Faking $B_s \to \mu^+\mu^-$

TL;DR

This paper investigates how certain rare decay processes involving B_s mesons and soft particles can mimic the B_s to mu+ mu- decay, showing these effects are negligible within the Standard Model.

Contribution

It provides a model-independent calculation of B_s decay modes with photons or neutrinos, demonstrating their minimal impact on the observed B_s to mu+ mu- decay rate.

Findings

Contributions from B_s to mu+ mu- X decays are below 1% of the total.

Standard Model effects are consistent with experimental measurements.

Potential New Physics effects are not significantly masked by these processes.

Abstract

Recent evidence from observation of the flavor-changing neutral current decay B_s to mu+ mu- by the LHCb collaboration B(B_s to mu^+ mu^-) = (3.2 * 10^{-9}), is consistent with the latest standard model prediction B(B_s to mu^+ mu^-) = (3.23 +- 0.27) * 10^{-9}. While New Physics can still affect this decay amplitude, its contribution is certainly not the dominant one. We analyze branching ratios of the decays B_s to mu+ mu- X, with X = a photon or neutrino anti-neutrino pair, which can mimic B_s to mu+ mu- on portions of the parameter space where X is soft. We perform a model-independent standard model calculation of those processes incorporating heavy quark and chiral symmetries of QCD. We show that the considered contributions contribute to B_s to mu+ mu- at a sub-percent level.