On the effective lifetime of Bs → μμγ

We consider the B-s(0) -> mu(+)mu(-)gamma effective lifetime, and the related CP-phase sensitive quantity A(Delta Gamma s)(mu mu gamma), as a way to obtain qualitatively new insights on the current B-decay discrepancies. Through a fit comparing pre- to post-Moriond-2021 data we identify a few theory benchmark scenarios addressing these discrepancies, and featuring large CP violation in addition. We then explore the possibility of telling apart these scenarios with A(Delta Gamma s)(mu mu gamma), once resonance-modeling and form-factor uncertainties are taken into account. We do so in both regions of low and high invariant di-lepton mass-squared q(2). For low q(2), we show how to shape the integration range in order to reduce the impact of the phi-resonance modelling on the A(Delta Gamma s )(mu mu gamma)prediction. For high q(2), we find that the corresponding pollution from broad-charmonium resonances has a surprisingly small effect on A(Delta Gamma s)(mu mu gamma). This is due to a number of cancellations, that can be traced back to the complete dominance of semi-leptonic operator contributions for high q(2) - at variance with low q(2) - and to A(Delta Gamma s)(mu mu gamma) behaving like a ratio-of-amplitudes observable. Our study suggests that A(Delta Gamma s)(mu mu gamma) is - especially at high q(2) - a potentially valuable probe of short-distance CP-violating effects in the very same Wilson coefficients that are associated to current b -> s discrepancies. Its discriminating power, however, relies on progress in form-factor uncertainties. Interestingly, high q(2) is the region where B-s(0) ->mu(+)mu(-)gamma is already being accessed experimentally, and the region where form factors are more accessible through non-perturbative QCD methods.

Automated summary

By studying the B-s(0) -> mu(+)mu(-)gamma effective lifetime and the CP-phase sensitive quantity, we have identified new insights on current B-decay discrepancies and explored the potential of distinguishing different scenarios in high q(2) region. The high q(2) region could serve as a valuable probe for short-distance CP-violating effects, contingent on progress in addressing form-factor uncertainties.