Poisson baseline of net-charge fluctuations in relativistic heavy ion collisions**Supported by Fund Project of National Natural Science Foundation of China (11647093, 11405088, 11521064), Fund Project of Chengdu Technological University (2016RC004), the Major State Basic Research Development Program of China (2014CB845402) and the Ministry of Science and Technology (MoST) (2016YFE0104800)

Abstract

Taking doubly charged particles, positive-negative charge pair production and the effects of volume fluctuations into account, the Poisson baseline of the fluctuations of net-charge is studied. Within the Poisson baseline, the cumulants of net-charge are derived. Comparing to the Skellam baseline of net-charge, we infer that doubly charged particles broaden the distributions of net-charge, while positive-negative charge pairs narrow the distributions. Using the ratios of doubly charged particles and positive-negative charge pairs from neutral resonance decays to the total positive charges from THERMINATOR 2, the first four orders of moments and the corresponding moment products are calculated in the Poisson baseline for Au + Au collisions at at RHIC/STAR. We find that the standard deviation is mainly influenced by the resonance decay, while the third and fourth order moments and corresponding moment products are mainly modified and fit the data of RHIC/STAR much better after including the effects of volume fluctuations.