Study of Bc+→χcπ+Bc+​→χc​π+ decays

A study of B+c → χcπ+ 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 → χc2π+ 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 BB+c →χc2π+BB+c →J/ψπ+= 0.37 ± 0.06 ± 0.02 ± 0.01 , where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the χc2 → J/ψγ branching fraction. No significant B+c → χc1π+ signal is
observed and an upper limit for the relative branching fraction for the B+c → χc1π+ andB+c → χc2π+ decays of BB+c →χc1π+BB+c →χc2π+< 0.49 is set at the 90% confidence level.