Probing the Quark-Gluon Phase Transition with Correlations and Fluctuations in Heavy Ion Collisions from the STAR Experiment

TL;DR

This paper investigates particle correlations and fluctuations in heavy ion collisions to identify signals of the quark-gluon plasma phase transition and the QCD critical point, using data from the STAR experiment across various systems and energies.

Contribution

It provides new measurements of multiplicity correlations and fluctuations in heavy ion collisions, comparing results with theoretical models to explore the quark-gluon phase transition and critical phenomena.

Findings

Correlation strength remains constant in central high-energy A+A collisions.

Peripheral and lower-energy collisions show maximum correlations at midrapidity.

Model comparisons reveal discrepancies with experimental data, indicating complex underlying physics.

Abstract

The measurement of particle correlations and fluctuations has been suggested as a method to search for the existence of a phase transition in relativistic heavy ion collisions. If quark-gluon matter is formed in the collision of relativistic heavy ions, measuring these correlations could lead to a determination of the presence of partonic degrees of freedom within the collision. Additionally, non-statistical fluctuations in global quantities such as baryon number, strangeness, or charge may be observed near a QCD critical point. Results for short and long-range multiplicity correlations (forward-backward) are presented for several systems (Au+Au and Cu+Cu) and energies (e.g. $\sqrt{s_{NN}}$ = 200, 62.4, and 22.4 GeV). For the highest energy central A+A collisions, the correlation strength maintains a constant value across the measurement region. In peripheral collisions, at lower energies, and in pp data, the maximum appears at midrapidity. Comparison to models with short-range (HIJING) and both short and long-range interactions (Parton String Model) do not fully reproduce central Au+Au data. Preliminary results for K/$\pi$ fluctuations are also shown as a function of centrality in Cu+Cu collisions at $\sqrt{s_{NN}}$ = 22.4 GeV.