Measurement of the Lambda_b lifetime and mass in the ATLAS experiment

TL;DR

This paper reports precise measurements of the Lambda_b baryon's lifetime and mass using ATLAS data, employing a maximum likelihood fit to analyze about 2200 decay events at 7 TeV collision energy.

Contribution

The study provides the first simultaneous measurement of Lambda_b lifetime and mass in the ATLAS experiment with high precision using a large data sample.

Findings

Lambda_b lifetime measured as 1.449 ps with uncertainties

Lambda_b mass measured as 5619.7 MeV with uncertainties

Results are consistent with previous measurements and theoretical predictions

Abstract

A measurement of the Lambda_b lifetime and mass in the decay channel Lambda_b -> J/psi(mu^+ mu^-) Lambda^0(p pi^-) is presented. The analysis uses a signal sample of about 2200 Lambda_b and anti-Lambda_b decays that are reconstructed in 4.9 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 lifetime and mass. They are measured to be tau(Lambda_b) = 1.449 +/- 0.036(stat) +/- 0.017(syst) ps and m(Lambda_b) = 5619.7 +/- 0.7(stat) +/- 1.1(syst) MeV.