Search for the rare decay $D^0\to\gamma\gamma$ at Belle

TL;DR

This paper reports a search for the rare decay $D^0\to\gamma\gamma$ using Belle data, setting the most restrictive upper limit to date, with no significant signal observed.

Contribution

The study provides the most stringent upper limit on the branching fraction of $D^0\to\gamma\gamma$, improving constraints on new physics models.

Findings

No significant signal detected.

Upper limit on branching fraction set at $8.5\times10^{-7}$.

Most restrictive limit to date.

Abstract

We search for the rare radiative decay $D^0\to\gamma\gamma$ using a data sample with an integrated luminosity of $832{\rm fb^{-1}}$ recorded by the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. We find no statistically significant signal and set an upper limit on the branching fraction of ${\cal B}(D^0\to\gamma\gamma)<8.5\times10^{-7}$ at $90\%$ confidence level. This is the most restrictive limit on the decay channel to date.