Time-reversal asymmetries in $\Lambda_b$ semileptonic decays

TL;DR

This paper investigates time-reversal asymmetries in $ ext{Lambda}_b$ semileptonic decays, proposing their use as probes for new physics beyond the Standard Model, especially right-handed currents, with potential observation at LHCb.

Contribution

It provides a detailed analysis of angular distributions and time-reversal asymmetries in $ ext{Lambda}_b$ decays, highlighting their sensitivity to new physics effects.

Findings

Time-reversal asymmetries vanish in the Standard Model.

Asymmetries are sensitive to right-handed currents from new physics.

Potential for experimental observation at LHCb.

Abstract

We study the decays of $\Lambda_b \to \Lambda_c(\to B_n f) \ell ^- \overline{\nu}$ with $\ell = e, \mu, \tau$, where $B_n$ and $f$ are the daughter baryons and the rest of the particles in $\Lambda_c$ cascade decays, respectively. In particular, we examine the full angular distributions with polarized $\Lambda_b$ and lepton mass effects, in which the time-reversal asymmetries are identified. We concentrate on the decay modes of $\Lambda_b \to \Lambda_c(\to p K^- \pi^+) \ell ^- \overline{\nu}$ 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.