Shedding light on CP violation in the charm system via D to V gamma decays

TL;DR

This paper explores how new physics models with CP-violating dipole operators could produce observable CP asymmetries in radiative charm decays, offering potential signals beyond the Standard Model.

Contribution

It demonstrates that CP violation in D to V gamma decays can be significantly enhanced by new physics, providing a novel way to detect physics beyond the Standard Model.

Findings

CP asymmetries of several percent are possible in D to P+ P- gamma decays.

Enhanced electromagnetic dipole matrix elements can offset long-distance effects.

Observation of such asymmetries would indicate new physics involving dipole operators.

Abstract

Recent evidence for direct CP violation in non-leptonic charm decays cannot be easily accommodated within the Standard Model (SM). On the other hand, it fits well in new physics models generating CP violating Delta C=1 chromomagnetic dipole operators. We show that in these frameworks sizable direct CP asymmetries in radiative D to P+ P- gamma decays (P=pi,K), with M_PP close to the rho or the phi peak, can be expected. Enhanced matrix elements of the electromagnetic dipole operators can partly compensate the long distance dominance in these decays, leading to CP asymmetries of the order of several percent. If observed at this level, these would provide a clean signal of physics beyond the SM and of new dynamics associated to dipole operators. We briefly comment on related CP violating observables accessible via time dependent D(Dbar) to P+ P- gamma studies and angular decay product distributions in rare semileptonic D decays.