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Physicists claim proof of new state of matter

Thursday, February 10, 2000



A coalition of nuclear physicists is announcing today that it has gathered evidence for the existence of an entirely new state of matter - one that may have arisen in the first split seconds after the big bang.

The finding, still hotly contested, would be the first experimental proof that such a high-energy state could exist and could eventually help explain how the stars and galaxies that make up the universe were formed.

But many physicists remained skeptical and said they did not believe there was adequate proof that the new state of matter had actually been created in the lab. Others suggested that the announcement was a political move, made by a European laboratory with aging machinery that will soon be eclipsed by a bigger and better machine being built in the United States.

The evidence centers on intriguing particles called quarks, which are considered to be the basic building blocks of matter and were first detected in 1974. Most atomic particles, like neutrons and protons, are made up of quarks, and it was long believed that it would be impossible to find a "free" quark.

All quarks are tightly bound together in "bags," in which they rattle around like loose marbles. Except at energies rivaling the big bang itself, the quarks can never escape the clutches of the gluons that trap the quarks inside the bag.

But theorists describing the state of the forming universe say that at extremely high temperatures, quarks would have been free-floating in a "quark-gluon plasma." This plasma is thought to be the origin of all matter in the universe.

For 15 years, physicists from around the world have been working with a particle accelerator at CERN, the European Laboratory for Particle Physics, in Switzerland, smashing high-energy beams of lead ions into targets.

The collisions create temperatures more than 100,000 times hotter than the interior of the sun and very high-energy density states that may mimic the conditions of the forming universe. The goal has been to create - and detect - a quark-gluon plasma.

Today scientists meeting in Switzerland are announcing that they believe several years of their experiments do provide evidence for this plasma. The announcement is somewhat unusual, because it is not based on one new experiment but on an accumulation of suggestive evidence gathered over several years.

Several physicists not directly involved in the experiment were skeptical, if only because no one knows exactly what a quark-gluon "soup" looks like. That makes it almost impossible to say for certain whether the soup has been seen. The theories simply arenít strong enough to predict clear, unambiguous signals, the physicists say.

"Thereís no smoking gun," said Barry Barish, a particle physicist at California Institute of Technology.

Whatís more, with hundreds to thousands of particles streaming out of these collisions, itís extremely difficult to sort out the signals from the noise.

"Itís a real mess experimentally," said Stanley Wojcicki, particle physicist at the Stanford Linear Accelerator Laboratory.

Lee Schroeder, director of the nuclear physics division at the Lawrence Berkeley Laboratory, equated the process with slamming two Swiss watches together and then trying to recreate the originals from the mess created in their wake.

Others said the only way to determine that the plasma existed would be with direct observation - for example, the measurement of gamma rays given off by the fleeting quarks.

Such evidence is expected to be gathered by a new particle accelerator, called a relativistic heavy ion collider, recently constructed at the Brookhaven National Laboratory on Long Island, N.Y., that will generate even more spectacular collisions and higher-energy densities than the one at CERN.

Todayís announcement, said one physicist, was being made so CERN could "stake its claim" to finding the plasma, even though it did not have adequate proof to do so. "The Brookhaven machine is breathing down their neck," he said.

Thomas Ludlam, a nuclear physicist at Brookhaven who is overseeing the experiments that will be conducted on the new machine, said the CERN work is an important step toward detecting the plasma but that more experimental evidence is needed.

©2000 THE PLAIN DEALER. Used with permission.


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