On the impact of meson mixing on Bs→ ϕee angular observables at low q2

A bstract Decays based on the b → sγ transition are expected to yield left-handed photons in the Standard Model, but could be particularly sensitive to New Physics contributions modifying the short-distance Wilson coefficients C 7 and C 7′ defined in the low-energy Effective Field Theory. These coefficients can be determined by combining observables of several modes, among which B s → ϕee at low q 2 , in a kinematic range where the photon-pole is dominant. We investigate the impact of B s − B ¯ s mixing on the angular observables available for this mode, which induces a time-dependent modulation governed by interference terms between mixing and decay that are sensitive to the moduli and phases of C 7 and C 7′ . These interference terms can be extracted through a time-dependent analysis but they also affect time-integrated observables. In particular, we show that the asymmetries A T 2 and A T Im ; CP receive terms of potentially similar size from mixing-independent and mixing-induced terms, and we discuss how the constraints coming from the angular analysis of B s → ϕee at low q 2 should be interpreted in the presence of mixing.