Sumitted to PubDB: 2024-03-11

Category: Phd Thesis, Visibility: Public

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Authors	Sagar Hazra, Gagan Mohanty
Date	2024-01-01
Belle II Number	BELLE2-PTHESIS-2024-004
Abstract	The $\text{Bz}\to \text{KS}\text{piz}$ decay is dominated by $b\to s$ loop amplitudes. Such flavor-changing-neutral-current transitions are highly suppressed in the standard model and provide an indirect route to search for new physics. The excellent neutral-particle reconstruction capability of Belle~II allows a unique measurement of $\text{CP}$ violation asymmetry in this neutral $B$-meson decay channel as an important consistency test of the standard model. We perform a measurement of the $\text{CP}$-violating parameters $\text{ACP}$ and $\text{SCP}$ in $\text{Bz}\to \text{KS}{\pi }^0$ at Belle II using a sample of $387\times {10}^6$ $\text{BBbar}$ events recorded in $\text{ep}\text{en}$ collisions at a center-of-mass energy corresponding to the $\mathrm{{\rm Y}}(4S)$ resonance. These parameters are determined by fitting the proper decay-time distribution of a sample of 415 signal events. We obtain $\mathcal{B}=({11.15}_{-0.67}^{+0.69}\pm 0.61)\times {10}^{-6}$, $\text{ACP}=-{0.04}_{-0.15}^{+0.14}\pm 0.05$ and $\text{SCP}={0.75}_{-0.23}^{+0.20}\pm 0.04$, where the first uncertainties are statistical and the second are systematic. In the latter part, we report a particle identification (PID) framework developed based on ionization energy loss information in the silicon-strip vertex detector (SVD) of Belle II for charged pions and kaons using $D^{\ast +}\to D^0(\to K^{-}{\pi }^{+}){\pi }^{+}$ decay samples. The introduction of additional information from the SVD is found to improve the overall PID performance in the low momentum region.
Conference	Mumai, India

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