SU(3) symmetry breaking and CP violation in D -> PP decays

TL;DR

This paper investigates CP violation in D meson decays to two pseudoscalar particles, analyzing SU(3) symmetry breaking effects, predicting CP asymmetries, and exploring new physics scenarios to explain recent experimental observations.

Contribution

It provides a detailed analysis of flavor SU(3) symmetry breaking and CP violation in D -> PP decays, incorporating QCD factorization and phenomenological fits, and proposes methods to distinguish new physics models.

Findings

Predicted direct CP asymmetry difference between D0 -> K+K- and D0 -> pi+pi- is about -0.14% to -0.15%.

CP asymmetry in D0 -> K0 K0bar ranges from -0.62 to -1.82 per mille.

Predictions for branching fractions are improved over SU(3) symmetry limit.

Abstract

Evidence of CP violation in the charm sector has been observed recently by the LHCb and CDF Collaborations. Adopting the topological diagram approach, we study flavor SU(3) symmetry breaking effects in the weak decay tree amplitudes of singly Cabibbo-suppressed $D\to PP$ decays. The symmetry breaking in the color-allowed and color-suppressed amplitudes is estimated with the help of the factorization ansatz, while that in the $W$-exchange amplitude is done by fitting to related branching fraction data. We find that the $W$-exchange amplitudes stay in the second quadrant relative to the color-allowed tree amplitude, albeit there are two possibilities for one type of $W$-exchange amplitude. The weak decay penguin amplitudes, on the other hand, are evaluated within the framework of QCD factorization. Using the input of topological tree amplitudes extracted from the Cabibbo-favored decay modes and the perturbative results for QCD penguin amplitudes, we make predictions for the branching fractions and CP asymmetries of singly Cabibbo-suppressed modes. The predictions of branching fractions are generally improved from those in the SU(3) limit. We conclude that the direct CP asymmetry difference between $D^0 \to K^+ K^-$ and $D^0 \to \pi^+ \pi^-$ is about $-(0.139\pm 0.004)%$ and $-(0.151\pm 0.004)%$ for the two solutions of $W$-exchange amplitudes, respectively. We also find that the CP asymmetry of $D^0\to K^0\ov K^0$ dominated by the interference between $W$-exchange amplitudes ranges from $-0.62\times 10^{-3}$ to $-1.82\times 10^{-3}$. We study phenomenological implications of two new physics scenarios for explaining the observed CP asymmetry in the charm sector, one with large penguin amplitudes and the other with a large chromomagnetic dipole operator. We find that the two scenarios can be discriminated by the measurements of CP asymmetries of a set of decay modes.