Infinite momentum frame calculation of semileptonic heavy Λb→Λc transitions including HQET improvements

We calculate the transition form factors that occur in heavy Λ-type baryon semileptonic decays such as, e.g., in Λb→Λc++l-+bar νl. We use Bauer-Stech-Wirbel-type infinite momentum frame wave functions for the heavy Λ-type baryons which we assume to consist of a heavy quark and a light spin-isospin zero diquark system. The form factors at q2=0 are calculated from the overlap integrals of the initial and final Λ-type baryon states. To leading order in the heavy mass scale the structure of the form factors agrees with the HQET predictions including the normalization at zero recoil. The leading order ω dependence of the form factors is extracted by scaling arguments. By comparing the model form factors with the HQET predictions at O(1/mQ) we obtain a consistent set of model form factors up to O(1/mQ). With our preferred choice of parameter values we find that the contribution of the nonleading form factor is practically negligible. We use our form factor predictions to compute rates, spectra, and various asymmetry parameters for the semileptonic decay Λb→Λc++l-+bar νl. copyright 1997 The American Physical Society