LHCb: Measurement of the ratio of branching fractions $\mathcal{B}(B \to \gamma)/\mathcal{B}(B_s \to \phi\gamma)$ at LHCb

Rare radiative decays of the B-mesons may provide a good test for the Standard Model. Being forbidden at tree level, such processes may only occur due to loop diagrams involving FCNC and thus become very sensitive to the impact of new non-standard particles. This impact may be discovered through different observables, like branching fractions, isospin asymmetries, photon polarization etc., and the accuracy of the theoretical predictions for such decays makes them attractive from the experimental point of view. Having started to take data at an energy of $\sqrt{s}$ = 7 Tev since 2010, by mid-summer of 2011 LHCb has collected 340 pb$^{-1}$ of integrated luminosity. With these data clear signals for $B_d \to K^*\gamma$ and $B_s \to \phi\gamma$ have been observed. The ratio of branching fractions of these decays has been measured with good accuracy and it is consistent with the theoretical predictions and previous experimental results.