## Observation of the Λ0b →χc1 (3872) pK- decay

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Original language English 28 Journal of High Energy Physics 2019 https://doi.org/10.1007/JHEP09(2019)028 Published - 3 Sep 2019

### Abstract

Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9 fb$^{−1}$ of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay ${\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}1}$ (3872)pK$^{−}$ with χ$_{c1}$(3872) → J/ψ π$^{+}$π$^{−}$ is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that (58 ± 15)% of the decays proceed via the two-body intermediate state χ$_{c1}$(3872)Λ(1520). The branching fraction with respect to that of the ${\Lambda}_{\mathrm{b}}^0$ → ψ(2S)pK$^{−}$ decay mode, where the ψ(2S) meson is reconstructed in the J/ψ π$^{+}$π$^{−}$ final state, is measured to be: $\frac{\beta \left({\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}1}(3872){\mathrm{pK}}^{-}\right)}{\beta \left({\Lambda}_{\mathrm{b}}^0\to \uppsi \left(2\mathrm{S}\right){\mathrm{pK}}^{-}\right)}\times \frac{\beta \left({\upchi}_{\mathrm{c}1}(3872)\to \mathrm{J}/\uppsi {\uppi}^{+}{\uppi}^{-}\right)}{\beta \left(\uppsi \left(2\mathrm{S}\right)\to \mathrm{J}/\uppsi {\uppi}^{+}{\uppi}^{-}\right)}=\left(5.4\pm 1.1\pm 0.2\right)\times {10}^{-2},$

ID: 155214290