Beam-Energy and System-Size Dependence of Dynamical Net Charge Fluctuations

TL;DR

This paper measures dynamical net charge fluctuations across various collision systems and energies, revealing their non-zero nature, modest energy dependence, weak system size dependence, and specific scaling behaviors, providing insights into the underlying particle production mechanisms.

Contribution

It provides new measurements of net charge fluctuations in different collision systems and energies, analyzing their dependence on system size, energy, and collision centrality, and examining their scaling properties.

Findings

Dynamical fluctuations are non-zero at all energies.

Weak dependence of fluctuations on beam energy and system size.

Violates $1/N_{ch}$ scaling but follows approximate $1/N_{part}$ scaling.

Abstract

We present measurements of net charge fluctuations in $Au + Au$ collisions at $\sqrt{s_{NN}} = $ 19.6, 62.4, 130, and 200 GeV, $Cu + Cu$ collisions at $\sqrt{s_{NN}} = $ 62.4, 200 GeV, and $p + p$ collisions at $\sqrt{s} = $ 200 GeV using the dynamical net charge fluctuations measure $\nu_{+-{\rm,dyn}}$. We observe that the dynamical fluctuations are non-zero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate $1/N_{ch}$ scaling, but display approximate $1/N_{part}$ scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation.