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Steven Vigdor
IU Cyclotron Facility

Hal Kibbey
IU Media Relations

Last modified: Tuesday, April 26, 2005

IU nuclear physicists go with the (perfect liquid) flow


BLOOMINGTON, Ind. -- What do you get when you heat an ordinary atomic nucleus to temperatures high enough to melt the neutrons and protons inside it -- temperatures reached during the first microseconds following the Big Bang birth of the universe?

You get a new state of matter -- a mix of quarks and gluons that is one of the most nearly perfect liquids ever observed.

Indiana University Physics Professor Steven Vigdor played a leading role in finding the surprising answer to this question, announced by Brookhaven National Laboratory during last week's meeting of the American Physical Society in Tampa, Fla. Atom-smashing experiments at Brookhaven's Relativistic Heavy Ion Collider on Long Island, N.Y., have yielded a new form of matter that behaves as an almost perfect liquid, flowing in a highly coordinated way with little or no friction.

The four major experimental collaborations at RHIC independently sifted through all of their results and all of the theoretical interpretations of those results to assess the clearest signals for this new state of matter. Their assessments will be published together in a single volume of the journal Nuclear Physics. Vigdor was the primary author of the assessment paper from the 500-member STAR collaboration, for which he has served as deputy spokesman. A group of nuclear physicists from IU, led by Vigdor, has played a strong role in the STAR collaboration.

In the RHIC experiments, gold nuclei are smashed into each other at extraordinarily high energies. Much of this energy of motion is converted to heat, and for a moment the residual matter, on a very small scale, reaches conditions resembling the earliest instants of the universe, even before the time when protons formed.

"It is highly surprising that out of the frictional flames of this violent collision of nuclei emerges an almost perfect liquid," Vigdor said. "Measurements from the STAR experiment have demonstrated that the matter flows as though all its parts are in close communication, requiring constant interactions among them. And yet these constant interactions do not appear to create friction that would sap the energy of coordinated motion. This may be an indication that the interacting parts have no internal structure of their own -- that the melting of protons and neutrons has released the quarks and gluons that are normally confined inside protons or neutrons."

It was predicted that quarks and gluons would break out of their proton/neutron prisons at sufficiently high temperatures, but most scientists expected the resulting matter to behave as a gas, with little interaction among its particles. That expectation was based on the novel feature that quarks and gluons tend to influence one another less and less the closer they are thrown together. But the matter produced at RHIC is decidedly not gas-like, Vigdor said, and its unique properties appear on the verge of revealing new mysteries of matter governed by the so-called strong interaction, the strongest of nature's fundamental forces.

Much of this research was funded by the U.S. Department of Energy, which operates Brookhaven National Laboratory. The participation of the Indiana University group in this research is funded by the National Science Foundation.