Abstract
We present a measurement of the ratio of the decay rates Gamma(KL -> pi+ pi-)/Gamma(KL -> pi e nu), denoted as Gamma(K2pi)/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 47000 K2pi and five million Ke3 decays, we find Gamma(K2pi)/Gamma(Ke3) = (4.835 +- 0.022(stat) +- 0.016(syst)) x 10^-3. From this we derive the branching ratio of the CP violating decay KL -> pi+ pi- and the CP violation parameter |eta+-|. Excluding the CP conserving direct photon emission component KL -> pi+ pi- gamma, we obtain the results BR(KL -> pi+ pi-) = (1.941 +- 0.019) x 10^-3 and |eta+-| = (2.223 +- 0.012) x 10^-3.
Highlights
In the last two years, the present generation of high-statistics kaon experiments (KTeV, KLOE and NA48) have published various measurements of the main KL decay modes, several of them being in disagreement with the PDG averages given in [1]
In [3], we reported on the measurement of the ratio of Ke3 to all KL decays with two charged tracks, leading to a branching ratio BR(Ke3) which exceeds the PDG value by (3.3 ± 1.3)%, or 2.5 standard deviations
Following a thin Kevlar window, a tank filled with helium near atmospheric pressure contained the magnetic spectrometer to measure the momenta of the charged particles. It consisted of four drift chambers (DCH), each with 8 planes of sense wires oriented along four directions, each one rotated by 45 degrees with respect to the previous one
Summary
In the last two years, the present generation of high-statistics kaon experiments (KTeV, KLOE and NA48) have published various measurements of the main KL decay modes, several of them being in disagreement with the PDG averages given in [1]. In [2], results for the six largest KL branching fractions were presented, determined by measuring ratios of decay rates, where the charged decay modes were normalized to Ke3. The measurement of the ratio ΓK2π /ΓKe3 disagrees with the PDG by 10%, and the results for BR(KL → π +π −) and |η+−| disagree with the PDG by 5%, or more than four standard deviations, respectively. In [3], we reported on the measurement of the ratio of Ke3 to all KL decays with two charged tracks, leading to a branching ratio BR(Ke3) which exceeds the PDG value by (3.3 ± 1.3)%, or 2.5 standard deviations. We used the same data sample and applied similar cuts to select events with two tracks and Ke3 decays
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