Moritz Gelb

13 March 2018

Abstract: The Belle collaboration reported an upper limit on the partial branching fraction on the rare decay $\mathrm{B}^+ \to \ell^+ \nu_{\ell} \gamma$ using the full dataset recorded at the $\mathrm{\Upsilon(4S)}$ resonance. The decay allows for the extraction of the first inverse momentum of the light-cone distribution amplitude, an important parameter for QCD factorization for non-leptonic $\mathrm{ B} $ decays. We present a MC study applying an improved tagging algorithm developed for the Belle~II experiment. We observe an increase of signal reconstruction efficiency of a factor of three, improving the expected sensitivity to $ 3.8\sigma $. Further we give an outlook for the sensitivity measuring $\mathrm{B}^+ \to \ell^+ \nu_{\ell} \gamma$ with the Belle~II experiment.