Daniel Jacobi ; Prof. Dr. Jochen Dingfelder ; Dr. Peter Lewis ; Svenja Katharina Granderath

2021
Physikalisches Institut Bonn

Abstract: In this thesis the rare $B \to \mu \nu_{\mu}$ decay was investigated using the inclusive tagging approach. The reconstruction of the tag side $B$ meson kinematics is deteriorated by multiple factors, which were investigated by studying the different reconstruction errors. Measures were employed to improve the reconstruction, but many reconstruction errors cannot be avoided and are due to the physical properties of the Belle II detector. A different approach was taken to improve the estimation of the $B_{\text{tag}}$ kinematics. Starting with applying the method of constraining, calibrating and optimizing the $p_z$ component of $B_{\text{tag}}$ which was previously used at Belle, novel methods were developed. In order to compare two different methods, a fit to an Asimov data set was performed for each method and the statistical significances were compared. A calibration of the $p_x$, $p_y$ and $p_z$ component, as well as a calibration in bins of $N_{\text{lep}}$ and $\theta_{\text{ROE}}$ has not led to the desired increase in significance. The method of the neutrino estimation was investigated and showed a small increase in the significance compared to the method used by the Belle analysis. Additional methods were also presented. The neutrino estimation method was used for further considerations. The fit stability was validated by fitting the MC samples to 1000 generated toy distributions and observing the obtained pull distributions. A significance estimation was employed in order to assess the integrated luminosity needed to observe and discover the $B \to \mu \nu_{\mu}$ decay at Belle II.

Note: Presented on 25 08 2021
Note: MSc