Measurement of the ratio Γ(KL → π+π-)/Γ(KL → π±e∓ν) and extraction of the CP violation parameter |η+-|

We present a measurement of the ratio of the decay rates Gamma(K-L -> pi(+)pi(-))/Gamma(K-L -> pi +/- e -/+nu), denoted as Gamma(K2 pi)/Gamma(Ke3). The analysis is based on data taken during a dedicated run in 1999 by the NA48 experiment at the CERN SPS. Using a sample of 47 000 K-2 pi and five million K-e3 decays, we find Gamma(K2 pi)/Gamma(Ke3) = (4.835 +/- 0.022stat. +/- 0.016syst.) x 10(-3). From this we derive the branching ratio of the CP violating decay K-L -> pi(+)pi(-) and the CP violation parameter vertical bar eta+-vertical bar. Excluding the CP conserving direct photon emission component K-L -> pi(+)pi(-)gamma, we obtain the results BR(K-L -> pi(+)pi(-)) = (1.941 +/- 0.019) x 10(-3) and vertical bar eta+-vertical bar = (2.223 +/- 0.012) x 10(-3). (c) 2006 Elsevier B.V. All rights reserved.