Measurement of the CP-Violating Phase φs in anti-B0s → J/ψ π+ π− Decays

Measurement of the mixing-induced CP-violating phase φs in anti-B0s decays is of prime importance in probing new physics. Here 7421 ± 105 signal events from the dominantly CP-odd final state J/ψ π+ π- are selected in 1 fb^−1 of pp collision data collected at √s = 7 TeV with the LHCb detector. A time-dependent fit to the data yields a value of φs = (-0.019) -0.174 -0.003 +0.173 +0.004 rad, consistent with the Standard Model expectation. No evidence of direct CP violation is found.