Properties of the $B_c$ Meson

Using more than 250~pb$^{-1}$ of data collected with the D\O\ detector in Run II of the Tevatron, we study the $B_c^+$ meson in the $J/\psi \mu^+ \nu$ and $J/\psi \pi^+$ final states. We use these events to measure the mass and the lifetime of the $B_c$.