Thesis BELLE2-PTHESIS-2023-006

Time-dependent CP violation in $B^0 \to \eta_c K^0_S$ decays at the Belle experiment, Alignment of the Belle II detector

Tadeas Bilka ; Zdenek Dolezal

Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University Prague

Abstract: This thesis deals with two independent yet closely related topics. In the first part, a measurement of branching fraction and time-dependent $C\!P$ 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 $\sin 2 \phi_1$, where $\phi_1$ 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 $C\!P$-violation parameters read $\sin 2\phi_1 \simeq \mathcal{S} = 0.59 \pm 0.17~\mathrm{(stat)} \pm 0.07~\mathrm{(syst)}$ and $\mathcal{A}=0.16\pm0.12~\mathrm{(stat)}\pm0.06~\mathrm{(syst)}$, 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 $(9.8\pm0.6~\mathrm{(stat)}\pm0.4~\mathrm{(syst)}\pm2.3~\mathrm{(int)})\times 10^{-6}$, 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.

Note: Presented on 01 11 2022
Note: PhD

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 Record created 2023-04-25, last modified 2023-04-25

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