Upper Limit on the Branching Ratio for the Decay ${\pi }^0\to \nu \bar{\nu }$

Abstract

A sample of kinematically identified $K^{+}\to {\pi }^{+}{\pi }^0$ decays obtained with the E949 detector was used to search for the helicity-suppressed decay ${\pi }^0\to \nu \bar{\nu }$ resulting in an upper limit of $2.7\times 10^{-7}$ at 90% confidence level.The upper limit is also applicable to ${\pi }^0$ decays into unknown weakly interacting particles.

9 pages, 3 figures; no change in the results, accepted for publication in Physical Review D