Upper limit on the branching ratio for the decayπ0→νν¯

A sample of kinematically identified K{sup +}{yields}{pi}{sup +}{pi}{sup 0} decays obtained with the E949 detector was used to search for the helicity-suppressed decay {pi}{sup 0}{yields}{nu}{nu} resulting in an upper limit of 2.7x10{sup -7} at 90% confidence level. The upper limit is also applicable to {pi}{sup 0} decays into unknown weakly-interacting particles.