Radiative decays of B mesons at LHCb

This thesis is dedicated to the study of radiative decays of $B$ mesons at LHC$b$. At quark level, such decays are a $b\to s\gamma$ transition and take place via a penguin loop and are sensitive to virtual contribution of New Physics, which can be indicated by an increase in the decay rates. These decays also offer the possibility to test the V-A structure of the Standard Model coupling in the processes mediated by loop penguin diagrams. In the decay $B_s \to \phi\gamma$, New Physics contribution can be probed by measuring the polarization of the photon in this decay. Systematic effects in the proper time reconstruction of the $B_s$ in $B_s \to \phi\gamma$ can bias the photon polarization measurement in this decay, which will reduce the sensitivity on the relevant New Physics parameter. The author studied those effects and developed ideas to calibrate them using $B_d\to K^{*}\gamma$ and $B_s\to J/\psi\phi$ decays as control channels. These studies are mostly Monte Carlo based due to a relatively small data set from the 2010 running. However, some studies and cross checks have indeed been performed with data. The author developed the trigger and stripping (another level of skimming the data, after the trigger) selections for $B_s\to \phi\gamma$ and $B_d\to K^{*}\gamma$ decays, and made a major contribution to the selection of the first significant sample of $B_d\to K^{*}\gamma$ from the 2010 data set of LHC$b$.