University of Heidelberg
GSI

ALICE

ISOQUANT

The ALICE Detector at the LHC



Apart from the two high luminosity experiments ATLAS and CMS as well as the LHCb detector for the study of beauty physics, the LHC has one experiment dedicated to Pb-Pb ion operation which is called A Large Ion Collider Experiment (ALICE). ALICE is optimised to investigate the physics of strongly interacting matter and the high energy density environment which is produced in Pb-Pb collisions. The experiment is designed to be a general-purpose detector measuring a wide range of physics observables.

The running of the coupling constant in Quantum Chromodynamics (QCD), which is the quantum field theory describing the strong interaction, gives rise to the colour confinement at small momentum transfer. The quarks and gluons, which are the constituents of the matter surrounding us, are therefore only observed as confined states, the hadrons.
In heavy-ion collisions, where high temperatures and high densities of matter are reached, hadrons begin to interpenetrate each other and a new state of matter is expected to be formed, in which quarks and gluons can be considered free. This state is called quark-gluon plasma (QGP). The existence and the description of this phase of matter is a central issue in the understanding of QCD.
Just shortly after the big bang, before hadrons were formed out of quarks and gluons, the universe was in such a state of extremely high temperature and energy density.
Since the phase transition from confinement to deconfinement at high temperatures is expected to be reached in heavy-ion collisions it is possible to probe the QGP by measuring the particles evolving from the collisions between heavy ions.
With the ALICE detector it is therefore possible to study the properties and the evolution of the QGP and to observe how it gives rise to the production of the particles that are the constituents of the matter in our universe today.

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