The quark gluon plasma is explored at LHC with the ion experiments there. A description can be found here.
In heavy-ion collisions, the first evidence for jets was seen in 2003 in the STAR and PHENIX experiments at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC) in the US. These jets showed a remarkable difference from those in simpler collisions, however. In the most striking measurement, STAR observed that one of the two back-to-back jets was invariably “quenched,” sometimes weakened and sometimes completely extinguished. The further a jet has to push through the dense fireball of a heavy-ion collision – 30 to 50 times as dense as an ordinary nucleus – the more energy it loses.
Jets are “hard probes”, by nature strongly interacting but moving so fast and with so much energy that they are often not completely absorbed by the surrounding quarks and gluons in the quark-gluon plasma. The degree of jet quenching – a figure that emerges in data from millions of collision events – plus the jets' orientation, directionality, composition, and how they transfer energy and momentum to the medium, reveal what’s inside the fireball and thus the properties of the quark-gluon plasma.
Recently the ALICE, ATLAS and CMS experiments at CERN’s Large Hadron Collider (LHC) have confirmed the phenomenon of jet quenching in heavy-ion collisions. The much greater collision energies at the LHC push measurements to much higher jet energies than are accessible at RHIC, allowing new and more detailed characterization of the quark-gluon plasma. Theoretical understanding of these measurements is challenging, however, and is one of the most important problems in quantum chromodynamics today.
