Charged hadron multiplicity fluctuations in Au+Au and Cu+Cu collisions from sqrt(s_NN) = 22.5 to 200 GeV

TL;DR

This paper investigates event-by-event fluctuations of charged hadron multiplicity in heavy ion collisions at various energies, finding that fluctuations decrease with centrality and show no signs of critical phenomena.

Contribution

It provides a comprehensive analysis of multiplicity fluctuations across different collision systems and energies, correcting for geometric effects and comparing to baseline models.

Findings

Dynamical fluctuations decrease with increasing centrality.

Fluctuations are consistent with superposition of nucleon-nucleon collisions.

Heavy ion data show weak clustering properties.

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 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 non-dynamical 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. An analysis of Negative Binomial Distribution fits to the multiplicity distributions demonstrates that the heavy ion data exhibit weak clustering properties.