Exploiting the width difference in Bs→ϕγ

The photon polarization in B→Vγ is a sensitive probe of right-handed currents. In the time dependent decay rate of Bs→ϕγ the coefficients S and H in front of the sin(Δmst) and the sinh(ΔΓs/2t) terms are sensitive to those right-handed currents. As compared to the Bd system there is a sizable width difference in Bs mesons which leads to the additional measurable observable H. We show with a Monte Carlo simulation that the expected resolution on S and H will be about 0.15 at the LHCb experiment for ΔΓs/Γs=0.15 and a data sample of 2 fb−1. We also show that the observable H can be measured from the untagged decay rate of Bs mesons which has considerable experimental advantages as no flavour tag will be required. The resolution on H is inversely proportional to the Bs width difference ΔΓs. These experimental prospects have to be compared with the Standard Model predictions Sϕγ=0±0.002 and Hϕγ=0.047±0.025+0.015 presented in this Letter. We also give the Standard Model prediction and the experimental sensitivity for the direct CP asymmetry in Bs→ϕγ.