Thesis BELLE2-MTHESIS-2021-068

Sensitivity Study of $B^{+}\rightarrow \mu^{+}\nu$ in the Belle II Experiment

Yen-Ting Chin ; Pao-Ti Chang

2021
National Taiwan University Taipei, Taiwan

Abstract: In this study, we intend to estimate the statistical significance of $B^{+}\rightarrow \mu^{+}\nu$ when various amounts of Belle II data are available in the future, assuming that the Standard Model estimation of the branching fraction of $B^{+}\rightarrow \mu^{+}\nu$ is correct. The Monte­ Carlo method is applied to generate a large amount of data samples to simulate the physics events produced by $e^{+}e^{-}$ collision on the center­-of­-mass energy of 10.58 GeV in the SuperKEKB accelerator. These physics events include the $e^{+}e^{-} \rightarrow q\bar{q}$, the $e^{+}e^{-} \rightarrow \tau^{+}\tau^{-}$ , and the $e^{+}e^{-} \rightarrow \Upsilon(4S) \rightarrow B^{0}\bar{B^{0}}/B^{+}B^{-}$ processes. The Belle II detector responses to these physics events are also simulated. In this study, we use multivariate analysis to distin­guish the $B^{+}\rightarrow \mu^{+}\nu$ events from the background events. We establish probability den­sity functions for different physics processes and generate Asimov data sets. We then use the profile likelihood function of the Asimov data sets to estimate the statistical signifi­cance of $B^{+}\rightarrow \mu^{+}\nu$ when different amounts of Belle II data are available. According to the estimation, we will need to collect more than 7 $ab^{-1}$ of data in order to surpass the significance of $5\sigma$ in order to claim the discovery of $B^{+}\rightarrow \mu^{+}\nu$.

Note: Presented on 25 01 2021
Note: MSc

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