ALICE (A Large Ion Collider Experiment) is a dedicated heavy-ion experiment at the 27 km circumference Large Hadron Collider (LHC) at CERN.
It studies the thermodynamic properties of quarks and gluons at extreme energy densities produced when two lead nuclei are collided in the LHC. QCD is the theory that describes how quark and gluons interact.
Normally, quarks and gluons are confined inside hadrons such as the proton and the neutron that make up the atomic nuclei. However, QCD predicts that, at sufficiently high densities, there will be a transition from hadronic matter, to a plasma of deconfined quarks and gluons - the quark-gluon plasma (QGP). This transition occured in the early universe micro-seconds after the Big Bang and the goal of the experiment at CERN is to reproduce and study the properties of this transtion.
The ALICE collaboration has built and operates the ALICE detector, which is optimized for the study of the thermodynamic properties of the QGP. This involves big precision measurements of bulk properties and particle identification.
ALICE is the only dedicated heavy-ion experiment at the LHC but it extends a long tradition of experiments done at lower collision energy both at Brookhaven national lab in the US and at CERN.