Measurement of $b$ Hadron Lifetimes in Exclusive Decays Containing a $J/\psi$ in $p\overline{p}$ Collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We report on a measurement of $b$-hadron lifetimes in the fully reconstructed decay modes $B^{+}\to J/\psi K^{+}$, $B^0\to J/\psi K^{*}(892{)}^0$, $B^0\to J/\psi K_s^0$, and ${\Lambda }_b^0\to J/\psi {\Lambda }^0$ using data corresponding to an integrated luminosity of $4.3{\mathrm{fb}}^{-1}$, collected by the CDF II detector at the Fermilab Tevatron. The measured lifetimes are $\tau (B^{+})=[1.639\pm 0.009(\mathrm{stat})\pm 0.009(\mathrm{syst})]\mathrm{ps}$, $\tau (B^0)=[1.507\pm 0.010(\mathrm{stat})\pm 0.008(\mathrm{syst})]\mathrm{ps}$, and $\tau ({\Lambda }_b^0)=[1.537\pm 0.045(\mathrm{stat})\pm 0.014(\mathrm{syst})]\mathrm{ps}$. The lifetime ratios are $\tau (B^{+})/\tau (B^0)=[1.088\pm 0.009(\mathrm{stat})\pm 0.004(\mathrm{syst})]$ and $\tau ({\Lambda }_b^0)/\tau (B^0)=[1.020\pm 0.030(\mathrm{stat})\pm 0.008(\mathrm{syst})]$. These are the most precise determinations of these quantities from a single experiment.

Figure 1

Invariant mass together with mass fit projection for (a) $B^{+}\to J/\psi K^{+}$, (b) $B^0\to J/\psi K^{*}$, and (c) ${\Lambda }_b^0\to J/\psi {\Lambda }^0$.

Figure 2

Decay time distributions for (a) $B^{+}\to J/\psi K^{+}$, (b) $B^0\to J/\psi K^{*}$, and (c) ${\Lambda }_b^0\to J/\psi {\Lambda }^0$ candidates.