Researchers find quarks like those from Big Bang

By Ian Hoffman, STAFF WRITER

In this world, there's no such thing as a free quark.

These basic bits of matter are prisoners, locked tightly to one another -- three quarks inside each of the nuclear particles that make up jellyfish, volcanoes and humans.

But Berkeley physicist Xin-Nian Wang is virtually certain that scientists have produced a new breed of matter, a soup of loose quarks last seen 14 billion years ago, a few millionths of a second after the Big Bang.

Dubbed the "quark-gluon plasma," it's billions of times hotter than the heart of the sun and as dense as the core of a neutron star.

If Wang is right, the plasma winks into existence a few million times a year, when atoms of gold smash head-on inside the Relativistic Heavy Ion Collider at Brookhaven National Laboratory in New York.

"There's really an accumulation of a vast amount of evidence for its creation," Wang said.

No one has ever seen the plasma. If it exists, the plasma lasts a trillionth of a trillionth of a second. And the chief evidence for its creation is what scientists don't see. Precisely what nuclear physicists have created and what it means are ripe for debate this week in the Oakland Convention Center, at this year's Quark Matter conference.

"This entire week, people will be fighting over whether the plasma really was there," says Michigan State physicist Gary Westfall.

Early in the construction of the Long Island collider, better known as RHIC, a handful of European scientists predicted horrors. Bashing gold atoms head-to-head could give birth to a black hole. It could devour Manhattan, then the world.

In fact, smacking heavy atoms together produces exactly what scientists expected -- thousands of subatomic shrapnel, blasting away from the collision in all directions. Scientists call the behavior of these expanding frag-ments "collective flow," a phenomenon not unlike the expansion of the universe after the Big Bang.

Scientists first saw evidence of collective flow at Lawrence Berkeley Laboratory's Bevalac, a mainstay machine for nuclear physics in the 1980s, and they began thinking about how to create the quark-gluon plasma.

"It all started here at Berkeley," said Horst Stocker, a physics professor at the University of Frankfurt.

At first, theorists conceived of the plasma as a gas. In 1991, Wang and former Berkeley lab colleague Miklos Gyulassy predicted somewhat sterner, "stickier" stuff, more like nuclear molasses.

It would be undetectable, except by inference: As subatomic particles inside the gold nuclei smacked together, they would blast apart in two sprays, called jets. If the plasma existed, it would be hot and dense enough to slow at least one spray down. This "jet quenching" is what scientists have seen repeatedly since 2000 at Brookhaven's collider, watching gold collisions through highly sophisticated instruments designed to identify thousands of fragments and their destinies.

If the collisions simply create a hot mass of nuclear particles, then other particles should knock around inside the mass, as if rocketing through a bunch of marbles. But if the collisions create hot enough conditions to break down the atomic nuclei -- to make the quarks inside "de-confine" from one another -- then the bunch of marbles turn to molten glass and slow down any intruder.

Particles of various kinds act differently in the plasma. Scientists now are trying to pinpoint the nuclear fragments that they can see and that will reveal the most about the stuff created in the collision.

"It's sort of hard to tell. The probes and the medium are sort of made of the same stuff," said Brookhaven physics chairman Sam Aronson.

Even if the plasma has been found, scientists still must understand it to add appreciatively to their theoretical notions of how matter forms and how the universe evolved in its infancy.

"There's a very strong feeling that more measurements need to be done," Aronson said.

"We have to give it some time for the theorists who have other points of view to come up with explanations," said James Symons, director of the Berkeley lab's Nuclear Sciences Division. "Really the most exciting result might be if it isn't the quark-gluon plasma and it's something else."