First observation of the Cabibbo-suppressed decays Ξc%2b → Σ%2b π- π%2b and Ξc%2b → Σ- π%2b π%2b and measurement of their branching ratios

We report the first observation of two Cabibbo-suppressed decay modes, Ξc%2b → Σ%2b π- π%2b and Ξc%2b → Σ- π%2b π%2b. We observe 59 ± 14 over a background of 87, and 22 ± 8 over a background of 13 events, respectively, for the signals. The data were accumulated using the SELEX spectrometer during the 1996-1997 fixed target run at Fermilab, chiefly from a 600 GeV / cΣ- beam. The branching ratios of the decays relative to the Cabibbo-favored Ξc%2b → Ξ- π%2b π%2b are measured to be B (Ξc%2b → Σ%2b π- π%2b) / B (Ξc%2b → Ξ- π%2b π%2b) = 0.48 ± 0.20, and B (Ξc%2b → Σ- π%2b π%2b) / B (Ξc%2b → Ξ- π%2b π%2b) = 0.18 ± 0.09, respectively. We also report branching ratios for the same decay modes of the Λc%2b relative to Λc%2b → p K- π%2b. © 2008 Elsevier B.V.

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