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

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 $D^0\to \gamma \phi$ to be $(3.81\pm {0.18}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}\pm {0.20}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}})\times {10}^{-4}$ and $(2.51\pm {0.44}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}\pm {0.11}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}})\times {10}^{-5}$, respectively. The statistical significances of $D^0\to \gamma {\bar{K}}^{\ast 0}$ and $D^0\to \gamma \phi$ 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 $C\text{\hspace{0.17em}⁣}P$ asymmetry ${\mathcal{A}}_{C\text{\hspace{0.17em}⁣}P}(D^0\to \gamma {\bar{K}}^{\ast 0})=(-0.7\pm {5.0}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}\pm {4.1}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}})\mathrm{\%}$ is consistent with $C\text{\hspace{0.17em}⁣}P$ conservation.