Charm background must be 1 prong decay and charm production with no other hadrons. Then the backgrounds decrease to 0.1 . And electron from electron pair creation from 2ry hadronic interactions will be backgrounds, at this time this was not included in Monte Calro but these electron momentum should be small. Electron channel is the best channel for detection of tau. This is a exclusion plot.
Solid line shows electron channel limit, electron and hadron channel limit.