Physics

Medium-Sized Bang

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Science  24 Dec 2010:
Vol. 330, Issue 6012, pp. 1725
DOI: 10.1126/science.330.6012.1725-a
CREDIT: COURTESY THE ALICE EXPERIMENT AT CERN

Most models that strive to describe the state of our universe after the Big Bang predict the existence of the quark-gluon plasma microseconds after the beginning of time. High temperatures are thought to have supported a state wherein the constituents of atomic nucleons—quarks and gluons—existed unbound. In an effort to recreate such conditions, researchers earlier collided gold ions using the Relativistic Heavy Ion Collider (RHIC) and found that the state of matter they created behaved much more like a liquid than a gas. Now, similar experiments have been carried out using the Large Hadron Collider (LHC) to collide lead ions at even higher energies than those achieved at RHIC. The results were collected and analyzed by two groups. Aamodt et al. (ALICE collaboration) found that at these higher energies and temperatures, the quark-gluon plasma still behaves like a (nearly perfect) liquid, implying that it is a strongly interacting system. This conclusion was further corroborated by Aad et al. (ATLAS collaboration), who determined that jets of particles produced by the collisions in the plasma are strongly quenched by their interaction with the surrounding medium.

Phys. Rev. Lett. 105, 252302; 252303 (2010).

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