Looking for the Phase Transition—Recent NA61/SHINE Results

Ludwik Turko

doi:10.3390/universe4030052

Abstract

The fixed-target NA61/SHINE experiment at the CERN Super Proton Synchrotron (SPS) seeks to find the critical point (CR) of strongly interacting matter as well as the properties of the onset of deconfinement. The experiment provides a scan of measurements of particle spectra and fluctuations in proton–proton, proton–nucleus, and nucleus–nucleus interactions as functions of collision energy and system size, corresponding to a two-dimensional phase diagram (T- μ B ). New NA61/SHINE results are shown here, including transverse momentum and multiplicity fluctuations in Ar+Sc collisions as compared to NA61 p+p and Be+Be data, as well earlier NA49 A+A results. Recently, a preliminary effect of change in the system size dependence, labelled as the “percolation threshold” or the “onset of fireball”, was observed in NA61/SHINE data. This effect is closely related to the vicinity of the hadronic phase space transition region and will be discussed in the text.

Highlights

The NA61/SHINE, understood as the Super Proton Synchrotron (SPS) Heavy Ion and NeutrinoExperiment, is a continuation and extension of the NA49 experiment [1,2]
The strong interaction programme of the NA61/SHINE is dedicated to the study of the onset of deconfinement and the search for the critical point (CR) of hadronic matter, related to the phase transition between hadron gas (HG) and quark–gluon plasma (QGP)
This is just the kinematical region where NA49 data indicate the onset of deconfinement in central Pb+Pb collisions, observing structures in the energy dependence of hadron production in central Pb+Pb collisions which are not observed in hadron interactions [23,24]

Summary

Introduction

The NA61/SHINE, understood as the Super Proton Synchrotron (SPS) Heavy Ion and Neutrino. The NA49 experiment studied hadron production in Pb+Pb interactions, while the NA61/SHINE collects data varying beam energy within the range of 13A–158A GeV and varying sizes of the colliding systems. A more detailed exploration of QCD phase diagram would need both new experimental data with extended detection capabilities and improved theoretical models [16] Another intriguing and far reaching possibility is the Big Bang phase transition scenario, referred to by Edward Witten as the “cosmic separation of phases” [17]. Beyond cosmological effects (little/tepid inflation) such a possibility would change our understanding of the hadronization effect in HIC processes

Irregularities—The Horn

Irregularities—The Step

Fluctuations

System Size Dependence

Conclusions