Search for $B^{+}\to X(3872)K^{+}$, $X(3872)\to J/\psi \gamma$

In a study of $B^{+}\to J/\psi \gamma K^{+}$ decays, we find evidence for the radiative decay $X(3872)\to J/\psi \gamma$ with a statistical significance of $3.4\sigma$. We measure the product of branching fractions $\mathcal{B}(B^{+}\to X(3872)K^{+})·\mathcal{B}(X(3872)\to J/\psi \gamma )=(3.3\pm 1.0\pm 0.3)\times {10}^{-6}$, where the uncertainties are statistical and systematic, respectively. We also measure the branching fraction $\mathcal{B}(B^{+}\to {\chi }_{c1}{K}^{+})=(4.9\pm 0.2\pm 0.4)\times {10}^{-4}$. These results are obtained from $(287\pm 3)$ million $B\overline{B}$ decays collected at the ${\rm Y}(4S)$ resonance with the BABAR detector at the PEP-II $B$ Factory at SLAC.

Figure 1

Number of extracted signal events versus $m_{c\overline{c}}$ for ${\chi }_{cJ}$. The solid curve is the fit to the data. The ${\chi }^2$ per degree of freedom for this fit is $48.7/34$.

Figure 2

Number of extracted signal events versus $m_{c\overline{c}}$ for the $X(3872)$ region. The solid curve is the fit to the data. The ${\chi }^2$ per degree of freedom for this fit is $46.3/36$.