Measurement of the $B_c^{+}$ Meson Lifetime Using the Decay Mode $B_c^{+}\to J/\psi e^{+}{\nu }_e$

We present a measurement of the $B_c^{+}$ meson lifetime in the decay mode $B_c^{+}\to J/\psi e^{+}{\nu }_e$ using the Collider Detector at Fermilab II detector at the Fermilab Tevatron Collider. From a sample of about $360{\mathrm{pb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$, we reconstruct $J/\psi e^{+}$ pairs with invariant mass in the kinematically allowed range $4<M_{J/\psi e}<6\mathrm{GeV}/{\mathrm{c}}^2$. A fit to the decay-length distribution of 238 signal events yields a measured $B_c^{+}$ meson lifetime of $0.463\genfrac{}{}{0ex}{}{+0.073}{-0.065}(\mathrm{stat})\pm 0.036(\mathrm{syst})\mathrm{ps}$.

Figure 1

$M_{J/\psi e}$ distribution of $J/\psi e^{+}$ pairs (dots with error bars) with $L_{xy}/{\sigma }_{L_{xy}}>3$ together with the expected shape (dashed line) from a sum of a MC signal and the estimated background (solid lines) which is mostly from $b$-hadron decays. The false $J/\psi$ is already removed in the distribution.

Figure 2

Distribution of $K$ for $M_{J/\psi e}$ within (a) 4–4.5, (b) 4.5–5.0, (c) 5.0–5.5, and (d) $5.5–6.0\mathrm{GeV}/{\mathrm{c}}^2$.

Figure 3

$c{t}^{\prime }$ PDF obtained from fits to background samples (points with error bars) for (a) false $J/\psi$ (solid lines), (b) $b\overline{b}$ (solid lines), (c) false electron (hatched area), and (d) conversion electron (hatched area). In (c) and (d), the solid lines are the sum of false $J/\psi$ (shaded area) and a false or conversion electron. The false $J/\psi$ fraction and lifetime shape in (c) and (d) are constrained to that obtained from sideband events.

Figure 4

$c{t}^{\prime }$ distribution from 783 $B_c^{+}$ candidates. The points with error bars are data points and the solid line is the fit result. The dashed line is the $B_c^{+}$ signal and the dotted line is the background.