{, P. Pfeifenschneider}13,∗_,

J.E. Pilcher8_{, J. Pinfold}27_{, D.E. Plane}7_{, P. Poffenberger}25_{, J. Polok}7_{, B. Poli}2_{, O. Pooth}13_{, A. Posthaus}3_,

M. Przybycie´n7,n_{, H. Przysiezniak}27_{, A. Quadt}31_{, K. Rabbertz}7,r_{, D.L. Rees}1_{, C. Rembser}7_{, P. Renkel}23_,

H. Rick4_{, D. Rigby}1_{, S. Robertson}25_{, S.A. Robins}12_{, N. Rodning}27_{, J.M. Roney}25_{, A. Rooke}14_,

E. Ros7_{, S. Rosati}3_{, K. Roscoe}15_{, A.M. Rossi}2_{, M. Rosvick}25_{, P. Routenburg}27_{, Y. Rozen}20_{, K. Runge}9_,

O. Runolfsson7_{, U. Ruppel}13_{, D.R. Rust}11_{, R. Rylko}25_{, K. Sachs}6_{, T. Saeki}22_{, O. Sahr}30_{, E.K.G. Sarkisyan}7,j_,

M. Sasaki22_{, C. Sbarra}2_{, A.D. Schaile}30_{, O. Schaile}30_{, P. Scharff-Hansen}7_{, P. Schenk}24_{, J. Schieck}31_,

B. Schmitt7_{, S. Schmitt}10_{, T. Sch¨orner-Sadenius}7,z_{, M. Schr¨oder}7_{, H.C. Schultz-Coulon}9_{, M. Schulz}7_,

M. Schumacher3_{, P. Sch¨utz}3_{, C. Schwick}7_{, W.G. Scott}19_{, R. Seuster}13,f_{, T.G. Shears}7,h_{, B.C. Shen}4,∗_,

C.H. Shepherd-Themistocleous19_{, P. Sherwood}14_{, G.P. Siroli}2_{, A. Sittler}24_{, A. Skillman}14_{, A. Skuja}16_,

A.M. Smith7_{, T.J. Smith}25_{, G.A. Snow}16,∗_{, R. Sobie}25_{, S. S¨oldner-Rembold}15_{, S. Spagnolo}19_{, F. Spano}8,x_,

R.W. Springer27_{, M. Sproston}19_{, A. Stahl}13_{, M. Steiert}10_{, K. Stephens}15_{, J. Steuerer}24_{, B. Stockhausen}3_,

K. Stoll9_{, D. Strom}18_{, R. Str¨ohmer}30_{, F. Strumia}7_{, L. Stumpf}25_{, B. Surrow}7_{, P. Szymanski}19_{, R. Tafirout}17_,

S.D. Talbot1_{, S. Tanaka}22_{, P. Taras}17_{, S. Tarem}20_{, R.J. Taylor}14_{, M. Tasevsky}7,d_{, R. Teuscher}8_,

M. Thiergen9_{, J. Thomas}14_{, M.A. Thomson}5_{, E. von T¨orne}3_{, E. Torrence}18_{, S. Towers}6_{, D. Toya}22_,

T. Trefzger30_{, I. Trigger}7,w_{, Z. Tr´ocs´anyi}29,e_{, T. Tsukamoto}22_{, E. Tsur}21_{, A.S. Turcot}8_{, M.F.}

Turner-Watson1_{, I. Ueda}22_{, B. Ujv´ari}29,e_{, P. Utzat}10_{, B. Vachon25, R. Van Kooten}11_{, P. Vannerem}9_{, R. V´ertesi}29,e_,

M. Verzocchi16_{, P. Vikas}17_{, M. Vincter}25_{, E.H. Vokurka}15_{, C.F. Vollmer}30_{, H. Voss}7,q_{, J. Vossebeld}7,h_,

F. W¨ackerle9_{, A. Wagner}24_{, D. Waller}6_{, C.P. Ward}5_{, D.R. Ward}5_{, J.J. Ward}14_{, P.M. Watkins}1_,

A.T. Watson1_{, N.K. Watson}1_{, P.S. Wells}7_{, T. Wengler}7_{, N. Wermes}3_{, D. Wetterling}10_{J.S. White}25_,

B. Wilkens9_{, G.W. Wilson}15,k_{, J.A. Wilson}1_{, G. Wolf}23_{, S. Wotton}5_{, T.R. Wyatt}15_{, S. Yamashita}22_,

G. Yekutieli23_{, V. Zacek}17_{, D. Zer-Zion}4_{, L. Zivkovic}20

1_{School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK} 2_{Dipartimento di Fisica dell’ Universit`a di Bologna and INFN, I-40126 Bologna, Italy}

3_{Physikalisches Institut, Universit¨at Bonn, D-53115 Bonn, Germany}

4_{Department of Physics, University of California, Riverside CA 92521, USA} 5_{Cavendish Laboratory, Cambridge CB3 0HE, UK}

6_{Ottawa-Carleton Institute for Physics, Department of Physics, Carleton University, Ottawa,}

Ontario K1S 5B6, Canada

7_{CERN, European Organisation for Nuclear Research, CH-1211 Geneva 23, Switzerland} 8_{Enrico Fermi Institute and Department of Physics, University of Chicago, Chicago IL 60637,}

USA

9_{Fakult¨at f¨ur Physik, Albert-Ludwigs-Universit¨at Freiburg, D-79104 Freiburg, Germany} 10_{Physikalisches Institut, Universit¨at Heidelberg, D-69120 Heidelberg, Germany}

11_{Indiana University, Department of Physics, Bloomington IN 47405, USA}

12_{Queen Mary and Westfield College, University of London, London E1 4NS, UK}

13_{Technische Hochschule Aachen, III Physikalisches Institut, Sommerfeldstrasse 26-28, D-52056}

Aachen, Germany

14_{University College London, London WC1E 6BT, UK}

15_{School of Physics and Astronomy, Schuster Laboratory, The University of Manchester M13}

9PL, UK

16_{Department of Physics, University of Maryland, College Park, MD 20742, USA}

17_{Laboratoire de Physique Nucl´eaire, Universit´e de Montr´eal, Montr´eal, Qu´ebec H3C 3J7,}

18_{University of Oregon, Department of Physics, Eugene OR 97403, USA}

19_{Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK} 20_{Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel} 21_{Department of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel}

22_{International Centre for Elementary Particle Physics and Department of Physics, University}

of Tokyo, Tokyo 113-0033, and Kobe University, Kobe 657-8501, Japan

23_{Particle Physics Department, Weizmann Institute of Science, Rehovot 76100, Israel}

24_{Universit¨at Hamburg/DESY, Institut f¨ur Experimentalphysik, Notkestrasse 85, D-22607}

Ham-burg, Germany

25_{University of Victoria, Department of Physics, P O Box 3055, Victoria BC V8W 3P6, Canada} 26_{University of British Columbia, Department of Physics, Vancouver BC V6T 1Z1, Canada} 27_{University of Alberta, Department of Physics, Edmonton AB T6G 2J1, Canada}

28_{Research Institute for Particle and Nuclear Physics, H-1525 Budapest, P O Box 49, Hungary} 29_{Institute of Nuclear Research, H-4001 Debrecen, P O Box 51, Hungary}

30_{Ludwig-Maximilians-Universit¨at M¨unchen, Sektion Physik, Am Coulombwall 1, D-85748}

Garching, Germany

31_{Max-Planck-Institute f¨ur Physik, F¨ohringer Ring 6, D-80805 M¨unchen, Germany} 32_{Yale University, Department of Physics, New Haven, CT 06520, USA}

33_{Brunel University, Uxbridge, Middlesex UB8 3PH, UK}

34_{Duke University, Dept of Physics, Durham, NC 27708-0305, USA} a _{and at TRIUMF, Vancouver, Canada V6T 2A3}

b _{now at University of Alberta}

c _{and Institute of Nuclear Research, Debrecen, Hungary}

d _{now at Institute of Physics, Academy of Sciences of the Czech Republic 18221 Prague, Czech}

Republic

e _{and Department of Experimental Physics, University of Debrecen, Hungary} f _{and MPI M¨unchen}

g _{and Research Institute for Particle and Nuclear Physics, Budapest, Hungary} h _{now at University of Liverpool, Dept of Physics, Liverpool L69 3BX, U.K.} i _{now at Fermilab, Illinois, U.S.A.}

j _{and University of Texas at Arlington, USA}

k _{now at University of Kansas, Dept of Physics and Astronomy, Lawrence, KS 66045, U.S.A.} l _{now at University of Toronto, Dept of Physics, Toronto, Canada}

m _{current address Bergische Universit¨at, Wuppertal, Germany} n _{now at University of Mining and Metallurgy, Cracow, Poland} o _{now at University of California, San Diego, U.S.A.}

p _{now at The University of Melbourne, Victoria, Australia}

q _{now at IPHE Universit´e de Lausanne, CH-1015 Lausanne, Switzerland} r _{now at IEKP Universit¨at Karlsruhe, Germany}

s_{now at University of Antwerpen, Physics Department,B-2610 Antwerpen, Belgium; supported}

by Interuniversity Attraction Poles Programme – Belgian Science Policy

t _{now at Technische Universit¨at, Dresden, Germany}

u _{and High Energy Accelerator Research Organisation (KEK), Tsukuba, Ibaraki, Japan} v _{now at University of Pennsylvania, Philadelphia, Pennsylvania, USA}

w _{now at TRIUMF, Vancouver, Canada} x _{now at Columbia University}

aa _{now at Nikhef, the Netherlands}

bb _{now at University of Edinburgh, United Kingdom} cc _{now at University of Nijmegen, the Netherlands} dd _{now at Indiana University, USA}

ee _{now at IPN Lyon, France} f f _{now at Fermilab, USA}

gg _{now at University of Notre Dame, USA}

hh _{now at University of Lancaster, United Kingdom} ii _{now at Technion, Haifa, Israel}

jj _{now at Harvard University, USA}

kk _{now at Ben-Gurion University of the Negev, Beersheba, Israel} ∗ _Deceased

In addition to the support staff at our own institutions we are pleased to acknowledge the Department of Energy, USA,

National Science Foundation, USA,

Particle Physics and Astronomy Research Council, UK, Natural Sciences and Engineering Research Council, Canada,

Israel Science Foundation, administered by the Israel Academy of Science and Humanities, Benoziyo Center for High Energy Physics,

Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and a grant under the MEXT International Science Research Program,

Japanese Society for the Promotion of Science (JSPS), German Israeli Bi-national Science Foundation (GIF), Bundesministerium f¨ur Bildung und Forschung, Germany, National Research Council of Canada,

Hungarian Foundation for Scientific Research, OTKA T-038240, and T-042864, The NWO/NATO Fund for Scientific Research, the Netherlands.

Contents

2.3.1 QED Born Cross-Section . . . 27

2.3.2 Non-QED Models . . . 27

2.3.3 Radiative Corrections . . . 29

2.3.4 Theory Uncertainty . . . 29

2.4 Combination of the Differential Cross-Section . . . 30

2.5 Combined Total Cross-Section . . . 31

2.6 Interpretation . . . 31

2.7 Conclusion . . . 37

3 Fermion-Pair Production 39 3.1 Introduction . . . 39

3.2 Averages for Cross-Sections and Asymmetries . . . 40

3.3 Differential Cross-Sections for Muon- and Tau-Pair Final States . . . 43

3.4 Differential Cross-Sections for Electron-Positron Final States . . . 48

3.5 Interpretation . . . 53

3.5.1 Models with Z′ _{Bosons . . . 53}

3.5.2 Contact Interactions . . . 58

3.5.3 Large Extra Dimensions . . . 61

3.5.4 Leptoquarks . . . 64

3.6 Summary . . . 64

4 Final-State Interconnection Effects 66 4.1 Colour Reconnection . . . 66

4.1.1 Introduction . . . 66

4.1.2 Particle-Flow Measurements . . . 67

4.1.3 Determination of CR Effects Using W Mass Estimators . . . 70

4.1.4 Combination of LEP CR Measurements . . . 73

4.1.5 Summary . . . 74

4.2 Bose-Einstein Correlations . . . 74

4.2.2 Methods . . . 76

4.2.3 Distributions . . . 76

4.2.4 Results . . . 78

4.2.5 Conclusions . . . 80

5 Boson-Pair and Four-Fermion Processes 86 5.1 Introduction and Signal Definitions . . . 86

5.2 W-Pair Production . . . 88

5.2.1 Total Cross-Section Measurement . . . 89

5.2.2 Derived Quantities . . . 93

5.2.3 W Angular Distribution . . . 96

5.3 Z-Pair Production . . . 97

5.4 Z-γ∗ _{Production . . . 100}

5.5 Single-Boson Production . . . 100

5.5.1 Weν Cross-Section Measurement . . . 105

5.5.2 Zee Cross-Section Measurement . . . 105

5.6 WWγ Production . . . 112

5.7 Summary . . . 112

6 Electroweak Gauge Boson Self Couplings 114 6.1 Introduction . . . 114

6.1.1 Charged Triple Gauge Boson Couplings . . . 114

6.1.2 Neutral Triple Gauge Boson Couplings . . . 115

6.2 Combination Procedure . . . 116

6.3 Measurements . . . 118

6.4 Results . . . 119

6.4.1 Charged Triple Gauge Boson Couplings . . . 119

6.4.2 Neutral Triple Gauge Boson Couplings . . . 121

6.5 Summary and Conclusions . . . 127

7 Mass and Width of the W Boson 128 7.1 Introduction . . . 128

7.2 Determination of the W Mass at the W-Pair Production Threshold . . . 128

7.3 Measurement of Mass and Width by Direct Reconstruction . . . 129

7.3.1 Mass Reconstruction . . . 129

7.3.2 Kinematic Fitting . . . 130

7.3.3 Techniques for Determining the W-Boson Mass and Width . . . 131

7.3.4 Combination Procedure . . . 133

7.3.5 Overview of Systematic Uncertainties . . . 134

7.4 LEP Combined W-Boson Mass . . . 139

7.5 Consistency Checks . . . 140

7.6 LEP Combined W-Boson Width . . . 140

7.7 Summary . . . 141

8 Summary and Conclusions 145

A S-Matrix 147

A.1 Introduction . . . 147

A.2 The S-Matrix Ansatz . . . 148

A.3 LEP-I Combination . . . 149

A.4 Discussion . . . 150

A.5 S-Matrix Combination Tables . . . 157

B Two-Fermion Combination Details 162 B.1 Input Measurements . . . 163

B.2 Differential Cross-Section for Muon- and Tau-Pair Final States . . . 174

B.3 Differential Cross-Section for Electron-Positron Final States . . . 178

C Determination of the LEP Centre-of-Mass Energy Using Radiative-Return Events 181 D Tests of the Colour-Reconnection Combination Procedure 186 E Detailed Inputs and Results of LEP Four-Fermion Averages 191 F Constraints on the Standard Model 211 F.1 Introduction . . . 211

F.2 Measurements . . . 211

F.3 Theoretical Uncertainties . . . 214

Chapter 1

Introduction

The electron-positron collider LEP at CERN increased its collision centre-of-mass energy, √s, from the Z pole (LEP-I) up to 209 GeV during its second running phase (LEP-II) from 1995 to 2000. The four LEP experiments ALEPH, DELPHI, L3 and OPAL collected a combined total integrated luminosity of about 3 fb−1 _{in the LEP-II centre-of-mass energy range above the Z}

pole, 130 GeV to 209 GeV. This large data set explores the new energy regime accessed by LEP-II with high precision, allowing new tests of the electroweak Standard Model of particle physics [1] (SM), and searches for new physics effects at higher mass scales.

Combinations of electroweak measurements performed in electron-positron collisions at Z-pole centre-of-mass energies, at LEP-I and the SLC, are reported in Reference [4]. Here, the measurements in the electroweak sector of the SM at LEP-II centre-of-mass energies are dis-cussed, including, where necessary, studies of strong-interaction effects. Photon-pair, fermion-pair and four-fermion production processes are analysed and the results are presented in the form of total and differential cross-sections. Final-state interactions between the decay products in W-boson pair production are investigated for signals of colour reconnection and Bose-Einstein correlations. Pair-production of W bosons yields measurements of the mass, total decay width and decay branching fractions of the W boson. Together with other reactions such as single-W, single-Z, WWγ, Z-pair, Zγ and Zγγ production, the data sample allows stringent tests of the non-Abelian structure of the electroweak gauge group, by measuring triple and quartic electroweak gauge boson couplings.

1.1

LEP-II Data

In a circular accelerator such as LEP, the energy loss of the beam particles due to synchrotron radiation increases with the fourth power of the Lorentz γ factor. In order to push the LEP centre-of-mass energy beyond the Z-pole, the warm copper RF cavities used at LEP-I were replaced by superconducting RF cavities to increase the available RF power. In parallel the LEP-II centre-of-mass energy increased in steps up to a maximum of 209 GeV, reached in 2000, the final year of LEP operation. The centre-of-mass energies and the corresponding integrated luminosities collected per experiment are reported in Table 1.1. For some of the analyses described in this report, the data have been combined in different slices of centre-of-mass energies. About 0.75 fb−1 _{of integrated luminosity was recorded by each LEP experiment,}