This presentation reports on the first experimental search for the decay Klong to $\pi^0 \pi^0 \mu^+ \mu^-$ based on data collected by the KTeV experiment. Although this decay mode is possible within the standard model, its rate is phase space suppressed. The HyperCP experiment has recently observed 3 $\Sigma^+ \to p \mu^+ \mu^-$ events within a narrow di-muon mass range, suggesting that the process may occur via a new neutral state: $\Sigma^+ \to p X^0, X^0 \to\mu^+ \mu^-$ with $m(X^0) = 214.3\mev$. The $X^0$ would create an $s$- to $d$- quark transition at a rate that would cause Klong to $\pi^0 \pi^0 X, ^0 \to\mu^+ \mu^-$ to occur at rates considerably over the standard model expectation. Our preliminary results significantly constrain this possibility.
Categories: hep-ex