The tree-level semileptonic ${\Lambda }_b\to pl\nu$ and ${\Lambda }_c\to nl\nu$ transitions are investigated using the light cone QCD sum rules approach in full theory. The spin $1/2$, ${\Lambda }_Q$ baryon with $Q=b$ or $c$, is considered by the most general form of its interpolating current. The time ordering product of the initial and transition currents is expanded in terms of the nucleon distribution amplitudes with different twists. Considering two sets of independent input parameters entering to the nucleon wave functions, namely, QCD sum rules and lattice QCD parameters, the related form factors and their heavy quark effective theory limits are calculated and compared with the existing predictions of other approaches. It is shown that our results satisfy the heavy quark symmetry relations for lattice input parameters and $b$ case exactly and the maximum violation is for charm case and QCD sum rules input parameters. The obtained form factors are used to compute the transition rates both in full theory and heavy quark effective theory. A comparison of the results on decay rate of ${\Lambda }_b\to pl\nu$ with those predicted by other phenomenological methods or the same method in heavy quark effective theory with different interpolating current and distribution amplitudes of the ${\Lambda }_b$ is also presented.

• Received 12 August 2009

DOI:https://doi.org/10.1103/PhysRevD.80.096007