Hottest temps ever at LHC, and more hints about early Universe:
Washington, DC—This week is the Quark Matter 2012 (QM2012) conference—the preeminent meeting for those studying high-energy collisions between heavy ions. I attended a number of talks on Monday, August 13, during which researchers announced the major new results from the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory and the Large Hadron Collider (LHC) at CERN. The conference offered fresh insights on the transition between ordinary matter and the soup of quarks that existed in the early Universe—including a tantalizing hint that might tell us about why the modern cosmos has more matter than antimatter.
We recently ran a detailed review of heavy-ion physics; here's an executive summary. Heavy nuclei (lead at LHC, gold, copper, and uranium at RHIC) are completely stripped of electrons, leaving massive, positively charged ions. These are accelerated to well over 99 percent of the speed of light and smashed into each other. If the energy is sufficiently high, the protons and neutrons in the nuclei "melt" into their constituent quarks and gluons. The result is a substance known as the quark-gluon plasma (QGP), which theory predicts existed during the first 10 microseconds after the Big Bang.
While the hunt for the Higgs boson has dominated press coverage of the LHC, the collider also performs heavy ion experiments using lead (Pb+Pb). In addition to the ATLAS and CMS detectors, which are used both for proton-proton and heavy ion collisions, LHC has a dedicated heavy ion detector named ALICE (A Large Ion Collider Experiment, pronounced "ahLEES"). The two active detectors at RHIC are PHENIX (Pioneering High-Energy Nuclear Interacting Experiment) and STAR (Solenoidal Tracker at RHIC). These study the products of collisions between gold ions (Au+Au); in the most recent experiments, researchers have added gold and copper asymmetric collisions (Au+Cu) and uranium (U+U). The two major colliders are complimentary in many aspects: the LHC has a larger temperature range and can reach lower density, while RHIC is able to explore much higher baryon densities.
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