Sagar Hazra ; Gagan Mohanty

2024
Tata Institute of Fundamental Research Mumai, India

Abstract: The $\Bz\to\KS\piz$ 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 $\CP$ violation asymmetry in this neutral $B$-meson decay channel as an important consistency test of the standard model. We perform a measurement of the $\CP$-violating parameters $\ACP$ and $\SCP$ in $\Bz\to\KS\pi^0$ at Belle II using a sample of $387\times 10^{6}$ $\BBbar$ events recorded in $\ep\en$ collisions at a center-of-mass energy corresponding to the $\Upsilon(4S)$ resonance. These parameters are determined by fitting the proper decay-time distribution of a sample of 415 signal events. We obtain $\mathcal{B}=(11.15^{+0.69}_{-0.67} \pm 0.61)\times 10^{-6}$, $\ACP = -0.04^{+0.14}_{-0.15}\pm 0.05$ and $\SCP = 0.75^{+0.20}_{-0.23}\pm 0.04$, 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 $D^{*+}\to D^{0}(\to K^{-}\pi^{+})\pi^{+}$ decay samples. The introduction of additional information from the SVD is found to improve the overall PID performance in the low momentum region.

Note: Presented on 23 02 2024
Note: PhD