Search for the massless dark photon with $D^0\to\omega\gamma'$ and $D^0\to\gamma\gamma'$

TL;DR

This study searches for a massless dark photon via rare $D^0$ decays using BESIII data, setting new upper limits on the branching fractions and constraining new physics energy scales related to $cu ext{ extbackslash}gamma'$ coupling.

Contribution

First experimental search for massless dark photon in $D^0$ decays, establishing the most stringent constraints on related new physics parameters.

Findings

No significant dark photon signals observed.

Upper limits on branching fractions set at $1.1\times10^{-5}$ and $2.0\times10^{-6}$.

New physics energy scale parameter constrained to $<8.2\times10^{-17}~\rm{GeV}^{-2}$.

Abstract

Using $7.9~\rm{fb^{-1}}$ of $e^+e^-$ collision data collected at $\sqrt{s}=3.773$ GeV with the BESIII detector at the BEPCII collider, we search for the massless dark photon with the flavor-changing neutral current processes $D^0\to\omega\gamma'$ and $D^0\to\gamma\gamma'$ for the first time. No significant signals are observed, and the upper limits at the 90% confidence level on the massless dark photon branching fraction are set to be $1.1\times10^{-5}$ and $2.0\times10^{-6}$ for $D^0\to\omega\gamma'$ and $D^0\to\gamma\gamma'$, respectively. These results provide the most stringent constraint on the new physics energy scale associated with $cu\gamma'$ coupling in the world, with the new physics energy scale related parameter $|\mathbb{C}|^2+|\mathbb{C}_5|^2<8.2\times10^{-17}~\rm{GeV}^{-2}$ at the 90% confidence level.