Recent results on event-by-event fluctuations from the RHIC Beam Energy Scan program in the STAR experiment

TL;DR

This paper reviews recent results from the STAR experiment's RHIC Beam Energy Scan, focusing on event-by-event fluctuations as probes for the QCD phase transition and critical point, highlighting new findings on particle ratios and correlations across energies.

Contribution

It presents new measurements of fluctuations and correlations in heavy-ion collisions, advancing the search for the QCD critical point and phase transition signatures.

Findings

Non-monotonic behavior observed in higher moments of conserved quantities.

Dynamical fluctuations in particle ratios show energy dependence.

Results support the existence of a de-confined QCD matter phase.

Abstract

Event-by-event fluctuations of global observables in relativistic heavy-ion collisions are studied as probes for the QCD phase transition and as tools to search for critical phenomena near the phase boundary. Dynamical fluctuations in mean transverse momentum, identified particle ratios and conserved quantities (such as net-charge, net-baryon) are expected to provide signatures of a de-confined state of matter. Non-monotonic behavior in the higher-moments of conserved quantities as a function of beam energy and collision centrality are proposed as signatures of the QCD critical point. To study the QCD phase transition and locate the critical point, the STAR experiment at RHIC has collected a large amount of data for Au+Au collisions from $\sqrt{s_{NN}} = 7.7-200$~GeV in the RHIC Beam Energy Scan (BES) program. We present the recent beam energy scan results on dynamical fluctuations of particle ratios and two-particle transverse momentum correlations at mid-rapidity. Higher-moments of the net-charge and net-proton multiplicity distributions as a function of beam energy will be presented. We give a summary of what has been learnt so far and future prospectives for the BES-II program.