The Science of ALICE

Installation of ALICE TRT
Installation of one supermodule of the ALICE Transition Radiation Detector. Image © CERN
The ALICE experiment is dedicated to understanding the composition of matter as it existed shortly after the Big Bang. In these very early moments, the universe was at such a high temperature that protons, neutrons and atoms had not yet formed. Instead, the 10-microsecond-old universe was filled with a state of matter called the quark-gluon plasma, in which elementary particles such as gluons and quarks moved freely.

By studying the quark-gluon plasma, ALICE scientists hope to understand the strong nuclear force. This fundamental force binds quarks and gluons to create hadrons such as protons and neutrons. ALICE scientists study the properties of the quark-gluon plasma, as well as how the particles that make up the plasma behave and combine to form ordinary matter.

Tiny amounts of quark-gluon plasma, samples of the early universe, are created in the center of ALICE by collisions of lead nuclei. While the LHC spends most of its time accelerating protons, for at least one month out of every year it accelerates lead nuclei. Because each lead nucleus is made of hundreds of protons and neutrons, these collisions produce higher densities of hot matter than proton-proton collisions.

ALICE comic
Click image to read the ALICE comic.

To understand the behavior and properties of the quark-gluon plasma, scientists depend on ALICE’s high-precision particle detectors to record the results of as many as 50,000 lead-lead collisions per second.

ALICE is not the first experiment to look back in time by recreating the quark-gluon plasma. The study of matter at such high energy densities is known as ultra-relativistic heavy ion physics, a field that has been progressing for years at accelerators such as the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. ALICE is on the cutting edge of research in this field, the dedicated heavy ion experiment at the most powerful accelerator in the world.