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/c², using the B⁺ _c → J/ψpp¯π⁺ channel.