EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN) CERN-PH-EP-2013-141

The CP-violating asymmetry assl is studied using semileptonic decays of B0s and B 0 s 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−1. The reconstructed final states are D±s µ∓, with the D±s particle decaying in the φpi ± mode. The D±s µ ∓ yields are summed over B0s and B0s initial states, and integrated with respect to decay time. Data-driven methods are used to measure efficiency ratios. We obtain assl = (−0.06 ± 0.50 ± 0.36)%, where the first uncertainty is statistical and the second systematic. †Authors are listed on the following pages. ar X i