Using $\Lambda_b\to \Lambda\mu^+\mu^-$ data within a Bayesian analysis of $|\Delta B| = |\Delta S| = 1$ decays

TL;DR

This paper incorporates baryonic decay data into a Bayesian analysis of $| riangle B|=| riangle S|=1$ transitions, refining Wilson coefficient estimates and assessing potential new physics signals.

Contribution

It introduces the first Bayesian fit including $ ext{Lambda}_b$ decay data with updated lattice QCD form factors, providing new insights into Wilson coefficients and Standard Model consistency.

Findings

Fits favor opposite sign shifts in $C_9$ compared to mesonic-only analyses

No evidence found for physics beyond the Standard Model

Inclusion of baryonic data refines constraints on decay parameters

Abstract

We study the impact of including the baryonic decay $\Lambda_b\to \Lambda(\to p \pi^-)\mu^+\mu^-$ in a Bayesian analysis of $|\Delta B | = |\Delta S| = 1$ 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 $\Lambda_b\to \Lambda(\to p \pi^-)\mu^+\mu^-$ with data for the branching ratios of $B_s \to \mu^+\mu^-$ and inclusive $b \to s\ell^+\ell^-$ decays. Newly available precise lattice QCD results for the full set of $\Lambda_b \to \Lambda$ 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.