Measurement of the flavour-specific CP violating asymmetry asl in B0s decay

The CP violating asymmetry asl is studied with a sample of Bs0 or Bs0bar semi-muonic decays in proton-proton collisions at a centre-of-mass energy of 7 TeV at LHCb with an integrated luminosity of 1 fb^-1. The final state studied is Ds{\mu}, with Ds reconstructed in the final state {\phi}{\pi}. The Ds{\mu} yields are summed over untagged Bs0 and Bs0bar initial states, and integrated with respect to decay time. Data driven methods have been developed to measure all the efficiency ratios needed to determine asl from the measured raw asymmetry. We obtain asl= (-0.24+/-0.54+/-0.33)%, where the first uncertainty is statistical and the second systematic.