A fully reconstructed Bc --> Jpsi Pi signal is observed with the D0 detector at the Fermilab Tevatron p-pbar collider. Using 1.3 inverse femtobarns of integrated luminosity, the signal is extracted with a significance more than five standard deviations above background. The measured Bc meson mass is 6300 (+-) 14 (stat) (+-) 5 (sys) MeV/cc
Tanasijczuk, A. J., D0, & et al. (2008). Observation of the $B_c$ Meson in the Exclusive Decay $B_c \to J/\psi \pi$. Physical Review Letters, 101. https://doi.org/10.1103/PhysRevLett.101.012001 (Original work published 2008)