Sumitted to PubDB: 2023-04-25

Category: Phd Thesis, Visibility: Public

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Authors	Tadeas Bilka, Zdenek Dolezal
Date	2022-01-01
Belle II Number	BELLE2-PTHESIS-2023-006
Abstract	This thesis deals with two independent yet closely related topics. In the first part, a measurement of branching fraction and time-dependent $CP$ violation in $B^0\to {\eta }_c{K}_S^0$, ${\eta }_c\to K_S^0{K}^{\pm }{\pi }^{\mp }$ decays is performed. This decay allows access to $\sin 2{\varphi }_1$, where ${\varphi }_1$ is an angle of the unitary triangle of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. The measurement is based on the entire dataset of the Belle experiment, which consists of $772\times {10}^6$ $B$ meson pairs collected at the KEKB $e^{+}{e}^{-}$ collider. The extracted mixing-induced and direct $CP$-violation parameters read $\sin 2{\varphi }_1\simeq \mathcal{S}=0.59\pm 0.17(\mathrm{stat})\pm 0.07(\mathrm{syst})$ and $\mathcal{A}=0.16\pm 0.12(\mathrm{stat})\pm 0.06(\mathrm{syst})$, respectively. The measured product of branching fractions $\mathcal{B}(B^0\to {\eta }_c{K}_S^0)\times \mathcal{B}({\eta }_c\to K_S^0{K}^{\pm }{\pi }^{\mp })$ is $(9.8\pm 0.6(\mathrm{stat})\pm 0.4(\mathrm{syst})\pm 2.3(\mathrm{int}))\times {10}^{-6}$, where the last uncertainty accounts for interference with non-resonant background. The second part deals with the alignment of the vertex detector and the central drift chamber of the Belle~II experiment at the SuperKEKB collider, which is a next-generation Super-B-Factory. With the new pixel detector and the presented alignment method, Belle~II achieves approximately twice better impact parameter resolutions than Belle. The presented alignment procedure involves a simultaneous determination of about sixty thousand parameters and accounts for time-dependent detector instabilities. The method is evaluated in simulations, and its performance is validated using data recorded by the Belle~II detector and in the first world-leading physics measurements.
Conference	Prague

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