CP Violation and New Physics in $B_s$ Decays

The $B_s$-meson system is a key element in the $B$-physics programme of hadron colliders, offering various avenues to explore CP violation and to search for new physics. One of the most prominent decays is $B_s\to J/\psi\phi$,thecounterpartof$B_d\to J/\psi K_S$, providing a powerful tool to search for new-physics contributions to $B_s^0$–$\overline{B_s^0}$ mixing. Another benchmark mode is $B_s\to K^{+}{K}^{-}$, which complements $B_d\to {\pi }^{+}{\pi }^{-}$, thereby allowing an extraction of the angle $\gamma$ of the unitarity triangle that is sensitive to new-physics effects in the QCD penguin sector. Finally, we discuss new methods to constrain and determine $\gamma$ with the help of $B_s\to D_s^{(\ast )\pm }{K}^{\mp }$ decays, which complement $B_d\to D^{(\ast )\pm }{\pi }^{\mp }$ modes. Since these strategies involve ``tree’’ decays, the values of $\gamma$ thus extracted exhibit a small sensitivity on new physics.