1 New results on c-baryons and a search for cc-baryons in FOCUS Sergio P. Ratti a * a Istituto Nazionale di Fisica Nucleare, Sezione di Pavia Dipartimento di Fisica Nucleare e Teorica, Universita’ di Pavia via A. Bassi, 6 - I27100 Pavia (PV)- Italy 1. Cabibbo forbidden decays Λ + c → Σ + X FOCUS is a high statistic charm photoproduc- tion experiment. A total of about 7 billion trig- gers have been collected and many results have been published. The knowledge of the single Cabibbo suppressed decay rates of the Λ + c baryon are useful in testing theoretical predictions of the contributions to the inclusive decay amplitudes [1] as well as our theoretical understanding of the Ξ + c lifetime[2]. We measured the single Cabibbo suppressed decays Λ + c → Σ + (Kπ) o ; and the Cabibbo al- lowed decay Λ + c → Σ + K + K - , together with their branching ratios relative to the normaliz- ing mode Λ + c → Σ + π + π - , our highest statistic decay containing a Σ hyperon. The first decay may proceed via a 2-body chan- nel such as Σ + K * (892) o as well as via the 3-body channels Σ + K - π + or Σ - K + π - . The statistics is not sufficient to allow a Dalitz plot analysis; how- ever we see that the 2-body channel is dominant (see fig. 1a). The 2-body decay includes also a K - π + combination in the final state. The fit to * Coauthors are: J.Link, M.Reyes, P.M.Yager (UC DAVIS); J.Anjos, I.Bediaga, C.Gobel, J.Magnin, A. Massafferri, J.M. de Miranda, I.M.Pepe, A.C. dos Reis, (CPBF, Rio de Janeiro); S.Carrillo, E.Casimiro, A.S´ anchez-Hern´ andez, C.Uribe, F.Vasquez (CINVESTAV, M´ exico City); L.Cinquini, J.P.Cumalat, B.O’Reilly, J.E.Ramirez, E.W.Vaandering (CU Boulder); J.N.Butler, H.W.K.Cheung, I.Gaines, P.H.Garbincius, L.A.Garren, E.Gottschalk, P.H.Kasper, A.E.Kreymer, R.Kuschke (Fermilab); S.Bianco, F.L.Fabbri, S.Sarwar, A.Zallo (INFN Frascati); C.Cawlfield, D.Y.Kim, A.Rahimi, J.Wiss (UI Cham- paign); R.Gardner, A.Kryemadhi (IU Bloomington); Y.S.Chung, J.S.Kang, B.R.Ko, J.W.Kwak, K.B.Lee, H.Park (Korea Univer- sity, Seoul); G.Alimonti, M.Boschini, B.Caccianiga, P.D’Angelo, M.DiCorato, P.Dini, M.Giammarchi, P.Inzani, F.Leveraro, S.Malvezzi, D.Menasce, M.Mezzadri, L.Milazzo, L.Moroni, D.Pedrini, C.Pontoglio, F.Prelz, M.Rovere, S.Sala (INFN and Milano); T.F.Davenport III (UNC Asheville); L.Agostino, V.Arena, G.Boca, G.Bonomi, G.Gianini, G.Liguori, M.M.Merlo, D.Pantea, C.Riccardi, I.Segoni, P.Vitulo (INFN and Pavia); H.Hernandez, A.M.Lopez, H.Mendez, L.Mendez, E.Montiel, D.Olaya, A.Paris, J.Quinones, C.Rivera, W.Xiong, Y.Zhang (Mayaguez, Puerto Rico); J.R.Wilson (USC Columbia); K.Cho, T.Handler, R.Mitchell (UT Knoxville); D.Engh, M.Hosack, W.E.Johns, M.Nehring, P.D.Sheldon, K.Stenson, M.Webster (Vanderbilt); M.Sheaff (U. Wisconsin, Madison). the M [Σ + (Kπ) o ] distribution leads to a signal of (49 ± 10) Λ + c events. Fig.1b shows instead the absence of a signal in M (Σ - K + π + ), a configu- ration equivalent to Σ + K - π + . The fit returns a yield of (11 ± 10) events). This may justify the suppression of the 3-body channel since no extra pion is necessary to get the Σ + K * (892) o state. 0 5 10 15 20 25 30 35 2.2 2.25 2.3 2.35 2.4 0 5 10 15 20 25 30 2.15 2.2 2.25 2.3 2.35 2.4 2.45 c) 0 50 100 150 200 250 300 2.2 2.25 2.3 2.35 2.4 Figure 1. Mass distributions: a- M(Σ + K * (892) o ) (with K * (892) o → K + π - ); b- distributions of M(Σ - K + π + ); c- reference signal M(Σ + π + π - ). The distributions are fit with a double Gaussian for the signal plus a linear background. The normalizing mode (shown in fig. 1c) leads to a signal of (1706 ± 88) Λ + c events. We get a first measurement of the relative branching ratio Γ(Σ + K * [892]) Γ(Σ + π + π - ) =0.078 ± .018 ± .013 and a first estimate of an upper limit for the rel- ative branching ratio Γ(Σ - K + π + ) Γ(Σ + K * [892]) < 0.35 (90% confidence level). 2. The Λ + c → Σ + K + K - decay. We also studied the events Λ + c → Σ + K + K - as well as the 2-body configurations which may be present. The branching ratios are again related to the normalization channel Λ + c → Σ + π + π - since the dominant source of systematics is the selec- tion and isolation of the Σ hyperon.