Study of Bc+→χcπ+ decays

A study of B_c⁺→χ_cπ⁺ decays is reported using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb⁻¹. The decay B_c⁺→χ_c2π⁺ is observed for the first time, with a significance exceeding seven standard deviations. The relative branching fraction with respect to the B_c⁺→J/ψπ⁺ decay is measured to be (Formula presented.) where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the χ_c2→ J/ψγ branching fraction. No significant B_c⁺→χ_c1π⁺ signal is observed and an upper limit for the relative branching fraction for the B_c⁺→χ_c1π⁺ and B_c⁺→χ_c2π⁺ decays of (Formula presented.) is set at the 90% confidence level.