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

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 $B(D^0\to \gamma \gamma )<3.8\times 10^{-6}$. We also investigate $D^0$-meson decay into two neutral pions, obtaining a branching fraction of $B(D^0\to {\pi }^0{\pi }^0)=(8.24\pm 0.21(\text{stat.})\pm 0.30(\text{syst.}))\times 10^{-4}$, the most precise measurement to date and consistent with the current world average

Minor revisions, version published in Physical Review D

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