PHYSICAL REVIEW LETTERS, vol.84, no.9, pp.1857-1861, 2000 (SCI-Expanded)
We report the first observation of the Cabibbo-suppressed charm baryon decay Xi(c)(+) --> pK(-)pi(+) We observe 150 +/- 22 +/- 5 events for the signal. The data were accumulated using the SELEX spectrometer during the 1996-1997 fixed target run at Fermilab, chiefly from a 600 GeV/c Sigma(-) beam. The branching fractions of the decay relative to the Cabibbo-favored Xi(c)(+) --> Sigma(+)K(-)pi(+) and Xi(c)(+) --> Xi(-)pi(+)pi(+) are measured to be B(Xi(c)(+) --> pK(-)pi(+))/B(Xi(c)(+) --> Sigma(+)K(-)pi(+)) = 0.22 +/- 0.06 +/- 0.03 and B(Xi(c)(+) --> pK(-)pi(+))/B(Xi(c)(+) --> Xi(-)pi(+)pi(+)) = 0.20 +/- 0.04 +/- 0.02, respectively.