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

1991; Elsevier BV; Volume: 273; Issue: 4 Linguagem: Inglês

10.1016/0370-2693(91)90311-d

1873-2445

C. Albajar, M. Albrow, O. C. Allkofer, K. Ankoviak, R. Apsimon, B. Aubert, C. Bacci, S. Bartha, G. Bauer, A. Bettini, A. Bézaguet, P. Biddulph, H. Böhn, A. Böhrer, R. Bonino, K. Bos, M. Botlo, D. Brockhausen, C. Buchanan, A. Bushbeck, G. 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. Colás, 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. Dobrzyński, J. Dorenbosch, J.D. Dowell, D. Drijard, K. Eggert, E. Eisenhandler, N. Ellis, H. Evans, H. Faissner, M. Felcini, I.F. Fensome, J. Ferrando, L. Fortson, T. A. Fuess, J. Garvey, A. Geiser, A. Givernaud, A. Gonidec, B. Álvarez González, Jonathan M. Gregory, J. Gronberg, D. Holthuizen, W. Jank, G. Jorat, M. I. Josa, P.I.P. Kalmus, V. Karimäki, I. R. Kenyon, R. Kinnunen, M. Krammer, D. Kryn, F. Lacava, S. Lammel, M. P. J. Landon, Y. Lemoigne, S. Levegrün, D. Linglin, P. Lipa, C. Markou, M. Markytan, M.A. Marquina, R. Martinelli, G. Maurin, S. J. McMahon, J.-P. Mendiburu, A. T. Meneguzzo, J.-P. Merlo, T. Meyer, T. Moers, M. Mohammadi, K. Morgan, A. Morsch, André Moulin, Th. Müller, Raúl C. Mun̄oz, L. Naumann, P. Nédélec, M. Nikitas, A. Nisati, A. Norton, V. O’Dell, S. Otwinowski, G. Pancheri, M. Passaseo, F. Pauss, E. Petrolo, G. Piano Mortari, E. Pietarinen, M. Pimiä, A. Placci, L. Pontecorvo, J.-P. Porte, Richard L. Priem, R. Prosi, E. Radermacher, M. Rauschkolb, H. Reithler, J.-P. Revol, D. Robinson, T. Rodrigo, J. Rohlf, C. Rubbia, G. Sajot, J.M. Salicio, D. Samyn, D. Schinzel, D. Schleichert, M. Schröder, C. Seez, T.P. Shah, P. Sphicas, D. H. Stork, C. Stubenrauch, K. Sumorok, F. Szoncsó, C.H. Tan, A. Taurok, L. Taylor, S. Tether, H. Teykal, G. Thompson, E. Torrente-Luján, H. Tuchscherer, J. Tuominiemi, W. van de Guchte, A. van Dijk, M. Vargas, S. Veneziano, J.P. Vialle, T. Virdee, W. von Schlippe, J. Vrána, V. Vuillemin, K. Wacker, Hermann Wagner, X. Wu, C.-E. Wulz, M. Yvert, I. Zacharov, L. Zanello, Y. Zolnierowski, P. Zotto,

High-Energy Particle Collisions Research

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→JψΛ 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→JψΛ)=(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→JψK0∗ with a significance of three standard deviations.