Type: Article
Publication Date: 2016-03-10
Citations: 37
DOI: https://doi.org/10.1103/physrevc.93.034907
The effects of kinematic cuts on electric charge fluctuations in a gas of charged particles are discussed. We consider a very transparent example of an ideal pion gas with quantum statistics, which can be viewed as a multicomponent gas of Boltzmann particles with different charges, masses, and degeneracies. Cumulants of net electric charge fluctuations ${\ensuremath{\chi}}_{n}^{Q}$ are calculated in a static and expanding medium with flow parameters adjusted to the experimental data. We show that the transverse momentum cut, ${p}_{{t}_{\text{min}}}\ensuremath{\le}{p}_{t}\ensuremath{\le}{p}_{{t}_{\text{max}}}$, weakens the effects of Bose statistics, i.e., contributions of effectively multicharged states to higher order moments. Consequently, cuts in ${p}_{t}$ modify the experimentally measured cumulants and their ratios. We discuss the influence of kinematic cuts on the ratio of mean and variance of electric charge fluctuations in a hadron resonance gas, in the light of recent data from the STAR and PHENIX Collaborations. We find that the different momentum cuts of ${p}_{{t}_{\text{min}}}=0.2$ GeV (STAR) and ${p}_{{t}_{\text{min}}}=0.3$ GeV (PHENIX) are responsible for more than 30% of the difference between these two data sets. We argue that the ${p}_{t}$ cuts imposed on charged particles will influence the normalized kurtosis ${\ensuremath{\kappa}}_{Q}{\ensuremath{\sigma}}_{Q}^{2}={\ensuremath{\chi}}_{4}^{Q}/{\ensuremath{\chi}}_{2}^{Q}$ of the electric charge fluctuations. In particular, the reduction of ${\ensuremath{\kappa}}_{Q}{\ensuremath{\sigma}}_{Q}^{2}$ with increasing ${p}_{{t}_{\text{min}}}$ will lead to differences between PHENIX and STAR data of $\mathcal{O}(6%)$, which currently are buried under large statistical and systematic errors. We furthermore introduce the relation between momentum cutoff and finite volume effects, which is of relevance for the comparison between experimental data and lattice QCD calculations.