Search for the Decay Kl -> pi0 e+ e-

TL;DR

This paper reports a search for the rare decay Kl -> pi0 e+ e- at Fermilab, aiming to measure its branching ratio to test CP violation and explore potential new physics, but only sets an upper limit due to limited observations.

Contribution

First experimental search for Kl -> pi0 e+ e- decay, providing an upper limit on its branching ratio to constrain CP violation models.

Findings

Observed 2 events with expected background of 1.06

Set an upper limit on branching ratio: < 5.1 x 10^-10

Results support constraints on CP violation theories

Abstract

We report on a search for the decay Kl -> pi0 e+ e- carried out by the KTeV/E799 experiment at Fermilab. This decay is expected to have a significant CP violating contribution and the measurement of its branching ratio could support the CKM mechanism for CP violation or could point to new physics. Two events were observed in the 1997 data with an expected background of 1.06 +-0.41 events, and we set an upper limit Br(Kl -> pi0 e+ e-) < 5.1 x 10^-10 at the 90% confidence level.