Search for $D^0\to {\hat{I}}^3{\hat{I}}^3$ and improved measurement of the branching fraction for $D^0\to \ddot{I}{€}^0\ddot{I}{€}^0$

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 $D^0\to {\hat{I}}^3{\hat{I}}^3$ using a double-tag technique. We find no signal and set an upper limit at $90\%$ confidence level for the branching fraction of $B(D^0\to {\hat{I}}^3{\hat{I}}^3)<3.8\times 10^{-6}$. We also investigate $D^0$-meson decay into two neutral pions, obtaining a branching fraction of $B(D^0\to \ddot{I}{€}^0\ddot{I}{€}^0)=(8.24\pm 0.21(\text{stat.})\pm 0.30(\text{syst.}))\times 10^{-4}$, the most precise measurement to date and consistent with the current world average

Minor revisions, version published in Physical Review D