Bayesian analysis of $b\to s\mu^+\mu^-$ Wilson coefficients using the full angular distribution of $\Lambda_b\to \Lambda(\to p\, \pi^-)\mu^+\mu^-$ decays

TL;DR

This paper uses updated angular distribution measurements of Lambda_b decays to constrain Wilson coefficients in the effective Hamiltonian, finding compatibility with the Standard Model and B-meson decay anomalies, and analyzing the impact of various observables.

Contribution

It provides the first comprehensive Bayesian analysis of Lambda_b decay data to constrain $b\to s\mu^+\mu^-$ Wilson coefficients, incorporating recent experimental updates.

Findings

Good compatibility with the Standard Model.

Constraints on Wilson coefficients consistent with B-meson anomalies.

Insights into Lambda_b production polarization at LHCb.

Abstract

Following updated and extended measurements of the full angular distribution of the decay $\Lambda_b\to \Lambda(\to p\,\pi^-)\mu^+\mu^-$ by the LHCb collaborations, as well as a new measurement of the $\Lambda \to p \pi^-$ decay asymmetry parameter by the BESIII collaboration, we study the impact of these results on searches for non-standard effects in exclusive $b\to s\mu^+\mu^-$ decays. To this end, we constrain the Wilson coefficients $\mathcal{C}_{9}$ and $\mathcal{C}_{10}$ of the numerically leading dimension-six operators in the weak effective Hamiltonian, in addition to the relevant nuisance parameters. In stark contrast to previous analyses of this decay mode, the changes in the updated experimental results lead us to find very good compatibility with both the Standard Model and with the $b\to s\mu^+\mu^-$ anomalies observed in rare $B$-meson decays. We provide a detailed analysis of the impact of the partial angular distribution, the full angular distribution, and the $\Lambda_b\to \Lambda\mu^+\mu^-$ branching fraction on the Wilson coefficients. In this process, we are also able to constrain the size of the production polarization of the $\Lambda_b$ baryon at LHCb.