KEK-PH Lectures and Workshops 2020

Flavor Physics at Future Z-Factories: b→sττ Measurements and Beyond

5 Aug 2020, 14:30

20m

KEK-PH collider

Speaker

Dr Lingfeng Li (HKUST)

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 $R_{D^{(\ast )}}$ 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, $B^0\to K^{\ast 0}{\tau }^{+}{\tau }^{-}$, $B_s\to \varphi {\tau }^{+}{\tau }^{-}$, $B^{+}\to K^{+}{\tau }^{+}{\tau }^{-}$ 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.