First observation of the beauty baryon Λb in the decay channel Λb→J/ψΛ at the CERN proton-antiproton collider

C. Albajar, M. G. Albrow, O. C. Allkofer, K. Ankoviak, R. Apsimon, B. Aubert, C. Bacci, S. Bartha, G. Bauer, A. Bettini, A. Bezaguet, P. Biddulph, H. Bohn, A. Böhrer, R. Bonino, K. Bos, M. Botlo, D. Brockhausen, C. Buchanan, A. BushbeckG. Busetto, A. Caner, P. Casoli, H. Castilla-Valdez, F. Cavanna, P. Cennini, S. Centro, F. Ceradini, G. Ciapetti, S. Cittolin, E. Clayton, D. Cline, J. Colas, R. Conte, J. A. Coughlan, D. Dau, C. Daum, M. Della Negra, C. Demoulin, D. Denegri, H. Dibon, A. DiCiaccio, F. J. Diez Hedo, L. Dobrzynski, J. Dorenbosch, J. D. Dowell, D. Drijard, K. Eggert, E. Eisenhandler, N. Ellis

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84 Scopus citations


We report on the first observation of the beauty baryon Λb in an exclusive decay channel at the CERN pp collider. Using 4.7 pb-1 of muon data collected in the 1988/89 collider runs we reconstruct 16±5 Λb's in the decay mode Λb→ J ψΛ above a background of 9±1 events, corresponding to a significance of about five standard deviations. We measure the Λb mass to be mΛb=5640±50±30 MeV/c2. Using the beauty cross-section measured by UA1 we deduce for the product of the production fraction and branching ratio fΛb Br (Λb→ J ψΛ)=(1.8±1.0)×10-10. Our sample contains three-muon event in which the beauty particle opposite to the Λb is tagged by the third muon. We also observe an indication of a signal in the decay channel B0→ J ψK0* with a significance of three standard deviations.

Original languageEnglish (US)
Pages (from-to)540-548
Number of pages9
JournalPhysics Letters B
Issue number4
StatePublished - Dec 26 1991

Bibliographical note

Funding Information:
We are thankful to the management and staff of CERN and of all participating institutes for their vigorous support of the experiment. The following funding agencies have contributed to this programme: Fonds zur F6rderung der Wissenschaftlichen For-schung, Austria; Valtion luonnontieteellinen toimikunta, Suomen Akatemia, Finland; Institut National de Physique Nucl6aire et de Physique des Particules and Institut de Recherche Fon-damentale (CEA), France; Bundesministerium fiir Forschung und Technologic, FRG; Istituto Nazionale di Fisica Nucleare, Italy; Science and Engineering Research Council, UK; Stichting Voor Fundamenteel Onderzoek der Ma-terie, The Netherlands; Centro de Investigaciones Energetica, Medioam-bientales y Tecnologicas (CIEMAT), Spain; Department of Energy, USA. Thanks are also due to the following people who have worked with the collaboration in the preparations for and data collection on the runs described here: L. Baumard, F. Bernasconi, D. Brozzi, V. Cec-coni, L. Dumps, G. Fetchenhauer, G. Gallay, S. La-zic, J.C. Michelon, S. Pavlon and L. Pollet.


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