Collaborating for a "Perfect" Scan of Nuclear Matter
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To continue exploring the nature of this perfect liquid, RHIC physicists are building on their remarkable early discoveries to mount precision studies with newly refined experimental and theoretical techniques. A near-term upgrade, expected to increase the machine’s collision rate and improve the sensitivity of detectors, would make critical measurements at RHIC more quantitative, allowing scientists to learn more from theory-experiment comparisons of the properties of the perfect liquid. For example, scientists can examine the applicability of “string theory,” which has suggested completely unanticipated connections between the strongly interacting matter produced at RHIC and gravitational systems such as black holes.
But physicists will need the assistance of multiple scientific facilities to determine the so-called phase diagram of nuclear matter. A phase diagram shows the boundaries between different types of the same substance as external conditions, such as pressure and temperature, change. One of the best-known phase diagrams illustrates what happens to water as it freezes in an ice cube tray or turns to steam while boiling in a pot on the stove. For nuclear matter, the phase diagram aims to show the boundary between normal matter, composed of compact neutrons and protons, and a system of liberated quarks and gluons.
Exploring the phase diagram of nuclear matter requires much more than kitchen-sink experiments. To reach the extreme conditions required to “melt” normal matter into a soup of quarks and gluons, which happens at temperatures more than 100,000 times hotter than the center of the sun, scientists need an array of accelerators capable of creating collisions of varying energies.
The Large Hadron Collider (LHC), a powerful accelerator now coming online in Switzerland, is expected to reveal how the perfect liquid evolves at even higher temperatures than are produced at RHIC. Although the machine’s primary focus is to create new, massive particles by colliding beams of protons, the LHC also will collide lead ions and devote a short amount of its run time — about four weeks per year — to nuclear physics.
“We’re curious to find out if matter analogous to the perfect liquid can be created at even higher temperatures, and if so, what it looks like,” said Brookhaven’s Physics Department Chair Tom Ludlam. “Will it become even more perfect? Or will it actually behave like a gas for a fraction of its tiny lifetime? We may be able to determine that from studies at the LHC.”