Time-reversal asymmetries in $Λ_b$ semileptonic decays

Abstract

We study the decays of $Λ_b \to Λ_c(\to B_n f) \ell ^- \overlineν$ with $\ell = e, μ, τ$, where $B_n$ and $f$ are the daughter baryons and the rest of the particles in $Λ_c$ cascade decays, respectively. In particular, we examine the full angular distributions with polarized $Λ_b$ and lepton mass effects, in which the time-reversal asymmetries are identified. We concentrate on the decay modes of $Λ_b \to Λ_c(\to p K^- π^+) \ell ^- \overlineν$ 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.