Second-order power corrections in the heavy-quark effective theory. II. Baryon form factors

The analysis of 1/${\mathit{m}}_{\mathit{Q}}^2$ corrections of the previous paper is extended to the semileptonic decays of heavy baryons. We focus on the simplest case, the ground-state ${\mathrm{\Lambda }}_{\mathit{Q}}$ baryons, in which the light degrees of freedom are in a state of zero total angular momentum. The formalism, while identical in spirit, is considerably less cumbersome than for heavy mesons. The general results are applied to the semileptonic decay ${\mathrm{\Lambda }}_{\mathit{b}}$→${\mathrm{\Lambda }}_{\mathit{c}}$lν. An estimate of the leading power corrections to the decay rate at zero recoil, which are of order 1/${\mathit{m}}_{\mathit{Q}}^2$, is presented. It is pointed out that a measurement of certain asymmetry parameters would provide a direct measurement of 1/${\mathit{m}}_{\mathit{Q}}^2$ corrections. Finally, it is shown how the analysis could be extended to include excited heavy baryons such as the ${\mathrm{\Sigma }}_{\mathit{Q}}$ and the ${\mathrm{\Sigma }}_{\mathit{Q}}^{\mathrm{*}}$.