In high-energy physics, jet quenching is a phenomenon that can occur in the collision of ultra-high-energy particles.
In the context of high-energy hadron collisions, quarks and gluons are collectively called partons.
The hot, dense medium produced in the collisions is also composed of partons; it is known as a quark–gluon plasma (QGP).
High-energy nucleus–nucleus collisions make it possible to study the properties of the QGP medium through the observed changes in the jet fragmentation functions as compared to the unquenched case.
Indeed, in November 2010 CERN announced the first direct observation of jet quenching, based on experiments with heavy-ion collisions, which involved ATLAS, CMS and ALICE.