Heavy Ions, Experimental Overview

TL;DR

This paper reviews recent experimental results from heavy-ion collisions at ultra-relativistic energies, highlighting insights into initial collision geometry, particle production, and evidence for quark-gluon plasma formation.

Contribution

It provides a comprehensive overview of experimental measurements across various probes, including electroweak, soft, and hard particles, and discusses new findings on deconfinement and particle production mechanisms.

Findings

Electroweak probes constrain initial geometry and nuclear PDFs.

Light-flavour hadrons follow a universal temperature and collective motion.

Evidence for deconfinement from J/ψ meson studies.

Abstract

This article gives an overview of recent highlights from experimental measurements of heavy-ion collisions at ultra-relativistic energies: Measurements of electroweak probes constrain both the initial collision geometry and the nuclear parton distribution functions. Results from soft particle production show that the abundance of light-flavour hadrons from pions up to hypertriton and $^4$He can be described by a universal temperature and that these participate in the collective motion of the system. There are hints of these effects also in small systems, which will be further investigated in future to understand the underlying mechanisms. Studies of hard probes, such as heavy quarks and jets show that parton energy loss plays an important role in heavy-ion collisions. Differential measurements of J/$\psi$ mesons elucidate their production mechanism, i.e.\ regeneration, and give evidence for deconfinement in Pb--Pb collisions at LHC full energy. The large data samples at the LHC enable studies of rare probes such as $\chi_{\rm c1}$(3872) and top--anti-top production. Further, measurements of antinuclei cross sections can provide input for dark matter searches.