Measurement of the CP-violating phase φs in (B)over-bars0 → J/ψπ+π- decays

Measurement of the mixing-induced CP-violating phase phi(s) in (B) over bar (0)(s) decays is of prime importance in probing new physics. Here 7421 +/- 105 signal events from the dominantly CP-odd final state J/psi pi(+)pi(-) are selected in 1 fb(-1) of pp collision data collected at root s = 7 TeV with the LHCb detector. A time-dependent fit to the data yields a value of phi(s) = -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. (C) 2012 Elsevier B.V. All rights reserved.