Search for the decay

Data collected in Fermilab experiment E731 was used to perform the first search for the decay K L → π 0 vv. This decay is dominated by short distance effects and is almost entirely direct CP violating within the standard model. Cuts were developed to reject the background processes Λ → nπ 0 and K L → π + e − γv. No candidate events were seen. We find BR (K L → π 0 vv) < 2.2.×10 − at the 90% confidence level