Charged particle fluctuations and microscopic models of nuclear collisions

We study the event-by-event fluctuations of the charged particles and compare the results of different Monte Carlo generators (MCG): VNIb, HIJING, HIJING/BB̄, and RQMD. We find that the D-measure can be used to distinguish between the different gluon populations that are present in the MCG models. On the other hand, the value of the D-measure shows high sensitivity to the rescattering effects in VNIb model, but lower sensitivity to the rescattering effects in RQMD model. We also find that the D-measures from AA are consistent with the D-measures from pp for all generators except VNIb. Therefore, any deviation among the values of D-measure for different impact parameters and between pp and AA collisions may indicate that either the rescattering effects play a key role in the interactions or there is new physics in AA collisions.