Heavy Ion physics with the ALICE experiment at the CERN LHC

TL;DR

This paper reviews the ALICE experiment's initial results from heavy ion collisions at CERN LHC, highlighting detector design, operation, and findings that suggest the formation of a strongly interacting quark-gluon plasma.

Contribution

It provides the first comprehensive overview of ALICE's design, performance, and initial physics results at the LHC, including insights into high-density matter behavior.

Findings

pp results challenge existing QCD models

Pb-Pb collisions indicate a strongly interacting quark-gluon plasma

High-density matter behaves like an almost perfect liquid

Abstract

After close to 20 years of preparation, the dedicated heavy ion experiment ALICE took first data at the CERN LHC accelerator with proton collisions at the end of 2009 and with lead nuclei at the end of 2010. After a short introduction into the physics of ultra-relativistic heavy ion collisions, this article recalls the main design choices made for the detector and summarizes the initial operation and performance of ALICE. Physics results from this first year of operation concentrate on characterizing the global properties of typical, average collisions, both in pp and nucleus-nucleus reactions, in the new energy regime of LHC. The pp results differ, to a varying degree, from most QCD inspired phenomenological models and provide the input needed to fine-tune their parameters. First results from Pb-Pb are broadly consistent with expectations based on lower energy data, indicating that high density matter created at LHC, while much hotter and larger, still behaves like a very strongly interacting, almost perfect liquid.