New limit on the $K^0_L \to \pi^0 \nu \bar{\nu}$ decay rate

Abstract

The first dedicated experiment for the rare kaon decay $K^0_L \to \pi^0 \nu \bar{\nu}$ has been performed by the E391a collaboration at the KEK 12-GeV proton synchrotron. A new upper limit of $2.1 \times 10^{-7}$ at the 90% confidence level was set for the branching ratio of the decay $K^0_L \to \pi^0 \nu \bar{\nu}$ using about 10% of the data collected during the first period of data taking.