Measurement of the $\Lambda_b^0$ lifetime and mass in the ATLAS experiment

A measurement of the $\Lambda_b^0$ lifetime and mass in the decay channel $\Lambda_b^0\to J/\psi(\mu^+\mu^-) \Lambda^0 (p^+\pi^-)$ is presented here. The analysis uses a signal sample of about 2200 $\Lambda_b^0$ and $\bar\Lambda_b^0$ candidates that are reconstructed in 4.9 fb$^{-1}$ of ATLAS data collected in 2011 at the LHC centre-of-mass energy of 7 TeV. A simultaneous mass and decay time maximum likelihood fit is used to extract the $\Lambda_b^0$ lifetime and mass. They are measured to be $\tau_{\Lambda_b} = 1.449 \pm 0.036({\rm stat}) \pm 0.017({\rm syst})$ ps and $m_{\Lambda_b} = 5619.7 \pm 0.7({\rm stat}) \pm 1.1({\rm syst})$ MeV.