Speaker
Description
$b\to s\tau^+\tau^-$ measurements are highly motivated for addressing lepton-flavor-universality(LFU)-violating puzzles such as $R_{K^{(\ast)}}$ anomalies. The anomalies of $R_{D^{(*)}}$ and $R_{J/\psi}$ further strengthen their necessarity and significance, given that the LFU-violating hints from both involve the third-generation leptons directly. $Z$ factories of future $e^-e^+$ colliders stand at a great position to conduct such measurements, because of their relatively high production rates and reconstruction efficiency for $B$ mesons at $Z$ pole. To fully explore this issue, we pursue a sensitivity study for four $b\to s\tau^+\tau^-$ benchmark channels, namely, $B^0\to K^{\ast 0} \tau^+ \tau^-$, $B_s\to\phi \tau^+ \tau^-$, $B^+ \to K^+ \tau^+ \tau^- $ and $B_s \to \tau^+ \tau^-$, at the future $Z$ factories. A scheme of $B$-meson reconstruction mainly based on detector tracking system is developed for this purpose. The simulations indicate that at Tera-$Z$ the branching ratios of the first three channels can be measured with a precision of $\mathcal O(10^{-7})$ and that of $B_s \to \tau^+ \tau^-$ with a precision of $\mathcal O(10^{-5})$. The interpretation of these results in effective field theory is presented.
