Charged hadron multiplicity fluctuations in $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ collisions from $\sqrt{{s}_{\mathit{NN}}}=22.5$ to 200 GeV

Charged hadron multiplicity fluctuations in $Au + Au$ and $Cu + Cu$ collisions from $\sqrt{s_{NN}} = 22.5$ to 200 GeV

A. Adare et al. (PHENIX Collaboration)

Phys. Rev. C 78, 044902 – Published 7 October 2008

Abstract

A comprehensive survey of event-by-event fluctuations of charged hadron multiplicity in relativistic heavy ions is presented. The survey covers $Au + Au$ collisions at $\sqrt{s_{NN}} = 62.4$ and 200 GeV, and $Cu + Cu$ collisions at $\sqrt{s_{NN}} = 22.5, 62.4$ , and 200 GeV. Fluctuations are measured as a function of collision centrality, transverse momentum range, and charge sign. After correcting for nondynamical fluctuations due to fluctuations in the collision geometry within a centrality bin, the remaining dynamical fluctuations expressed as the variance normalized by the mean tend to decrease with increasing centrality. The dynamical fluctuations are consistent with or below the expectation from a superposition of participant nucleon-nucleon collisions based upon $p + p$ data, indicating that this dataset does not exhibit evidence of critical behavior in terms of the compressibility of the system. A comparison of the data with a model where hadrons are independently emitted from a number of hadron clusters suggests that the mean number of hadrons per cluster is small in heavy ion collisions.