Evaluating the charged background rejection requirement in an experiment   to measure $\rm BR(K_L \to \pi^0 \nu \bar{\nu})$ at the CERN SPS
  Measuring the rate at which the long-lived, neutral kaon decays into a neutral pion, neutrino, and anti-neutrino allows physicists an opportunity to test precise predictions made by the Standard Model. Differences between theoretical predictions and experimental measurements may point to new physics. Not only does the Standard Model predict a very low probability at approximately 3 $K_L \to \pi^0 \nu \bar{\nu}$ decays in 100 billion $K_L$ decays, but many of the common decays leave false signals in the detector that look the same as the true signal. Charged decays have been studied to determine the required detection efficiency necessary to eliminate them. The conclusion of these studies is that a reduction by a factor of $1/(3\times10^9)$ will be required to achieve the 10:1 signal to charged background ratio necessary for the experiment. 
Austin Bradley
hep-ex physics.ins-det