Measurement of the flavour-specific CP-violating asymmetry <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msubsup><mml:mrow><mml:mi>a</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">sl</mml:mi></mml:mrow><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msubsup></mml:math> in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"><mml:msubsup><mml:mrow><mml:mi>B</mml:mi></mml:mrow><mml:mrow><mml:mi>s</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msubsup></mml:math> decays

The CP-violating asymmetry as&#13;\nsl is studied using semileptonic decays of B0s&#13;\nand B0s&#13;\nmesons produced in&#13;\npp collisions at a centre-of-mass energy of 7 TeV at the LHC, exploiting a data sample corresponding&#13;\nto an integrated luminosity of 1.0 fb−1. The reconstructed final states are D±&#13;\ns μ∓, with the D±&#13;\ns particle&#13;\ndecaying in the φπ± mode. The D±&#13;\ns μ∓ yields are summed over B0s&#13;\nand B0s&#13;\ninitial states, and integrated&#13;\nwith respect to decay time. Data-driven methods are used to measure efficiency ratios. We obtain as&#13;\nsl&#13;\n=&#13;\n(−0.06±0.50±0.36)%, where the first uncertainty is statistical and the second systematic.