Observation of $e^{+} e^{-} to gamma X(3872)$ at BESIII

With data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.009 to 4.420 GeV, the process $e^{+} e^{-} to gamma X(3872)$ is observed for the first time with a statistical significance of $6.3sigma$. The measured mass of the $X(3872)$ is ($3871.9pm 0.7_{rm stat.}pm 0.2_{rm sys.}$) MeV/$c^2$, in agreement with previous measurements. Measurements of the product of the cross section $sigma[e^{+} e^{-} to gamma X(3872)]$ and the branching fraction $mathcal{B}[X(3872) to pi^{+} pi^{-} J/psi]$ at center-of-mass energies 4.009, 4.229, 4.260, and 4.360 GeV are reported. Our measurements are consistent with expectations for the radiative transition process $Y(4260) to gamma X(3872)$.