Time-reversal asymmetries in Λ_(b)→Λ(→pπ^(−))ℓ^(+)ℓ^(−)

We study the decays ofΛb→Λ(→pπ^(−))ℓ^(+)ℓ^(−)withℓ=(e,μ,τ).We examine the full angular distributions with polarizedΛb,where the T-odd observables are identified.We discuss the possible effects of new physics(NP)and find that the T-odd observables are sensitive to them as they vanish in the standard model.Special attention is given to the interference of(pseudo)scalar operators with(axial)vector operators in polarized Λ_(b)→Λ(→pπ^(−))τ^(+)τ^(−),which are studied for the first time.Their effects are proportional to the lepton masses and therefore may evade the constraint from Λ_(b)→Λ(→pπ^(−))μ^(+)μ^(−) at the LHCb naturally.AsΛ_(b)→Λ(→pπ^(−))τ^(+)τ^(−) is uncontaminated by the charmonia resonance,it provides a clean background to probe NP.In addition,we show that the experimental central value of K10 in Λ_(b)→Λ(→pπ^(−))μ^(+)μ^(−) at the LHCb can be explained by the NP case,which couples to the right-handed quarks and leptons.The polarization fraction of Λ_(b) at the LHCb is found to be consistent with zero regardless of the NP scenarios.