CP violation in leptonic rare Bs0 decays as a probe of new physics

Abstract

The decay Bs0→μ+μ- is a key probe for the search of physics beyond the Standard Model. While the current measurements of the corresponding branching ratio agree with the Standard Model within the uncertainties, significant New-Physics effects may still be hiding in Bs0→μ+μ-. In order to reveal them, the observable AΔΓsμμ, which is provided by the decay width difference Δ Γ s of the Bs0-meson system, plays a central role. We point out that a measurement of a CP-violating observable Sμμ, which is induced through interference between Bs0–B¯s0 mixing and Bs→ μ+μ- decay processes, is essential to obtain the full picture, in particular to establish new scalar contributions and CP-violating phases. We illustrate these findings with future scenarios for the upgrade(s) of the LHC, exploiting also relations which emerge within an effective field theory description of the Standard Model, complemented with New Physics entering significantly beyond the electroweak scale.