Relativistic heavy-ion collisions

Article By:

Sorensen, Soren P. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee.

Last reviewed:August 2020

DOI:https://doi.org/10.1036/1097-8542.579850

Collisions between heavy atomic nuclei at relative velocities close to the speed of light. These high-energy nuclear collisions are usually divided into two different domains, relativistic and ultrarelativistic collisions, depending on whether the kinetic energy per nucleon (the generic name for protons and neutrons) is either close to the rest mass of the nucleon, about 1 GeV (relativistic collisions), or much larger than the nucleon rest mass (ultrarelativistic collisions). When two nuclei collide at these high energies, some of the nucleons in each nucleus, called spectators, will continue their motion unaffected, while other nucleons, called participants, will strike one or several nucleons in the other nucleus (see illustration). In the overlap region, a hot and dense fireball will develop. It is the properties of this fireball of nuclear matter that is the primary research goal of most experiments using high-energy heavy-ion collisions.

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