Recently there has been much interest in the tauonic semileptonic meson decays $B\to D+\tau +{\nu }_{\tau }$ and $B\to D^{*}+\tau +{\nu }_{\tau }$, where one has found larger rates than what is predicted by the Standard Model. We analyze the corresponding semileptonic baryon decays ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}+{\tau }^{-}+{\overline{\nu }}_{\tau }$ with particular emphasis on the lepton helicity flip and scalar contributions which vanish for zero lepton masses. We calculate the total rate, the differential decay distributions, the longitudinal and transverse polarization of the daughter baryon ${\mathrm{\Lambda }}_c^{+}$ and the $\tau$ lepton, and the lepton-side forward-backward asymmetries. The nonvanishing polarization of the daughter baryon ${\mathrm{\Lambda }}_c^{+}$ leads to hadron-side asymmetries in e.g. the decay ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Lambda }}^0+{\pi }^{+}$ and azimuthal correlations between the two final-state decay planes which we specify. We provide numerical results on these observables using results of the covariant confined quark model. We find large lepton mass effects in the $q^2$ spectra and in the polarization observables.

• Received 18 February 2015

DOI:https://doi.org/10.1103/PhysRevD.91.074001