Observation of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>B</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>Meson in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">p</mml:mi><mml:mrow><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="italic">p</mml:mi></mml:mrow><mml:mrow><mml:mi>¯</mml:mi></mml:mrow></mml:mover></mml:mrow></mml:mrow></mml:math>Collisions at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>√</mml:mi><mml:mi mathvariant="italic">s</mml:mi><mml:mspace/><mml:mo>=</mml:mo><mml:mspace/><mml:mn>1.8</mml:mn><mml:mn/></mml:math>TeV

We have observed bottom-charm mesons via the decay mode ${B}_{c}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\ell}}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\nu}$ in 1.8 TeV $p\overline{p}$ collisions using the CDF detector at the Fermilab Tevatron. A fit of background and signal contributions to the $J/\ensuremath{\psi}\ensuremath{\ell}$ mass distribution yielded ${20.4}_{\ensuremath{-}5.5}^{+6.2}$ events from ${B}_{c}$ mesons. A fit to the same distribution with background alone was rejected at the level of 4.8 standard deviations. We measured the ${B}_{c}^{+}$ mass to be $6.40\ifmmode\pm\else\textpm\fi{}0.39(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.13(\mathrm{syst})\mathrm{GeV}{/c}^{2}$ and the ${B}_{c}^{+}$ lifetime to be ${0.46}_{\ensuremath{-}0.16}^{+0.18}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.03(\mathrm{syst})\mathrm{ps}$. Our measured yield (production cross section times branching ratio) for ${B}_{c}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\ell}}^{+}\ensuremath{\nu}$ relative to that for ${B}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{+}$ is ${0.132}_{\ensuremath{-}0.037}^{+0.041}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.031(\mathrm{syst}{)}_{\ensuremath{-}0.020}^{+0.032}(\mathrm{lifetime})$.