Search for $\mathrm{B}^+ \to \mathrm{K}^{*+}\tau^+\tau^-$ with hadronic tagging at the Belle II Experiment

In recent years, intriguing hints for violation of lepton flavor universality have been accumulated in semileptonic $B$ decays with the help of multiple experiments. 

The flavor-changing neutral current process $b \to s \tau^+\tau^-$ is particularly sensitive to New Physics models which couples to the third generation, or with couplings proportional to the particle mass. Some theoretical models allow for an increase in the branching fraction of up to three orders of magnitude compared to the Standard Model prediction, which is within the observable experimental range of the Belle~II experiment. 

This thesis presents the status of the first search for $B^+ \to K^{*+}\tau\tau$ decays along with a first estimate on the signal sensitivity. In reconstruction, hadronic tagging is employed where the corresponding $B$ meson partner in $\Upsilon$(4S) decays is reconstructed in a variety of hadronic decay chains to increase the selection purity.