Search for the decay $B^0\to J/\psi \gamma$

We present the results of a search for the radiative decay $B^0\to J/\psi \gamma$ in a data set containing $123.0\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays, collected by the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ storage ring at SLAC. We find no evidence for a signal and place an upper limit of $\mathcal{B}(B^0\to J/\psi \gamma )<1.6\times {10}^{-6}$ at 90% confidence level.

Figure 1

Feynman diagram of the leading-order contribution to $B^0\to J/\psi \gamma$.

Figure 2

$\Delta E\mathrm{\text{−}}{m}_{\mathrm{E}\mathrm{S}}$ distributions in the analysis window for (a) on-peak data, (b) simulated signal, and (c) simulated background. The signal region is indicated by a box. The sample in (c) is the original background sample used to optimize the selection; the equivalent luminosity of this sample is about 9 times that of the $113{\mathrm{f}\mathrm{b}}^{-1}$ sample in (a).