Radiative decays at LHCb

Abstract

The radiative decay Lambda_b -> Lambda gamma is observed for the first time using a data sample of proton-proton collisions corresponding to an integrated luminosity of 1.7 1/fb collected by the LHCb experiment at a center-of-mass energy of 13 TeV. Its branching fraction is measured to be B(Lambda_b -> Lambda gamma) = (7.1 +- 1.5 +- 0.6 +- 0.7) 10^{-6}, where the quoted uncertainties are statistical, systematic and systematic from external inputs, respectively. A time-dependent analysis of the Bs -> phi gamma decay rate is performed to determine the CP-violating observables S and C, and the mixing-induced observable Adelta. The measurement is based on a sample of pp collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3 1/fb at center-of-mass energies of 7 and 8 TeV. The measured values are S= 0.43 +- 0.30 +- 0.11, C= 0.11 +- 0.29 +- 0.11, Adelta = -0.67 +0.37 -0.41 +- 0.17, where the first uncertainty is statistical and the second systematic. The results are consistent with the Standard Model predictions.