Frontemare di Trieste
Istituto Nazionale di Fisica Nucleare
Sezione di Trieste

Heavy Ions at Ultra-Relativistic Energies at LHC: ALICE

ALICE is a collaboration involving more than 1000 researchers from over 30 nations. The experiment studies the interaction between lead ions accelerated by the large Hadron collider (LHC) to ultra-relativistic energies. Its goal is the study of quark-gluon plasma and associated phenomena. Thanks to its performances, the detector also makes a significant contribution to results of the physics of p+p interactions.

The apparatus consists of a solenoidal magnet and several different detectors, mostly located inside the magnet in cylindrical symmetry around the axis of the LHC's beams. This allows for high-efficiency detection of the multitude of different particles produced in high-energy ion-ion collision.

The detector is approximately 20 meters in long and has a circumference of 16 meters. Starting from the section near the zone of interaction and moving radially outwards, we find: the vertex detector consisting of 6 cylindrical layers of silicon pixels, silicon drift and silicon micro-strip detectors (Trieste's researchers played a central role in the realization of the latter two), a gas tracking chamber for high-momentum charged particles, a time of flight detector, a photon spectrometer, and an electromagnetic calorimeter.

In addition, outside the magnet there is a muon spectrometer, detectors dedicated to the trigger and to calorimetric measurements at small angles, and cosmic ray monitors.

The results of studying the phenomena associated with the quark-gluon plasma contribute to a better and wider understanding of the nature of the strong interaction: this could not be obtained with reactions involving only a few nucleons in the entrance channel.

Moreover, they provide important results with which to compare the predictions regarding the evolution of the universe in its first moments after the Big Bang, in fact, high-energy lead-ion collisions are actually described as Little Bangs, namely as Big Bangs very much in miniature.

Visit the site of experiment ALICE.

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