Using $Λ_b\to Λμ^+μ^-$ data within a Bayesian analysis of $|ΔB| = |ΔS| = 1$ decays

Abstract

We study the impact of including the baryonic decay $Λ_b\to Λ(\to p π^-)μ^+μ^-$ in a Bayesian analysis of $|ΔB | = |ΔS| = 1$ transitions. We perform fits of the Wilson coefficients $C_{9}$, $C_{9'}$, $C_{10}$ and $C_{10'}$, in addition to the relevant nuisance parameters. Our analysis combines data for the differential branching fraction and three angular observables of $Λ_b\to Λ(\to p π^-)μ^+μ^-$ with data for the branching ratios of $B_s \to μ^+μ^-$ and inclusive $b \to s\ell^+\ell^-$ decays. Newly available precise lattice QCD results for the full set of $Λ_b \to Λ$ form factors are used to evaluate the observables of the baryonic decay. Our fits prefer shifts to $C_{9}$ that are opposite in sign compared to those found in global fits of only mesonic decays, and the posterior odds show no evidence of physics beyond the Standard Model. We investigate a possible hadronic origin of the observed tensions between theory and experiment.

9 pages, 2 figures; v2 as published: added some clarifications, changed setup for model comparisons, expanded conclusions