Precision measurement of the $\Lambda_{b}^0$ baryon lifetime

The ratio of the $\Lambda_{b}^0$ baryon lifetime to that of the $\bar{B}^{0}$ meson is measured using data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected with the LHCb detector using $pp$ collisions at the LHC. The $\Lambda_{b}^0$ baryon is observed in the decay mode $\Lambda_{b}^0 \rightarrow J/\psi p K^{-}$, while the $\bar{B}^{0}$ meson decay used is the well known $\bar{B}^{0} \rightarrow J/\psi \pi^{+} K^{-}$ mode, where the $\pi^{+}K^{-}$ mass is consistent with that of the $K^{*0}(892)$ meson. The ratio of lifetimes is measured to be $0.971\pm0.007\pm0.005$, in agreement with theoretical expectations based on the heavy quark expansion. Using previous determinations of the $\bar{B}^{0}$ meson lifetime, the $\Lambda_{b}^0$ lifetime is found to be $1.476 \pm 0.010 \pm 0.010$ ps. In both cases the first uncertainty is statistical and the second systematic.