Bayesian analysis of b →sμ+μ- Wilson coefficients using the full angular distribution of Λb → Λ (→pπ-)μ+μ- decays

Following updated and extended measurements of the full angular distribution of the decay Λb→Λ(→pπ-)μ+μ- by the LHCb collaborations, as well as a new measurement of the Λ→pπ- decay asymmetry parameter by the BESIII collaboration, we study the impact of these results on searches for nonstandard effects in exclusive b→sμ+μ- decays. To this end, we constrain the Wilson coefficients C9 and C10 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→sμ+μ- 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 Λb→Λμ+μ- branching fraction on the Wilson coefficients. In this process, we are also able to constrain the size of the production polarization of the Λb baryon at LHCb.