Precision measurement of the Lambda_b baryon lifetime

Understand

The ratio of the \Lambda b baryon lifetime to that of the B0 meson is measured using 1.0/fb of integrated luminosity in 7 TeV center-of-mass energy pp collisions at the LHC.

• The \Lambda b baryon is observed for the first time in the decay mode \Lambda b -> J/\psi pK-, while the B0 meson decay used is the well known B0 -> 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 0.976 +/- 0.012 +/- 0.006, in agreement with theoretical expectations based on the heavy quark expansion.
• Using previous determinations of the B0 meson lifetime, the \Lambda b lifetime is found to be 1.482 +/- 0.018 +/- 0.012 ps.