On CP Asymmetries in Two-, Three- and Four-Body D Decays

TL;DR

This paper reviews CP asymmetries in D meson decays, exploring potential signals of New Dynamics and their detection prospects at current and future experiments, with a focus on T asymmetries and interference effects.

Contribution

It provides a comprehensive discussion on CP asymmetries in D decays, including predictions for inclusive and exclusive asymmetries and the role of New Dynamics in these processes.

Findings

Evidence for direct CP asymmetry in D^0 decays at 3.5 sigma.

Analysis of T asymmetries in D to h_1 h_2 l^+ l^- decays.

Potential to detect New Dynamics effects at LHCb and Super-Flavour Factories.

Abstract

Indirect and direct CP violations have been established in K_L and B_d decays. They have been found in two-body decay channels -- with the exception of K_L to pi^+ pi^- e^+ e^- transitions. Evidence for direct CP asymmetry has just appeared in LHCb data on A_{CP}(D^0 to K^+ K^-) - A_{CP}(D^0 to pi^+ pi^-) with 3.5 sigma significance. Manifestations of New Dynamics (ND) can appear in CP asymmetries just below experimental bounds. We discuss D^{\pm}_{(s)}, D^0/\bar D^0 and D_L/D_S transitions to 2-, 3- and 4-body final states with a comment on predictions for inclusive vs. exclusive CP asymmetries. In particular we discuss T asymmetries in D to h_1 h_2 l^+ l^- in analogy with K_L to pi^+ pi^- e^+ e^- transitions due to interference between M1, internal bremsstrahlung and possible E1 amplitudes. Such an effect depends on the strength of CP violation originating from the ND -- as discussed here for Little Higgs Models with T parity and non-minimal Higgs sectors -- but also in the interferences between these amplitudes even in the Standard Model (SM). More general lessons can be learnt for T asymmetries in non-leptonic D decays like D to h_1h_2 h_3 h_4. Such manifestations of ND can be tested at LHCb and other Super-Flavour Factories like the projects at KEK near Tokyo and at Tor Vergata/Frascati near Rome.