Study of charmonium decays to K⁰_SKπ in the B → (K⁰_SKπ)K channels

A study of the B⁺ → K⁰_SK⁺K⁻π⁺ and B⁺ → K⁰_SK⁺K⁺π⁻ decays is performed using proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV at the LHCb experiment. The K⁰_SKπ invariant mass spectra from both decay modes reveal a rich content of charmonium resonances. New precise measurements of the η_c and η_c(2S) resonance parameters are performed and branching fraction measurements are obtained for B⁺ decays to η_c, J/ψ, η_c(2S) and χ_c1 resonances. In particular, the first observation and branching fraction measurement of B⁺ → χ_c0K⁰π⁺ is reported as well as first measurements of the B⁺ → K⁰K⁺K⁻π⁺ and B⁺ → K⁰K⁺K⁺π⁻ branching fractions. Dalitz plot analyses of η_c → K⁰_SKπ and η_c(2S) → K⁰_SKπ decays are performed. A new measurement of the amplitude and phase of the Kπ S-wave as functions of the Kπ mass is performed, together with measurements of the K^∗₀₍1430), K^∗₀(1950) and a₀(1700) parameters. Finally, the branching fractions of χ_c1 decays to K^∗ resonances are also measured.