First Observation of the Cabibbo-suppressed Decays Xic+ -> Sigma+ pi- pi+ and Xic+ -> Sigma- pi+ pi+ and Measurement of their Branching Ratios
Abstract
We report the first observation of two Cabibbo-suppressed decay modes, Xic+ -> Sigma+ pi- pi+ and Xic+ -> Sigma- pi+ pi+. 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 600GeV/c Sigma- beam. The branching ratios of the decays relative to the Cabibbo--favored Xic+ -> Xi- pi+ pi+ are measured to be B(Xic+ -> Sigma+ pi- pi+)/B(Xic+ -> Xi- pi+ pi+) = 0.48+/-0.20, and B(Xic+ -> Sigma- pi+ pi+)/B(Xic+ -> Xi- pi+ pi+) = 0.18+/-0.09, respectively. We also report branching ratios for the same decay modes of the Lambdac+ relative to Lambdac+ -> p K- pi+.
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