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

• Published in: Physics letters. B 1991-12, Vol.273 (4), p.540-548
• Main Authors: Albajar, C., Albrow, M.G., Allkofer, O.C., Ankoviak, K., Aubert, B., Bacci, C., Bauer, G., Bettini, A., Bohn, H., Böhrer, A., Bonino, R., Botlo, M., Brockhausen, D., Busetto, G., Caner, A., Casoli, P., Castilla-Valdez, H., Ceradini, F., Ciapetti, G., Cittolin, S., Clayton, E., Cline, D., Colas, J., Conte, R., Coughlan, J.A., Daum, C., Della Negra, M., Denegri, D., Dibon, H., Diez Hedo, F.J., Dorenbosch, J., Dowell, J.D., Drijard, D., Eggert, K., Eisenhandler, E., Ellis, N., Evans, H., Faissner, H., Felcini, M., Fensome, I.F., Fortson, L., Fuess, T., Garvey, J., Gonidec, A., Gonzalez, B., Holthuizen, D.J., Kalmus, P.I.P., Kinnunen, R., Krammer, M., Kryn, D., Lammel, S., Landon, M., Levegrün, S., Linglin, D., Markou, C., Marquina, M.A., Martinelli, R., Maurin, G., McMahon, S., Moers, T., Morgan, K., Morsch, A., Moulin, A., Muller, Th, Munoz, R., Naumann, L., Nedelec, P., Nikitas, M., Nisati, A., Otwinowski, S., Passaseo, M., Petrolo, E., Pietarinen, E., Pimiä, M., Pontecorvo, L., Rauschkolb, M., Robinson, D., Sajot, G., Salicio, J.M., Schinzel, D., Schleichert, D., Seez, C., Shah, T.P., Sphicas, P., Szoncso, F., Tan, C.H., Teykal, H., Torrente-Lujan, E., van de Guchte, W., van Dijk, A., Veneziano, S., Vialle, J.P., Virdee, T.S., von Schlippe, W., Vrana, J., Wagner, H., Wulz, C.-E., Yvert, M., Zacharov, I., Zotto, P.
• Format: Article
• Language: English
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/0370-2693(91)90311-D

We report on the first observation of the beauty baryon Λ b in an exclusive decay channel at the CERN p p collider. Using 4.7 pb −1 of muon data collected in the 1988/89 collider runs we reconstruct 16±5 Λ b 's in the decay mode Λ b → J ψΛ above a background of 9±1 events, corresponding to a significance of about five standard deviations. We measure the Λ b mass to be m Λb =5640±50±30 MeV/ c 2. Using the beauty cross-section measured by UA1 we deduce for the product of the production fraction and branching ratio f Λ b Br (Λ b → J ψΛ )=(1.8±1.0)×10 -10 . Our sample contains three-muon event in which the beauty particle opposite to the Λ b is tagged by the third muon. We also observe an indication of a signal in the decay channel B 0→ J ψ K 0∗ with a significance of three standard deviations.