Search for the massless dark photon with $D^0\toωγ'$ and $D^0\toγγ'$

Abstract

Using $7.9\mathrm{f}{\mathrm{b}}^{-1}$ 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 $D^0\toωγ'$ and $D^0\toγγ'$ 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 $1.1\times 10^{-5}$ and $2.0\times 10^{-6}$ for $D^0\toωγ'$ and $D^0\toγγ'$, respectively. These results provide the most stringent constraint on the new physics energy scale associated with $cuγ'$ coupling in the world, with the new physics energy scale related parameter $|\mathbb{C}{|}^2+|{\mathbb{C}}_5{|}^2<8.2\times 10^{-17}{\mathrm{GeV}}^{-2}$ at the 90% confidence level.

10 pages, 3 figures