Measurement of the flavour-specific CP -violating asymmetry asls in Bs0 decays

The CP  -violating asymmetry asls is studied using semileptonic decays of Bs0 and B¯s0 mesons produced in pp   collisions at a centre-of-mass energy of 7 TeV at the LHC, exploiting a data sample corresponding to an integrated luminosity of 1.0 fb−11.0 fb−1. The reconstructed final states are Ds±μ∓, with the Ds± particle decaying in the ϕπ±ϕπ± mode. The Ds±μ∓ yields are summed over B¯s0 and Bs0 initial states, and integrated with respect to decay time. Data-driven methods are used to measure efficiency ratios. We obtain asls=(−0.06±0.50±0.36)%, where the first uncertainty is statistical and the second systematic.