CP asymmetries in $D\to P{P}^{\prime }$ decays

Abstract

This talk addresses two topics related to CP asymmetries in $D$ meson decays to two pseudoscalar mesons. First I discuss how new physics can be distinguished from the Standard Model through two sum rules relating three direct CP asymmetries each, using the sum rule correlating $D^0\to K^{+}{K}^{-}$, $D^0\to {\pi }^{+}{\pi }^{-}$, and $D^0\to {\pi }^0{\pi }^0$ for illustration. The other sum rule involves $a_{CP}^{\mathrm{dir}}(D^{+}\to {\bar{K}}^0{K}^{+})$, $a_{CP}^{\mathrm{dir}}(D_s^{+}\to K^0{\pi }^{+})$, and $a_{CP}^{\mathrm{dir}}(D_s^{+}\to K^{+}{\pi }^0)$. The second topic is the direct CP asymmetry in the decay $D^0\to K_S{K}_S$, which is expected to be large in the Standard Model for two reasons: Flavor-SU(3) symmetry suppresses the tree amplitude which enhances the crucial "penguin-to-tree" ratio and the "penguin" amplitude is dominated by the tree-level $W$ boson exchange between $c$ and $u$ quarks. We find that $|a_{CP}^{\mathrm{dir}}(D^0\to K_S{K}_S)|$ can be as large as $1.1\%$ in the Standard Model. We advocate $D^0\to K_S{K}_S$ as a discovery channel for charm CP violation.

Comments: Talk at ICHEP2016, 3-10 August 2016, Chicago, USA, and CKM2016, 28 November - 3 December 2016, Tata Institute for Fundamental Research (TIFR), Mumbai, India