Study of the χ$_{c1}$(3872) State in Decays of Beauty Hadrons in the LHCb Experiment

The first observation of the $\Lambda _{b}^{0}$ → χ$_{c1}$(3872)pK$^{–}$ decay and the results of precision measurements of χ$_{c1}$(3872) state parameters in the B$^{+}$ → χ$_{c1}$(3872)K$^{+}$ decays are presented. Relative branching fractions of $\Lambda _{b}^{0}$ → χ$_{c1}$(3872)pK$^{–}$ and $\Lambda _{b}^{0}$ → ψ(2S)pK$^{–}$ decays, as well as B$^{+}$ → χ$_{c1}$(3872)K$^{+}$ and B$^{+}$ → ψ(2S)K$^{+}$ are measured. The χ$_{c1}$(3872) state mass is determined with high accuracy, and the natural particle width is measured for first time. The study is performed using the data collected by the LHCb detector in proton–proton collisions at center-of-mass energies of 7, 8, and 13 TeV.