CP Violation at ATLAS

The Standard Model predicts a tiny CP-violating effects in the Bs-meson system that can be experimentally determined by the ATLAS experiment at LHC, employing a time-dependent analysis of the ‘golden’ BsJpsiphi decay channel to extract the weak mixing phase phi_s. Precise measurement of the mass and lifetime of the B-hadron is crucial for the measurement of the CP-violating quantities. To validate this we test the performance of the ATLAS detector by measuring the mass and lifetime of the B_s meson using the BsJPsiphi decay. In parallel, the measurement of the mass and lifetime of the B_d meson is performed, using the decay channel BdJpsiK*0, as it represents an excellent control channel. The final state particles from BsJpsiphi and BdJPsiK*0 decays are reconstructed in the ATLAS detector using proton-proton collision data at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 40 pb-1. Within the statistical uncertainties the fitted masses and lifetimes of both B mesons are consistent with the world average values.