  We report on a search for Lambda_b -> p pi- and Lambda_b -> p K- (and charge
conjugate) decays in p-pbar collisions at sqrt(s) = 1.96 TeV using 193 pb-1 of
data collected by CDFII experiment at the Fermilab Tevatron Collider. Data were
collected using a track trigger that has been optimized to select tracks
belonging to a secondary vertex that is typical of two body charmless decays of
b-flavored hadrons, including Lambda_b baryons. As no Lambda_b signal was
observed, we set the upper limits on the branching fractions BR(Lambda_b -> p
h-) where h is K or pi, of 2.3x10-5 at 90% C.L. and 2.9x10-5 at 95% C.L.
