1st Observation of the Beauty Baryon-lambda-b In the Decay Channel Lambda-b-]j/psi-lambda At the Cern Proton-antiproton Collider

Albajar, C.; Albrow, M. G.; Allkofer, O. C.; Ankoviak, K.; Apsimon, R.; Aubert, B.; Bacci, C.; Bartha, S.; Bauer, G.; Bettini, Alessandro; Bezaguet, A.; Biddulph, P.; Bohn, H.; Bohrer, A.; Bonino, R.; Bos, K.; Botlo, M.; Brockhausen, D.; Buchanan, C.; Buschbeck, B.; Busetto, Giovanni; Caner, A.; Casoli, P.; Castillavaldez, H.; Cavanna, F.; Cennini, P.; Centro, Sandro; Ceradini, F.; Ciapetti, G.; Cittolin, S.; Clayton, E.; Cline, D.; Colas, J.; Conte, R.; Coughlan, J. A.; Dau, D.; Daum, C.; Dellanegra, M.; Demoulin, M.; Denegri, D.; Dibon, H.; Diciaccio, A.; F. J. D.,; Dobrzynski, L.; Dorenbosch, J.; Dowell, J. D.; Drijard, D.; Eggert, K.; Eisenhandler, E.; Ellis, N.; Evans, H.; Faissner, H.; Felcini, M.; Fensome, I. F.; Ferrando, A.; Fortson, L.; Fuess, T.; Garvey, J.; Geiser, A.; Givernaud, A.; Gonidec, A.; Gonzalez, B.; Gregory, J. M.; Gronberg, J.; Holthuizen, D. J.; Jank, W.; Jorat, G.; Josa, M. I.; P. I. P.,; Karimaki, V.; Kenyon, I.; Kinnunen, R.; Krammer, M.; Kryn, D.; Lacava, F.; Lammel, S.; Landon, M.; Lemoigne, Y.; Levegrun, S.; Linglin, D.; Lipa, P.; Markou, C.; Markytan, M.; Marquina, M. A.; Martinelli, R.; Maurin, G.; Mcmahon, S.; Mendiburu, J. P.; Meneguzzo, ANNA TERESA; Merlo, J. P.; Meyer, T.; Moers, T.; Mohammadi, M.; Morgan, K.; Morsch, A.; Moulin, A.; Muller, T.; Munoz, R.; Naumann, L.; Nedelec, P.; Nikitas, M.; Nisati, A.; Norton, A.; Odell, V.; Otwinowski, S.; Pancheri, G.; Passaseo, M.; Pauss, F.; Petrolo, E.; Mortari, G. P.; Pietarinen, E.; Pimia, M.; Placci, A.; Pontecorvo, L.; Porte, J. P.; Priem, R.; Prosi, R.; Radermacher, E.; Rauschkolb, M.; Reithler, H.; Revol, J. P.; Robinson, D.; Rodrigo, T.; Rohlf, J.; Rubbia, C.; Saiot, G.; Salicio, J. M.; Samyn, D.; Schinzel, D.; Schleichert, R.; Schroder, M.; Seez, C.; Shah, T. P.; Sphicas, P.; Stork, D.; Stubenrauch, C.; Sumorok, K.; Szoncso, F.; Tan, C. H.; Taurok, A.; Taylor, I.; Tether, S.; Teykal, H.; Thompson, G.; Torrentelujan, E.; Tuchscherer, H.; Tuominiemi, J.; Vandeguchte, W.; Vandijk, A.; Vargas, M.; Veneziano, S.; Vialle, J. P.; Virdee, T. S.; Vonschlippe, W.; Vrana, J.; Vuillemin, V.; Wacker, K.; Wagner, H.; Wu, X.; Wulz, C. E.; Yvert, M.; Zacharov, I.; Zanello, L.; Zolnierowski, Y.; Zotto, Pierluigi

doi:10.1016/0370-2693(91)90311-D

We report on the first observation of the beauty baryon LAMBDA(b) in an exclusive decay channel at the CERN ppBAR collider. Using 4.7 pb-1 of muon data collected in the 1988/89 collider runs we reconstruct 16 +/- 5 LAMBDA(b)'s in the decay mode LAMBA(b) --> J/psi-LAMBDA above a background of 9 +/- 1 events, corresponding to a significance of about five standard deviations. We measure the LAMBDA(b) mass to be m(LAMBDA(b)) = 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 f(LAMBDA(b)) Br(LAMBDA(b) --> J/psi-LAMBDA) = (1.8 +/- 1.0) X 10(-3). Our sample contains a three-muon event in which the beauty particle opposite to the LAMBDA(b)BAR is tagged by the third muon. We also observe an indication of a signal in the decay channel B0 --> J/psi-K0* with a significance of three standard deviations.