A new limit on the CP violating decay KS -> 3pi0 with the KLOE experiment

TL;DR

This paper reports a new experimental upper limit on the rare CP-violating decay KS -> 3pi0, achieved through improved detection and background rejection techniques at the KLOE experiment, significantly tightening previous constraints.

Contribution

The study provides the most stringent upper limit to date on the branching ratio of KS -> 3pi0 decay, enhancing the sensitivity of CP violation searches in kaon decays.

Findings

No candidate events observed in data.

Upper limit on BR(KS -> 3pi0) set at 2.6 x 10^-8.

Improved the limit on eta_000 parameter to 0.0088.

Abstract

We have carried out a new direct search for the CP violating decay KS -> 3pi0 with 1.7 fb^-1 of e+e- collisions collected by the KLOE detector at the phi-factory DAFNE. We have searched for this decay in a sample of about 5.9 x 10^8 KS KL events tagging the KS by means of the KL interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake KS tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of KS -> 2pi0 events in the same sample, we set the upper limit on BR(KS -> 3pi0 < 2.6 x 10^-8 at 90% C.L., five times lower than the previous limit. We also set the upper limit on the eta_000 parameter, |eta_000 | < 0.0088 at 90% C.L., improving by a factor two the latest direct measurement.