at the Tevatron

We report Tevatron results on the B c − meson in Run II. The B c − meson has been observed in semileptonic decays, B c − → J / ψ l − ν X , by both the CDF and DO collaborations at a significance greater than 5 σ . For DO, the candidate B c − → J / ψ μ − X events are used to extract measurements of the mass and lifetime of the B c − meson. For CDF, the B c − → J / ψ l − ν X observations have resulted in measurements of the relative production times branching ratio with respect to B − → J / ψ K − decays and a precise determination of the lifetime of the B c − : c τ ( B c − ) = 0.474 −0.066 +0.073 ± 0.033 ps . Also for CDF, an observation of B c − → J / ψ π − decays at a significance exceeding 6 σ results in a precise determination of the mass of the B c − : M ( B c − ) = 6275.2 ± 4.3 ± 2.3 MeV / c 2 .