Analytical calculation of dEdx cluster-charge loss due to threshold effects

This letter presents a simple analytical approximation which allows one to estimate the effect of ADC threshold on the measured cluster-charge size as used for dEdx determinations. The idea is to gain some intuitive understanding of the cluster-charge loss and not to replace more accurate simulations. The method is applied to the multiple sampling measurements of energy loss in the Main Time Projection Chambers (TPCs) of the NA49 experiment at CERN SPS. The calculations are in reasonable agreement with data.