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. The analysis uses a signal sample of about 2200 ${\Lambda }_b^0$ and ${\overline{\Lambda }}_b^0$ decays that are reconstructed in $4.9{\mathrm{fb}}^{-1}$ of ATLAS $pp$ collision data collected in 2011 at the LHC center-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 ${\tau }_{{\Lambda }_b}=1.449\pm 0.036(\mathrm{stat})\pm 0.017(\mathrm{syst})\mathrm{ps}$ and $m_{{\Lambda }_b}=5619.7\pm 0.7(\mathrm{stat})\pm 1.1(\mathrm{syst})\mathrm{MeV}$.

• Received 10 July 2012

DOI:https://doi.org/10.1103/PhysRevD.87.032002

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© 2013 CERN, for the ATLAS Collaboration