Precision measurement of the Λb0 baryon lifetime

The ratio of the Λb0 baryon lifetime to that of the B ^̄0 meson is measured using 1.0 fb ^-1 of integrated luminosity in 7 TeV center-of-mass energy pp collisions at the LHC. The Λb0 baryon is observed for the first time in the decay mode Λb0→J/ψpK ^-, while the B ^̄0 meson decay used is the well known B ^̄0→J/ψπ ⁺K ^- mode, where the π ⁺K ^- mass is consistent with that of the K ^̄*0(892) meson. The ratio of lifetimes is measured to be 0.976±0.012±0.006, in agreement with theoretical expectations based on the heavy quark expansion. Using previous determinations of the B ^̄0 meson lifetime, the Λb0 lifetime is found to be 1.482±0.018±0.012 ps. In both cases, the first uncertainty is statistical and the second systematic.