Semileptonic decay of heavy baryons in a constituent quark model.

摘要

The semileptonic decays of heavy baryons, Λ Q and ΛQ are treated in the framework of a constituent quark model. Both nonrelativistic and semirelativistic Hamiltonians are used to obtain the baryon wave functions from a fit to the spectra, and the wave functions are expanded in both the harmonic oscillator and Sturmian bases. The latter basis leads to form factors in which the kinematic dependence on the square of the momentum transfer (q 2) is in the form of multipoles, and the resulting form factors fall faster as a function of q2 in the available kinematic ranges. As a result, decay rates obtained in the two models using the Sturmian basis are significantly smaller than those obtained using the harmonic oscillator basis. In the case of the Λc, decay rates calculated using the Sturmian basis are closer to the experimentally reported rates. However, we find a semileptonic branching fraction for the Λ c to decay to excited Λ* states of 11% to 19%, in contradiction with what is assumed in available experimental analyses. Our prediction for the Λb semileptonic decays is that decays to the ground state Λc provide a little less than 70% of the total semileptonic decay rate. For the decays Λ b → Λc the analytic form factors we obtain satisfy the relations expected from heavy-quark effective theory at the non-recoil point, at leading and next-to-leading orders in the heavy-quark expansion. In addition, some features of the heavy-quark limit are shown to naturally persist as the mass of the heavy quark in the daughter baryon is decreased.; For the case of OQ decays there are no experimentally determined rates. However, we find that our analytical and numerical results for the form factors and rates of OQ decays compare well with HQET predictions. Our results indicate a significant inelastic branching fraction for Ob → O c(*) decays, which is about 35% in all of our models. For Oc → xi (*) decays the elastic fraction dominates (about 84%) but it does not saturate the decay.