The QCD Phase Diagram from Statistical Model Analysis

TL;DR

This paper analyzes how various final state interactions affect the statistical model's freeze-out curve, which aims to reflect the QCD phase transition, and discusses implications of a broad crossover transition on hadronization observables.

Contribution

It introduces a method to correct for annihilation effects using UrQMD and explores how different hadronization observables may freeze out at different temperatures.

Findings

Baryon-antibaryon annihilation significantly shifts the freeze-out curve.

UrQMD can quantify and correct for annihilation effects.

Different observables may indicate different freeze-out temperatures.

Abstract

Ideally, the Statistical Hadronization Model (SHM) freeze-out curve should reveal the QCD parton-hadron phase transformation line in the ($T$,$\mu_B$) plane. We discuss the effects of various final state interaction phenomena, like baryon-antibaryon annihilation, core-corona effects or QCD critical point formation, which shift or deform the SHM freezeout curve. In particular, we present a method to remove the annihilation effects by quantifying them with the microscopic hadron transport model UrQMD. We further discuss the new aspects of hadronization that could be associated with the relatively broad cross-over phase transformation as predicted by lattice-QCD theory at low $\mu_B$. That opens up the possibility that various observables of hadronization, e.g. hadron formation or susceptibilities of higher order (related to grand canonical fluctuations of conserved hadronic charges) may freeze out at different characteristic temperatures. This puts into question the concept of a universal \textit{(pseudo-)critical} temperature, as does the very nature of a cross-over phase transformation.