Radiative three-body D-meson decays in and beyond the standard model

TL;DR

This paper analyzes radiative D-meson decays using QCD frameworks, highlighting their potential to test the Standard Model and probe new physics through decay rates, asymmetries, and Dalitz plot features.

Contribution

It compares QCD factorization and chiral perturbation theory predictions for D-meson radiative decays, proposing observables to distinguish decay mechanisms and search for new physics.

Findings

Branching ratios are around 10^{-3} for K pi gamma modes.

Dalitz plots and asymmetries differ significantly between frameworks.

Decays are accessible to BES III and Belle II experiments.

Abstract

We study radiative charm decays $D \to P_1 P_2 \gamma$, $P_{1,2}=\pi,K$ in QCD factorization at leading order and within heavy hadron chiral perturbation theory. Branching ratios including resonance contributions are around $\sim 10^{-3}$ for the Cabibbo-favored modes into $K \pi \gamma$ and $\sim 10^{-5}$ for the singly Cabibbo-suppressed modes into $\pi^+ \pi^- \gamma, K^+ K^- \gamma$, and thus in reach of the flavor factories BES III and Belle II. Dalitz plots and forward-backward asymmetries reveal significant differences between the two QCD frameworks; such observables are therefore ideally suited for a data-driven identification of relevant decay mechanisms in the standard-model dominated $D \to K \pi \gamma$ decays. This increases the potential to probe new physics with the $D \to \pi^+ \pi^- \gamma$ and $D \to K^+ K^- \gamma$ decays, which are sensitive to enhanced dipole operators. CP asymmetries are useful to test the SM and look for new physics in neutral $|\Delta C|=1$ transitions. Cuts in the Dalitz plot enhance the sensitivity to new physics due to the presence of both $s$- and $t,u$-channel intermediate resonances.