Hint of Lepton Flavour Non-Universality in $B$ Meson Decays

TL;DR

This paper investigates potential new physics explanations for the observed deviation in the R_K ratio in B meson decays, suggesting a preference for new physics affecting muons over electrons based on Bayesian analysis.

Contribution

It provides a model-independent Bayesian analysis of new physics effects in B decays, relaxing lepton universality and comparing hypotheses with experimental data.

Findings

Data slightly favors new physics in the muon sector

Bayesian fit constrains new physics Wilson coefficients

Comparison of hypotheses using Bayes Factors

Abstract

The LHCb collaboration has recently presented their result on R_K = BR(B+ -> K+ mu+ mu-)/ BR(B+ -> K+ e+ e-) for the dilepton invariant mass bin m_{ll}^2 = 1-6 GeV^2 (l = mu, e). The measurement shows an intriguing 2.6 sigma deviation from the Standard Model (SM) prediction. In view of this, we study model independent New Physics (NP) explanations of R_K consistent with other measurements involving b -> s l l transition, relaxing the assumption of lepton universality. We perform a Bayesian statistical fit to the NP Wilson Coefficients and compare the Bayes Factors of the different hypotheses in order to quantify their goodness-of-fit. We show that the data slightly favours NP in the muon sector over NP in the electron sector.