First observation of a baryonic B⁺c decay

A baryonic decay of the B ⁺ _c meson, B ⁺ _c → J/ψpp¯π ⁺, is observed for the first time, with a significance of 7.3 standard deviations, in pp collision data collected with the LHCb detector and corresponding to an integrated luminosity of 3.0 fb _-1 taken at center-of-mass energies of 7 and 8 TeV. With the B ⁺ _c → J/ψπ ⁺ decay as the normalization channel, the ratio of branching fractions is measured to be B(B ⁺ _c → J/ψpp¯π ⁺)/B(B ⁺ _c → J/ψπ ⁺) = 0.143 ^+0.039 _-0.034(stat) ± 0.013(syst). The mass of the B ⁺ _c meson is determined as M(B ⁺ _c) = 6274.0 ± 1.8(stat) ± 0.4(syst) MeV/c ², using the B ⁺ _c → J/ψpp¯π ⁺ channel.