Observation of the ${\Lambda }_b^0\to {\chi }_{c1}(3872)p{K}^{-}$ decay

Abstract

Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9fb${}^{-1}$ of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay ${\Lambda }_b^0\to {\chi }_{c1}(3872)p{K}^{-}$ with ${\chi }_{c1}\to J/\psi {\pi }^{+}{\pi }^{-}$ is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that $(58\pm 15)\%$ of the decays proceed via the two-body intermediate state ${\chi }_{c1}(3872)\Lambda (1520)$. The~branching fraction with respect to that of the ${\Lambda }_b\to \psi (2S)p{K}^{-}$ decay mode, where the $\psi (2S)$~meson is reconstructed in the $J/\psi {\pi }^{+}{\pi }^{-}$ final state, is measured to be: \begin{equation*} \frac{Λ_b^0\toχ_{c1}(3872)pK^-}{Λ_b\toψ(2S)p K^-} \times \frac{\mathcal{B}(χ_{c1} \to J/ψπ^+π^-)}{\mathcal{B}(ψ(2S)\to J/ψπ^+π^-)} = \left(5.4 \pm 1.1 \pm 0.2\right)\times 10^{-2}\,, \end{equation*} where the first uncertainty is statistical and the second is systematic.

arXiv comment19 pages, 2 figures. All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2019-023.html

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