Brookhaven and the LHC

Collaborating for a "Perfect" Scan of Nuclear Matter

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The LHC, RHIC, and FAIR will each explore a different section of the nuclear matter phase diagram, which is depicted in this graphic. As temperature and density change, so does the boundary between normal hadronic matter, composed of neutrons and protons, and a system of unconfined quarks and gluons. The critical point is an as-yet-undiscovered landmark; the transition from hadron gas to quark-gluon plasma is predicted to be smooth at densities to the left of the critical point, but sharp on the other side, at higher densities.

To further explore the nuclear matter phase diagram, future RHIC experiments will demand lower energy collisions than produced in the past. Researchers are particularly interested in using RHIC to pinpoint the location of the “critical point,” a threshold of temperature and density above which there is no sharp transition between two phases. On one side of the critical point associated with nuclear matter, there is an obvious difference between normal matter and a substance of unconfined quarks and gluons, and the transition from one phase to the other is sharp. But on the other side, the two phases can coexist and the transition from one to the other is a smooth crossover. So far, collisions at RHIC result in temperatures well above the critical point. With versatility in beam species and energies, and long running times for collisions of heavy nuclei at lower temperatures, RHIC is well positioned to uncover this telltale transition point, Ludlam said.

“Pinning down a critical point in the phase diagram is the best way to understand how quarks and gluons work together over large volumes to form the perfect liquid,” Ludlam said. “If we find it, experimental data on both sides of the point will reveal a great deal about the fundamental processes that have produced the matter we see in our universe today.”

In addition to the LHC and RHIC, one more facility will soon enter the energy-scanning mission. GSI, the German research center for heavy ion physics, is currently building the Facility for Antiproton and Ion Research (FAIR), a series of synchrotrons, storage rings, and detectors meant to study numerous aspects of physics. FAIR, scheduled to begin operating in 2016, will use extremely high nuclear densities in a low-energy scan that could map out the nuclear matter phase diagram well to the right of the critical point.

 “We need specialized information from each of these facilities to paint a complete picture of nuclear matter,” Ludlam said, adding that “to make sense of what will be seen at very high energies at the LHC and very low energies at FAIR, physicists need to know what has happened and will happen at RHIC. As data emerge from all three of these world-class facilities, we will enter a golden age of heavy ion physics.”