Search for the Rare Decays KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-

TL;DR

This study searched for rare KL decay modes involving muon pairs and a potential new neutral boson, setting upper limits that challenge the hypothesis of X0 explaining the HyperCP anomaly.

Contribution

The paper provides the first upper limits on these rare decay modes, constraining the existence of the proposed X0 boson as an explanation for HyperCP results.

Findings

No evidence for the decays was observed.

Upper limits set on branching ratios are below 10^{-10}.

Results exclude X0 as a real pseudoscalar explaining HyperCP.

Abstract

The KTeV E799 experiment has conducted a search for the rare decays KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-, where the X0 is a possible new neutral boson that was reported by the HyperCP experiment with a mass of (214.3 pm 0.5) MeV/c^{2}. We find no evidence for either decay. We obtain upper limits of Br(KL->pi0pi0X0->pi0pi0mu+mu-) < 1.0 x 10^{-10} and Br(KL->pi0pi0mu+mu-) < 9.2 x 10^{-11} at the 90% confidence level. This result rules out the pseudoscalar X0 as an explanation of the HyperCP result under the scenario that the \bar{d}sX0 coupling is completely real.