Measurements of the absolute branching fractions of $D^0\to \gamma {\bar{K}}^{\ast 0}$ and $D^0\to \gamma \varphi$

Abstract

By analyzing a sample of 20.3 fb${}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we have made a first measurement of the absolute branching fractions of the radiative decays $D^0\to \gamma {\bar{K}}^{\ast 0}$ and $D^0\to \gamma \varphi$ to be $(3.81\pm 0.18_{stat.}\pm 0.20_{syst.})\times 10^{-4}$ and $(2.51\pm 0.44_{stat.}\pm 0.11_{syst.})\times 10^{-5}$, respectively. The statistical significances of $D^0\to \gamma {\bar{K}}^{\ast 0}$ and $D^0\to \gamma \varphi$ are $26.8\sigma$ and $7.9\sigma$, respectively. The obtained branching fractions are consistent with the corresponding world average values. In addition, the measured $CP$ asymmetry ${\mathcal{A}}_{CP}(D^0\to \gamma {\bar{K}}^{\ast 0})=(-0.7\pm 5.0_{stat.}\pm 4.1_{syst.})\%$ is consistent with $CP$ conservation.