Time-reversal asymmetries in ${\mathrm{\Lambda }}_b$ semileptonic decays

We study the decays of ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c(\to B_{n}f){\mathrm{\ell }}^{-}\bar{\nu }$ with $\mathrm{\ell }=e,\mu ,\tau$, where $B_n$ and $f$ are the daughter baryons and the rest of the particles in ${\mathrm{\Lambda }}_c$ cascade decays, respectively. In particular, we examine the full angular distributions with polarized ${\mathrm{\Lambda }}_b$ and lepton mass effects, in which the time-reversal asymmetries are identified. We concentrate on the decay modes of ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c(\to p{K}^{-}{\pi }^{+}){\mathrm{\ell }}^{-}\bar{\nu }$ to demonstrate their experimental feasibility. We show that the observables associated with the time-reversal asymmetries are useful to search for new physics as they vanish in the standard model. Explicitly, we find that they are sensitive to the right-handed current from new physics, and possible to be observed at LHCb.