Study of $B\to X(3872)K$, with $X(3872)\to J/\psi {\pi }^{+}{\pi }^{-}$

We present measurements of the decays $B^{+}\to X(3872)K^{+}$ and $B^0\to X(3872)K^0$ with $X(3872)\to J/\psi {\pi }^{+}{\pi }^{-}$. The data sample used, collected with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ asymmetric-energy storage ring, corresponds to $455\times {10}^{6}B\overline{B}$ pairs. Branching fraction measurements of $\mathcal{B}(B^{+}\to X(3872)K^{+})\times \mathcal{B}(X(3872)\to J/\psi {\pi }^{+}{\pi }^{-})=(8.4\pm 1.5\pm 0.7)\times {10}^{-6}$ and $\mathcal{B}(B^0\to X(3872)K^0)\times \mathcal{B}(X(3872)\to J/\psi {\pi }^{+}{\pi }^{-})=(3.5\pm 1.9\pm 0.4)\times {10}^{-6}$ are obtained. We set an upper limit on the natural width of the $X(3872)$ of $\Gamma <3.3\mathrm{MeV}/c^2$ at the 90% confidence level.

Figure 1

Fits to the $m(J/\psi {\pi }^{+}{\pi }^{-})$ distributions of (top) $B^{+}\to X(3872)K^{+}$ and (bottom) $B^0\to X(3872)K_S^0$ candidates drawn from the $413{\mathrm{fb}}^{-1}$ sample. The dashed line represents the combinatorial background PDF and the solid line the sum of background plus the signal PDF.