Search for the decay K_L-> pi^0 nu nubar

TL;DR

This paper reports a search for the rare decay K_L -> pi^0 nu nubar using Fermilab's KTeV experiment, setting an upper limit on its branching ratio due to the observation of one candidate event.

Contribution

First search for K_L -> pi^0 nu nubar in the KTeV experiment, establishing an upper limit on its branching ratio at 90% confidence level.

Findings

Observed one candidate event consistent with background

Set an upper limit on the branching ratio at 1.6 x 10^-6

Demonstrated the feasibility of searching for this rare decay

Abstract

We report on a search for the rare decay K_L -> pi^0 nu nubar in the KTeV experiment at Fermilab. We searched for two-photon events whose kinematics were consistent with an isolated pi^0 coming from the decay K_L -> pi^0 nu nubar. One candidate event was observed, which was consistent with the expected level of background. An upper limit on the branching ratio was determined to be B(K_L -> pi^0 nu nubar) < 1.6E-6 at the 90% confidence level.