Viewing the Chemical Evolution of the Quark-Gluon Plasma with Charge Balance Functions

TL;DR

This paper uses charge balance functions to analyze the timing of charge creation in relativistic heavy ion collisions, distinguishing early QGP formation from later hadronization, and estimates quark densities consistent with thermalization.

Contribution

It introduces a method to differentiate charge creation waves in heavy ion collisions using charge balance functions and estimates quark densities in the QGP.

Findings

Early and late charge creation waves are distinguishable.

Quark densities in the QGP agree within 20% of thermalization expectations.

Charge correlations reveal the timing of charge production.

Abstract

Correlations from charge conservation are affected by when charge/anticharge pairs are created during the course of a relativistic heavy ion collision. For charges created early, balancing charges are typically separated by the order of one unit of spatial rapidity by the end of the collision, whereas those charges produced later in the collision are far more correlated. By analyzing correlations from STAR for different species, I show that one can distinguish the two separate waves of charge creation expected in a high-energy collision, one at early times when the QGP is formed and a second at hadronization. Further, I extract the density of up, down and strange quarks at in the QGP and find agreement at the 20% level with expectations for a chemically thermalized plasma.