Search for $D^0\to\gamma\gamma$ and improved measurement of the branching fraction for $D^0 \to \pi^0\pi^0$

TL;DR

This paper reports a search for the rare decay $D^0\to\gamma\gamma$ with no observed signal, setting an upper limit, and provides the most precise measurement to date of the branching fraction for $D^0\to\pi^0\pi^0$, improving our understanding of charm meson decays.

Contribution

The study presents the first upper limit on $D^0\to\gamma\gamma$ decay and the most precise measurement of $D^0\to\pi^0\pi^0$ branching fraction to date.

Findings

No signal observed for $D^0\to\gamma\gamma$, upper limit set at $3.8\times10^{-6}$.

Precise measurement of $D^0\to\pi^0\pi^0$ branching fraction: $(8.24\pm0.21\text{(stat.)}\pm0.30\text{(syst.)})\times10^{-4}$.

Results are consistent with current world averages.

Abstract

Using $2.92$ fb$^{-1}$ of electron-positron annihilation data collected at $\sqrt{s} = 3.773$~GeV with the BESIII detector, we report the results of a search for the flavor-changing neutral current process $D^0\to\gamma\gamma$ using a double-tag technique. We find no signal and set an upper limit at $90\%$ confidence level for the branching fraction of $B(D^0\to\gamma\gamma) < 3.8\times10^{-6}$. We also investigate $D^0$-meson decay into two neutral pions, obtaining a branching fraction of $B(D^0\to\pi^0\pi^0) = (8.24\pm0.21(\text{stat.})\pm0.30(\text{syst.}))\times10^{-4}$, the most precise measurement to date and consistent with the current world average