The Standard Model confronts CP violation in $D^0 \to \pi^+\pi^-$ and $D^0 \to K^+K^-$

TL;DR

This paper examines the recent measurements of CP asymmetries in D0 decays to pions and kaons, analyzing whether these observations align with Standard Model predictions or suggest new physics, considering SU(3) breaking and rescattering effects.

Contribution

It provides a comprehensive analysis of CP violation in D0 decays within the Standard Model, highlighting the roles of SU(3) breaking and rescattering, and assesses the compatibility of measurements with theoretical expectations.

Findings

Measured asymmetries are marginally compatible with the Standard Model.

Large SU(3) breaking and rescattering effects are implied by the data.

Improved experimental precision could reveal signs of new physics.

Abstract

The recently measured direct CP asymmetries in the processes $D^0\to \pi^+\pi^-$ and $D^0\to K^+K^-$ show a significant deviation from the naive Standard Model expectation. Using a general parameterization of the decay amplitudes, we show that the measured branching ratios imply large SU(3) breaking and large violations of the naive $1/N_c$ counting. Furthermore, rescattering constrains the I=0 amplitudes in the $\pi\pi$ and $KK$ channels. Combining all this information, we show that, with present errors, the observed asymmetries are marginally compatible with the Standard Model. Improving the experimental accuracy could lead to an indirect signal of new physics.