Measurement of the CP-violating phase phi(s) in (B)over-bar(s)(0) -> J / psi pi(+)pi(-) decays

The mixing-induced CP-violating phase φs in B0 s and B0 s decays is measured using the J/ψ π+π − final state in data, taken from 3 fb−1 of integrated luminosity, collected with the LHCb detector in 7 and 8 TeV centre-of-mass pp collisions at the LHC. A time-dependent flavour-tagged amplitude analysis, allowing for direct CP violation, yields a value for the phase φs = 70 ± 68 ± 8 mrad. This result is consistent with the Standard Model expectation and previous measurements