English: Distribution of the particle identification (PID) parameter used to classify Cherenkov rings as electron-like and muon-like. Events to the left of the blue line are classified as electron-like and those to the right as muon-like. The filled histograms show the expected number of single ring events after neutrino oscillations. The PID algorithm uses properties of the light distribution such as the blurriness of the Cherenkov ring to classify events. The insets show examples of an electron-like (left) and muon-like (right) Cherenkov ring.