Observation of the Λ b 0 → χ c 1 $$ {\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}1} $$ (3872) pK− decay

Abstract

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 Λ b 0 → χ c 1 $$ {\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}1} $$ (3872)pK− with χc1(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 χc1(3872)Λ(1520). The branching fraction with respect to that of the Λ b 0 $$ {\Lambda}_{\mathrm{b}}^0 $$ → ψ(2S)pK− decay mode, where the ψ(2S) meson is reconstructed in the J/ψ π+π− final state, is measured to be: β Λ b 0 → χ c 1 3872 pK − β Λ b 0 → ψ 2 S pK − × β χ c 1 3872 → J / ψ π + π − β ψ 2 S → J / ψ π + π − = 5.4 ± 1.1 ± 0.2 × 10 − 2 , $$ \frac{\beta \left({\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}1}(3872){\mathrm{pK}}^{-}\right)}{\beta \left({\Lambda}_{\mathrm{b}}^0\to \uppsi \left(2\mathrm{S}\right){\mathrm{pK}}^{-}\right)}\times \frac{\beta \left({\upchi}_{\mathrm{c}1}(3872)\to \mathrm{J}/\uppsi {\uppi}^{+}{\uppi}^{-}\right)}{\beta \left(\uppsi \left(2\mathrm{S}\right)\to \mathrm{J}/\uppsi {\uppi}^{+}{\uppi}^{-}\right)}=\left(5.4\pm 1.1\pm 0.2\right)\times {10}^{-2}, $$ where the first uncertainty is statistical and the second is systematic.

Keywords

• B physics
• Branching fraction
• Exotics
• Hadron-Hadron scattering (experiments)