Measurement of the $B_c^{\mathbf{-}}$ meson lifetime in the decay $B_c^{\mathbf{-}}\to J/\psi {\pi }^{\mathbf{-}}$

The lifetime of the $B_c^{-}$ meson is measured using 272 exclusive $B_c^{-}\to J/\psi (\to {\mu }^{+}{\mu }^{-}){\pi }^{-}$ decays reconstructed in data from proton-antiproton collisions corresponding to an integrated luminosity of $6.7{\mathrm{fb}}^{-1}$ recorded by the CDF II detector at the Fermilab Tevatron. The lifetime of the $B_c^{-}$ meson is measured to be $\tau (B_c^{-})=0.452\pm 0.048(\mathrm{stat})\pm 0.027(\mathrm{syst})\mathrm{ps}$. This is the first measurement of the $B_c^{-}$ meson lifetime in a fully reconstructed hadronic channel, and it agrees with previous results and has comparable precision.

Figure 1

Invariant-mass distribution of $J/\psi K^{-}$ candidates. The hatched areas are the sideband regions, and the signal region lies between them.

Figure 2

Invariant-mass distribution of $J/\psi {\pi }^{-}$ candidates. The hatched areas are the sideband regions, and the signal region lies between them. The fit result is overlaid in the signal region, as well as the signal and background components.

Figure 3

The ${\sigma }_{ct}$ distribution of $J/\psi K^{-}$ candidates obtained from the simulation is compared with data.

Figure 4

Comparison of efficiency for $B^{-}\to J/\psi K^{-}$ obtained from data and the fit result from simulation. Also shown is the fit result for $B_c^{-}\to J/\psi {\pi }^{-}$ simulation.

Figure 5

Decay-length distribution of $J/\psi {\pi }^{-}$ candidates. The fit projection, along individual contributions from signal and background, is overlaid.