Onset of deconfinement and search for the critical point of strongly interacting matter at CERN SPS energies

TL;DR

This paper discusses the search for the QCD phase transition and critical point at CERN SPS energies, highlighting experimental signals indicating the onset of deconfinement and fluctuations near the critical point.

Contribution

It presents experimental evidence from NA49 indicating the onset of deconfinement and explores fluctuation signals related to the critical point in the QCD phase diagram.

Findings

Qualitative changes in hadronic observables at SPS energies

Evidence of the onset of deconfinement in Pb+Pb collisions

Fluctuation signals potentially indicating the critical point

Abstract

The exploration of the QCD phase diagram particularly the search for a phase transition from hadronic to partonic degrees of freedom and possibly a critical endpoint, is one of the most challenging tasks in present heavy-ion physics. As observed by the NA49 experiment, several hadronic observables in central Pb+Pb collisions at the CERN SPS show qualitative changes in their energy dependence. These features are not observed in elementary interactions and indicate the onset of a phase transition in the SPS energy range. The existence of a critical point is expected to result in the increase of event-by-event fluctuations of various hadronic observables provided that the freeze-out of the measured hadrons occurs close to its location in the phase diagram and the evolution of the final hadron phase does not erase the fluctuations signals. A selection of NA49 results on di-pion and proton intermittency from the scan of the phase diagram will be discussed.