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PoS(CKM2016)134

CP asymmetries in $D$ decays to two pseudoscalars

U. Nierste, S. Schacht

in 9th International Workshop on the CKM Unitarity Triangle

Contribution: pdf

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
$a_{CP}^{\mathrm{dir}}(D^+\rightarrow
\bar{K}^0K^+)$, $a_{CP}^{\mathrm{dir}}(D_s^+\rightarrow
K^0\pi^+)$, 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.