Rare Decay D 0 →γγ*

Abstract

We present a calculation of the rare decay mode D 0 → γγ, in which the long distance contributions are expected to be dominant. Using the heavy quark chiral Lagrangian with a strong g coupling as recently determined by CLEO from the D* → Dπ width, we consider both the anomaly contribution that relates to the annihilation part of the weak Lagrangian and the one-loop π,K diagrams. The loop contributions, which are proportional to g and contain the a 1 Wilson coefficient, are found to dominate the decay amplitude, which turns out to be mainly parity violating. The branching ratio is then calculated to be (1.0±0.5)×10 -8 . The observation of an order of magnitude larger branching ratio could be indicative of new physics.