Upper limit on the eta -> pi+pi- branching ratio with the KLOE experiment

TL;DR

This paper reports a search for the rare eta -> pi+pi- decay using the KLOE detector, setting an upper limit on its branching ratio due to the absence of a detected signal.

Contribution

The study provides the first experimental upper limit on the eta -> pi+pi- decay branching ratio using the KLOE detector data.

Findings

No signal for eta -> pi+pi- decay was observed.

An upper limit on the branching ratio was set at 1.3 x 10^-5 at 90% confidence level.

The result constrains models predicting CP violation in eta decays.

Abstract

We have searched with the KLOE detector for the P and CP violating decay eta -> pi^+pi^- in a sample of 1.55 x 10^7 eta's from the decay phi -> eta gamma of phi mesons produced in e+e- annihilations at DAFNE. No signal is found. We obtain the upper limit BR(eta -> pi^+pi^-) < 1.3 x 10^-5 at 90% confidence level.