Pion shower rejection as a function of number of used eigen-vectors.
Electron and hadron has difference not only in shower shape but also in shower fluctuation. This difference was used to identify electrons and pions. If number of used eigen-vector is increased, the score improves. However small amplitude vectors are noisy and including them does not improve the score any more. In 4GeV case, including more than 7~8 vectors are not so much effective.
