NA49/NA61: results and plans on beam energy and system size scan at the CERN SPS

TL;DR

This paper reviews results from NA49 and NA61/SHINE experiments at CERN SPS on the onset of deconfinement and the search for the critical point in relativistic nucleus-nucleus collisions, highlighting key findings and future plans.

Contribution

It summarizes evidence for the energy threshold of quark-gluon plasma formation and details the systematic search for the critical point using beam energy and system size scans.

Findings

Evidence for the energy threshold of quark-gluon plasma at around 30A GeV.

Large fluctuations observed at 158A GeV suggest the possible location of the critical point.

NA61/SHINE's ongoing scan aims to confirm or refute the critical point hypothesis.

Abstract

This paper presents results and plans of the NA49 and NA61/SHINE experiments at the CERN Super Proton Synchrotron concerning the study of relativistic nucleus-nucleus interactions. First, the NA49 evidence for the energy threshold of creating quark-gluon plasma, the onset of deconfinement, in central lead-lead collisions around 30A GeV is reviewed. Then the status of the NA61/SHINE systematic study of properties of the onset of deconfinement is presented. Second, the search for the critical point of strongly interacting matter undertaken by both experiments is discussed. NA49 measured large fluctuations at the top SPS energy, 158A GeV, in collisions of light and medium size nuclei. They seem to indicate that the critical point exists and is located close to baryonic chemical potential of about 250 MeV. The NA61/SHINE beam energy and system size scan started in 2009 will provide evidence for the existence of the critical point or refute the interpretation of the NA49 fluctuation data in terms of the critical point.