A study of the two-body decays $B^{\pm }\to X_{c\overline{c}}{K}^{\pm }$, where $X_{c\overline{c}}$ refers to one charmonium state, is reported by the BABAR Collaboration using a data sample of $424{\mathrm{fb}}^{-1}$. The absolute determination of branching fractions for these decays are significantly improved compared to previous BABAR measurements. Evidence is found for the decay $B^{+}\to X(3872)K^{+}$ at the $3\sigma$ level. The absolute branching fraction $\mathcal{B}[B^{+}\to X(3872)K^{+}]=[2.1\pm 0.6(\text{stat})\pm 0.3(\text{syst})]\times {10}^{-4}$ is measured for the first time. It follows that $\mathcal{B}[X(3872)\to J/\psi {\pi }^{+}{\pi }^{-}]=(4.1\pm 1.3)\%$, supporting the hypothesis of a molecular component for this resonance.

• Received 29 November 2019
• Revised 22 January 2020
• Accepted 20 March 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.152001

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Published by the American Physical Society