Eur. Phys. J. C (2007) 50: 507-518
https://doi.org/10.1140/epjc/s10052-007-0273-z

Regular Article - Experimental Physics

Search for a fourth generation b’-quark at LEP-II at 196–209 GeV

¹ Department of Physics and Astronomy, Iowa State University, Ames, AI, 50011-3160, USA
² IIHE, ULB-VUB, Pleinlaan 2, 1050, Brussels, Belgium
³ Physics Laboratory, University of Athens, Solonos Str. 104, 10680, Athens, Greece
⁴ Department of Physics, University of Bergen, Allégaten 55, 5007, Bergen, Norway
⁵ Dipartimento di Fisica, Università di Bologna and INFN, Via Irnerio 46, 40126, Bologna, Italy
⁶ Centro Brasileiro de Pesquisas Físicas, rua Xavier Sigaud 150, 22290, Rio de Janeiro, Brazil
⁷ Inst. de Física, Univ. Estadual do Rio de Janeiro, rua São Francisco Xavier 524, Rio de Janeiro, Brazil
⁸ Lab. de Physique Corpusculaire, IN2P3-CNRS, Collège de France, 75231, Paris Cedex 05, France
⁹ CERN, 1211, Geneva 23, Switzerland
¹⁰ Institut de Recherches Subatomiques, IN2P3 - CNRS/ULP - BP20, 67037, Strasbourg Cedex, France
¹¹ DESY-Zeuthen, Platanenallee 6, 15735, Zeuthen, Germany
¹² Institute of Nuclear Physics, N.C.S.R. Demokritos, P.O. Box 60228, 15310, Athens, Greece
¹³ Inst. of Phys. of the C.A.S. High Energy Physics Division, FZU, Na Slovance 2, 18040, Praha 8, Czech Republic
¹⁴ Dipartimento di Fisica, Università di Genova and INFN, Via Dodecaneso 33, 16146, Genova, Italy
¹⁵ Institut des Sciences Nucléaires, IN2P3-CNRS, Université de Grenoble 1, 38026, Grenoble Cedex, France
¹⁶ Helsinki Institute of Physics and Department of Physical Sciences, University of Helsinki, P.O. Box 64, 00014, Helsinki, Finland
¹⁷ Head Post Office, Joint Institute for Nuclear Research, Dubna, P.O. Box 79, 101000, Moscow, Russia
¹⁸ Institut für Experimentelle Kernphysik, Universität Karlsruhe, Postfach 6980, 76128, Karlsruhe, Germany
¹⁹ Institute of Nuclear Physics PAN, Ul. Radzikowskiego 152, 31142, Krakow, Poland
²⁰ Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy, 30055, Krakow, Poland
²¹ Lab. de l’Accélérateur Linéaire, IN2P3-CNRS, Université de Paris-Sud, , Bât. 200, 91405, Orsay Cedex, France
²² School of Physics and Chemistry, University of Lancaster, Lancaster, LA1 4YB, UK
²³ LIP, FCUL, IST, CFCUC, Av. Elias Garcia 14-1o, 1000, Lisboa Codex, Portugal
²⁴ Department of Physics, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK
²⁵ Dept. of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow, G12 8QQ, UK
²⁶ LPNHE, IN2P3-CNRS, Univ. Paris VI et VII, Tour 33 (RdC), 4 place Jussieu, 75252, Paris Cedex 05, France
²⁷ Department of Physics, University of Lund, Sölvegatan 14, 22363, Lund, Sweden
²⁸ IPNL, IN2P3-CNRS, Université Claude Bernard de Lyon, 69622, Villeurbanne Cedex, France
²⁹ Dipartimento di Fisica, Università di Milano and INFN-MILANO, Via Celoria 16, 20133, Milan, Italy
³⁰ Dipartimento di Fisica, Univ. di Milano-Bicocca and INFN-MILANO, Piazza della Scienza 3, 20126, Milan, Italy
³¹ IPNP of MFF, Charles Univ., Areal MFF, V Holesovickach 2, 18000, Praha 8, Czech Republic
³² NIKHEF, Postbus 41882, 1009 DB, Amsterdam, The Netherlands
³³ Physics Department, National Technical University, Zografou Campus, 15773, Athens, Greece
³⁴ Physics Department, University of Oslo, Oslo, 0316, Norway
³⁵ Dpto. Fisica, Univ. Oviedo, Avda. Calvo Sotelo s/n, 33007, Oviedo, Spain
³⁶ Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK
³⁷ Dipartimento di Fisica, Università di Padova and INFN, Via Marzolo 8, 35131, Padua, Italy
³⁸ Rutherford Appleton Laboratory, Chilton, Didcot, OX11 OQX, UK
³⁹ Dipartimento di Fisica, Università di Roma II and INFN, Tor Vergata, 00173, Rome, Italy
⁴⁰ Dipartimento di Fisica, Università di Roma III and INFN, Via della Vasca Navale 84, 00146, Rome, Italy
⁴¹ DAPNIA/Service de Physique des Particules, CEA-Saclay, 91191, Gif-sur-Yvette Cedex, France
⁴² Instituto de Fisica de Cantabria (CSIC-UC), Avda. los Castros s/n, 39006, Santander, Spain
⁴³ Inst. for High Energy Physics, Serpukov, P.O. Box 35, Protvino, Moscow Region, Russia
⁴⁴ J. Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
⁴⁵ Laboratory for Astroparticle Physics, University of Nova Gorica, Kostanjeviska 16a, 5000, Nova Gorica, Slovenia
⁴⁶ Department of Physics, University of Ljubljana, 1000, Ljubljana, Slovenia
⁴⁷ Fysikum, Stockholm University, Box 6730, 11385, Stockholm, Sweden
⁴⁸ Dipartimento di Fisica Sperimentale, Università di Torino and INFN, Via P. Giuria 1, 10125, Turin, Italy
⁴⁹ INFN, Sezione di Torino and Dipartimento di Fisica Teorica, Università di Torino, Via Giuria 1, 10125, Turin, Italy
⁵⁰ Dipartimento di Fisica, Università di Trieste and INFN, Via A. Valerio 2, 34127, Trieste, Italy
⁵¹ Istituto di Fisica, Università di Udine and INFN, 33100, Udine, Italy
⁵² C.P. 68528 Cidade Univ., Ilha do Fundão, Univ. Federal do Rio de Janeiro, 21945-970, Rio de Janeiro, Brazil
⁵³ Department of Radiation Sciences, University of Uppsala, P.O. Box 535, 75121, Uppsala, Sweden
⁵⁴ IFIC, Valencia-CSIC, and D.F.A.M.N., U. de Valencia, Avda. Dr. Moliner 50, 46100, Burjassot, Valencia, Spain
⁵⁵ Institut für Hochenergiephysik, Österr. Akad. d. Wissensch., Nikolsdorfergasse 18, 1050, Vienna, Austria
⁵⁶ Inst. Nuclear Studies and University of Warsaw, Ul. Hoza 69, 00681, Warsaw, Poland
⁵⁷ University of Warwick, Coventry, CV4 7AL, UK
⁵⁸ Fachbereich Physik, University of Wuppertal, Postfach 100127, 42097, Wuppertal, Germany

^* e-mail: Jan.Timmermans@cern.ch

Received: 26 July 2006
Revised: 28 January 2007
Published online: 29 March 2007

Abstract

A search for the pair production of fourth generation b’-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb^-1. No evidence for a signal was found. Upper limits on BR(b’→bZ) and BR(b’→cW) were obtained for b’ masses ranging from 96 to 103 GeV/c ². These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of , where V_cb′, V_tb′ and V_tb are elements of the extended CKM matrix.