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managed for the U.S. Department of Energy
by Brookhaven Science Associates, a company
founded by Stony Brook University and Battelle

Cooking Up Quark Soup

The basic way that RHIC aims to create the QGP is by achieving a phase transition — heating up ordinary nuclear matter (in this case gold nuclei) by slamming tiny bits of it (two nuclei at a time) together at near the speed of light so that the nuclear components undergo a change of state — similar to the way that ice cubes melt to form liquid water or liquid water boils to form steam.

At the time of each collision, most of the energy of the usually cold nuclei is converted to heat, which can then transform the matter to a quark-gluon plasma. In QGP, the quarks and gluons are so hot and so dense that they move around in a hot, seething soup of unbound quarks and gluons. All this happens in a tiny fraction of a second, or 0.00000000000000000000001 seconds, in decimal form.

This transition follows the collision of two gold nuclei and can be thought of as moving in time along a path across a “map” of the nuclear phases — the nuclear phase diagram, which plots energy and density. When the temperature and density have passed the phase boundary into QGP, the properties of the plasma are expected to reveal new behaviors not seen in everyday nuclear matter.

“So far,” reports Kirk, “We are confident that the necessary regions of the nuclear phase map have been visited, including the hot, dense regime where quark-gluon plasma is expected to be found.” The thermalized energy density achieved so far is at least 30 times the comparable energy density in nuclei at rest, and scientists have some indications that the temperature reaches more than seven billion times room temperature.

But even with those incredible measurements, it is still too early to proclaim that the QGP phase has been reached. Explain Kirk, “The proof of quark-gluon plasma observation will require a number of distinct measurements, all showing self-consistent behavior with the properties ascribed to the quark gluon plasma. Some of these measurements have already been made at this early point in the RHIC program, but some are still in the future.”

Even after the scientists definitively create QGP, there will still be much to discover about its properties and behavior, using a variety of experimental techniques.

NEXT> Gathering Additional Evidence

The U.S. Department of Energy's Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists. The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.