Results from the first heavy ion run at the LHC

TL;DR

The first heavy ion collisions at the LHC in 2010 marked a new era in ultra-relativistic heavy ion physics, revealing a hot, dense quark-gluon plasma that behaves like a nearly perfect liquid, with some surprising experimental results.

Contribution

This paper reports the initial results from the LHC heavy ion program, demonstrating the creation of a quark-gluon plasma at unprecedented energies and conditions.

Findings

High-density matter behaves like a nearly perfect liquid.

Surprising particle ratios and jet-quenching effects observed.

Evidence of quarkonia suppression at LHC energies.

Abstract

Early November 2010, the LHC collided for the first time heavy ions, Pb on Pb, at a centre-of-mass energy of 2.76 TeV/nucleon. This date marked both the end of almost 20 years of preparing for nuclear collisions at the LHC, as well as the start of a new era in ultra-relativistic heavy ion physics at energies exceeding previous machines by more than an order of magnitude. This contribution summarizes some of the early results from all three experiments participating in the LHC heavy ion program (ALICE, ATLAS, and CMS), which show that the high density matter created at the LHC, while much hotter and larger, still behaves like the very strongly interacting, almost perfect liquid discovered at RHIC. Some surprising and even puzzling results are seen in particle ratios, jet-quenching, and Quarkonia suppression observables. The overall experimental conditions at the LHC, together with its set of powerful and state-of-the-art detectors, should allow for precision measurements of quark-gluon-plasma parameters like viscosity and opacity.