Measurement of the Branching Ratio of the KL -> pi+pi- decay with the KLOE Detector

TL;DR

This paper reports a precise measurement of the branching ratio for the CP-violating decay KL->pi+pi- using data from the KLOE detector, providing key parameters for understanding CP violation in kaon decays.

Contribution

The study provides the most accurate measurement of BR(KL->pi+pi-) and related CP violation parameters using a large dataset from the KLOE experiment.

Findings

BR(KL->pi+pi-) = (1.963 ± 0.012 ± 0.017) x 10^-3

|η_{+-}| = (2.219 ± 0.013) x 10^-3

|ε| = (2.216 ± 0.013) x 10^-3

Abstract

We present a measurement of the branching ratio of the CP violating decay KL->pi+pi- performed by the KLOE experiment at the phi factory DAFNE. We use 328 pb-1 of data collected in 2001 and 2002, corresponding to ~ 150 million tagged KL mesons. We find BR(KL->pi+pi-) = $(1.963 +/- 0.012 +/- 0.017)x 10^-3. This branching ratio measurement is fully inclusive of final-state radiation. Using the above result, we determine the modulus of the amplitude ratio |\eta_{+-}| to be (2.219 +/- 0.013)x 10^{-3} and |\epsilon| to be (2.216 +/- 0.013)x 10^{-3}.