Speaker
Description
The $b \to s\gamma$ is a critical FCNC process that could be used to probe CP violation (CPV) and New Physics (NP), especially in the context of future Z factory. The Circular Electron-Positron Collider (CEPC) offers inherent advantages for studying flavor physics, as it offers high statistic, clean collision environment, and superior detector performance. We quantify the anticipated precision of $B_s^0 \to \phi\gamma$ measurement at the CEPC Z pole modes, showing its signal strength could be determined to a relative accuracy of 0.16%, enhanced by roughly two orders of magnitudes compared to existing measurements. Additionally, we conduct a time dependent analysis of the $B_s^0 \to \phi\gamma$ decay, accounting for $B_s^0/\bar{B}_s^0$ mixing oscillations, and extract the mixing-induced and CP-violating parameters ${\mathcal{A}_{\phi\gamma}^\Delta}$, ${C_{\phi\gamma}}$ and ${S_{\phi\gamma}}$. The result are
$$ \begin{align*} {\mathcal{A}_{\phi\gamma}^\Delta} &= -0.67 \pm 0.0283(\text{stat}) \pm 0.0408(\text{syst}), \\ {C_{\phi\gamma}} &= 0.11 \pm 0.097(\text{stat}) \pm 0.0092(\text{syst}), \\ {S_{\phi\gamma}} &= 0.34 \pm 0.095(\text{stat}) \pm 0.0384(\text{syst}). \end{align*} $$
We also conduct a relative detector optimization study by establishing the correlation between the anticipated precision and the intrinsic resolution of the ECAL, as well as the performance of the PID system.
