Measurement of the CP-violating phase Φs in B⁰s → J/ψπ⁺π^- decays

Measurement of the mixing-induced CP-violating phase Φ _s in B ⁰ _s decays is of prime importance in probing new physics. Here 7421 ± 105 signal events from the dominantly CP-odd final state J/ψπ ⁺π ^- are selected in 1 fb ^-1 of pp collision data collected at √ s = 7 TeV with the LHCb detector. A timedependent fit to the data yields a value of Φ _s = -0.019 ^+0.173+0.004 _-0.174-0.003 rad, consistent with the Standard Model expectation. No evidence of direct CP violation is found.