Article

Search for a new weakly interacting particle

Laboratoire de Physique des Particules (LAPP), IN2P3-CNRS, F-74019 Annecy-le-Vieux Cedex, France; R. Alemany,; J.M. Crespo,; M. Delfino,; E. Fernandez,; V. Gaitan,; Ll. Garrido,; P. Mato,; Mir Ll.M.,; A. Pacheco; Laboratorio de Fisica de Altas Energias, Universidad Autonoma de Barcelona, E-08193 Bellaterra Barcelona, Spain; M.G. Catanesi,; D. Creanza,; M. de Palma,; A. Farilla,; G. Maggi,; M. Maggi,; S. Natali,; S. Nuzzo,; M. Quattromini,; A. Ranieri,; G. Raso,; F. Romano,; F. Ruggieri,; G. Selvaggi,; L. Silvestris,; P. Tempesta,; G. Zito; INFN, Sezione di Bari and Dipartamento di Fisica dell'Università, I-70126 Bari, Italy; Y. Gao,; D. Huang,; X. Huang,; J. Lin,; J. Lou,; T. Wang,; Y. Xie,; D. Xu,; R. Xu,; J. Zhang,; W. Zhao; Institute of High-Energy Physics, Academia Sinica, Beijing, China; F. Bird,; E. Blucher,; G. Bonvicini,; F. Bossi,; D. Brown,; H. Drevermann,; F. Dydak,; R.W. Forty,; C. Grab,; R. Hagelberg,; S. Haywood,; J. Hilgart,; B. Jost,; M. Kasemann,; J. Knobloch,; A. Lacourt,; E. Lançon,; I. Lehraus,; T. Lohse,; A. Marchioro,; M. Martinez,; S. Menary,; A. Minten,; A. Miotto,; R. Miguel,; H.-G. Moser,; J. Nash,; P. Palazzi,; F. Ranjard,; G. Redlinger,; A. Roth,; H. Rotscheidt,; R. St. Denis,; D. Schlatter,; M. Takashima,; W. Tejessy,; H. Wachsmuth,; S. Wasserbaech,; S. Wheeler,; W. Wiedenmann,; W. Witzeling,; J. Wotschack; European Laboratory for Particle Physics (CERN), CH-1211 Geneva 23, Switzerland; Z. Ajaltouni,; M. Bardadin-Otwinowska,; A. Falvard,; R. El Fellous,; P. Gay,; J. Harvey,; P. Henrard,; J. Jousset,; B. Michel,; J.-C. Montret,; D. Pallin,; P. Perret,; J. Proriol,; F. Prulhière,; G. Stimpfl; Laboratoire de Physique Corpusculaire, Université Blaise Pascal, Clermont-Ferrand, F-63177 Aubi`ere, France; J.D. Hansen,; J.R. Hansen,; P.H. Hansen,; R. Møllerud,; E.R. Nielsen,; B.S. Nilsson; Niels Bohr Institute, DK-2100 Copenhagen, Denmark; I. Efthymiopoulos,; E. Simopoulou,; A. Vayaki; Nuclear Research Center Demokritos (NRCD), Athens, Greece; J. Badier,; A. Blondel,; G. Bonneaud,; J. Bourotte,; F. Braems,; J.C. Brient,; G. Fouque,; A. Gamess,; R. Guirlet,; S. Orteu,; A. Rosowsky,; A. Rougé,; M. Rumpf,; R. Tanaka,; H. Videau; Laboratoire de Physique Nucléaire et des Hautes Energies, Ecole Polytechnique, IN2P3-CNRS, F-91128 Palaiseau Cedex, France; D.J. Candlin,; E. Veitch; Department of Physics, University of Edinburgh, Edinburgh EH9 3JZ, UK; G. Parrini; Dipartimento di Fisica, Università di Firenze and INFN Sezione di Firenze, I-50125 Florence, Italy; M. Corden,; C. Georgiopoulos,; M. Ikeda,; J. Lannutti,; M. Mermikides,; L. Sawyer; Supercomputer Computations Research Institute and Department of Physics, Florida State University, Tallahassee, FL 32306, USA; A. Antonelli,; R. Baldini,; G. Bencivenni,; P. Campana,; G. Capon,; V. Chiarella,; G. Felici,; P. Laurelli,; F. Murtas,; G.P. Murtas,; G. Nicoletti,; L. Passalacqua,; M. Pepe-Altarelli,; P. Zografou; Laboratori Nazionali dell'INFN (LNF-INFN), I-00044 Frascati, Italy; B. Altoon,; O. Boyle,; A.W. Halley,; I. ten Have,; J.L. Hearns,; J.G. Lynch,; W.T. Morton,; C. Raine,; J.M. Scarr,; K. Smith,; A.S. Thompson,; R.M. Turnbull; Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK; B. Brandl,; O. Braun,; R. Geiges,; C. Geweniger,; P. Hanke,; V. Hepp,; E.E. Kluge,; Y. Maumary,; A. Putzer,; B. Rensch,; A. Stahl,; K. Tittel,; M. Wunsch; Institut für Hochenergiephysik, Universität Heidelberg, W-6900 Heidelberg, FRG; A.T. Belk,; R. Beuselinck,; D.M. Binnie,; W. Cameron,; M. Cattaneo,; S. Dugeay,; A.M. Greene,; J.F. Hassard,; N.M. Lieske,; S.J. Patton,; D.G. Payne,; M.J. Phillips,; J.K. Sedgbeer,; G. Taylor,; I.R. Tomalin,; A.G. Wright; Department of Physics, Imperial College, London SW7 2BZ, UK; P. Girtler,; D. Kuhn,; G. Rudolph; Institut für Experimentalphysik, Universität Innsbruck, A-6020 Innsbruck, Austria; T.J. Brodbeck,; A.J. Finch,; F. Foster,; G. Hughes,; N.R. Keemer,; M. Nuttall,; A. Patel,; B.S. Rowlingson,; T. Sloan,; S.W. Snow,; E.P. Whelan; Department of Physics, University of Lancaster, Lancaster LA1 4YB, UK; T. Barczewski,; L.A.T. Bauerdick,; K. Kleinknecht,; B. Renk,; S. Roehn,; H.-G. Sander,; M. Schmelling,; H. Schmidt,; F. Steeg; Institut für Physik, Universität Mainz, W-6500 Mainz, FRG; J.-P. Albanese,; J.-J. Aubert,; C. Benchouk,; V. Bernard,; A. Bonissent,; D. Courvoisier,; F. Etienne,; S. Papalexiou,; P. Payre,; B. Pietrzyk,; Z. Qian; Centre de Physique des Particules, Faculté des Sciences de Luminy, IN2P3-CNRS, F-13288 Marseille, France; H. Becker,; W. Blum,; P. Cattaneo,; G. Cowan,; B. Dehning,; H. Dietl,; M. Fernandez-Bosman,; A. Jahn,; E. Lange,; J. Lauber,; G. Lütjens,; G. Lutz,; W. Männer,; Y. Pan,; R. Richter,; J. Schröder,; A.S. Schwarz,; R. Settles,; U. Stierlin,; J. Thomas,; G. Wolf; Max-Planck-Institut für Physik und Astrophysik, Werner-Heisenberg-Institut für Physik, W-8000 Munich, FRG; V. Bertin,; J. Boucrot,; X. Chen,; A. Cordier,; M. Davier,; G. Ganis,; J.-F. Grivaz,; Ph. Heusse,; P. Janot,; F. Le Diberder,; A.-M. Lutz,; J.-J. Veillet,; I. Videau,; Z. Zhang,; F. Zomer; Laboratoire de l'Accélérateur Linéaire, Université de Paris-Sud, IN2P3-CNRS, F-91405 Orsay Cedex, France; S.R. Amendolia,; G. Bagliesi,; G. Batignani,; L. Bosisio,; U. Bottigli,; C. Bradaschia,; M. Carpinelli,; M.A. Ciocci,; R. Dell'Orso,; I. Ferrante,; F. Fidecaro,; L. Foà,; E. Focardi,; F. Forti,; A. Giassi,; M.A. Giorgi,; F. Ligabue,; A. Lusiani,; E.B. Mannelli,; P.S. Marrocchesi,; A. Messineo,; L. Moneta,; F. Palla,; G. Sanguinetti,; J. Steinberger,; R. Tenchini,; G. Tonelli,; G. Triggiani,; C. Vannini,; A. Venturi,; P.G. Verdini,; J. Walsh; Dipartimento di Fisica dell' Università, INFN Sezione di Pisa, and Scuola Normale Superiore, I-56010 Pisa, Italy; J.M. Carter,; M.G. Green,; P.V. March,; T. Medcalf,; I.S. Quazi,; M.R. Saich,; J.A. Strong,; R.M. Thomas,; L.R. West,; T. Wildish; Department of Physics, Royal Holloway & Bedford New College, University of London, Surrey TW20 0EX, UK; D.R. Botterill,; R.W. Clifft,; T.R. Edgecock,; M. Edwards,; S.M. Fisher,; T.J. Jones,; P.R. Norton,; D.P. Salmon,; J.C. Thompson; Particle Physics Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK; B. Bloch-Devaux,; P. Colas,; C. Klopfenstein,; E. Locci,; S. Loucatos,; E. Monnier,; P. Perez,; J.A. Perlas,; F. Perrier,; J. Rander,; J.-F. Renardy,; A. Roussarie,; J.-P. Schuller,; J. Schwindling,; B. Vallage; Département de Physique des Particules Elémentaires, CEN-Saclay, F-91191 Gif-sur-Yvette Cedex, France; J.G. Ashman,; C.N. Booth,; C. Buttar,; R. Carney,; S. Cartwright,; F. Combley,; M. Dinsdale,; M. Dogru,; F. Hatfield,; J. Martin,; D. Parker,; P. Reeves,; L.F. Thompson; Department of Physics, University of Sheffield, Sheffield S3 7RH, UK; S. Brandt,; H. Burkhardt,; C. Grupen,; H. Meinhard,; L. Mirabito,; E. Neugebauer,; U. Schäfer,; H. Seywerd; Fachbereich Physik, Universität Siegen, W-5900 Siegen, FRG; G. Apollinari,; G. Giannini,; B. Gobbo,; F. Liello,; L. Rolandi,; U. Stiegler; Dipartimento di Fisica, Università di Trieste and INFN Sezione di Trieste, I-34127 Trieste, Italy; L. Bellantoni,; J.F. Boudreau,; D. Cinabro,; J.S. Conway,; A.J. DeWeerd,; Z. Feng,; D.P.S. Ferguson,; Y.S. Gao,; J. Grahl,; J.L. Harton,; J.E. Jacobsen,; R.P. Johnson,; B.W. LeClaire,; Y.B. Pan,; J.R. Pater,; Y. Saadi,; V. Sharma,; A.M. Walsh,; J.A. Wear,; F.V. Weber,; M.H. Whitney,; Sau Lan Wu,; Z.L. Zhou,; G. Zobernig; Department of Physics, University of Wisconsin, Madison, WI 53706, USA
Physics Letters B 01/1991; DOI: 10.1016/0370-2693(91)90657-C

ABSTRACT A search for events of the type e+e−→ℓ+ℓ−X0, where X0 can be any weakly interacting particle which couples to the Z, has been performed with the ALEPH detector at LEP, by searching for acollinear lepton pairs. Such particles can be excluded up to a mass of 7.0 GeV/c2 for a value of the ratio of branching fractions, Br(Z→X0l+l−)/Br(Z→l+l−), greater than 2.5 × 10−3 if the X0 has third component of isospin, I3 greater than and decays to a pair of virtual gauge bosons. When this analysis is combined with the previous results of the Higgs particle searches from ALEPH, this limit can be extended to an X0 mass of 60 GeV/c2.

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