Search for the Rare Decay $B^+ \to \ell^+ \nu_{\ell} \gamma$ with the Full Event Interpretation at the Belle II Experiment

The ${e^+e^-}$ collider experiment Belle II at the SuperKEKB accelerator in Japan produces charged and neutral B-meson pairs whose decays offer a great variety of analyses including the rare decay $B^+ \to \ell^+ \nu_{\ell} \gamma$. Although no B-factory has yet to observe this decay, the existing measurements provide an important limit on the first inverse momentum $\lambda_{\mathrm{B}}$ of the light-cone distribution amplitude (LCDA) of the B-meson. This thesis presents a simultaneous analysis of $B^+ \to \ell^+ \nu_{\ell} \gamma$ and $B^+ \to \pi^0 \ell^+ \nu_{\ell}$ decays with the Full Event Interpretation tagging algorithm. The analysis is validated with a Belle II data set according to an integrated luminosity of $\mathcal{L}=63.25 fb^{-1}$.