Thursday, February 10, 2000
The finding, still hotly contested, would be the first experimental proof that such a state could exist and could eventually help explain how the stars and galaxies that make up the universe were formed.
But many physicists who have been searching for such proof remained skeptical of the announcement and said they did not believe there was adequate evidence 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 what physicists metaphorically describe as "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 aren't strong enough to predict clear, unambiguous signals, the physicists say.
"There's no smoking gun," said Barry Barish, a particle physicist at Caltech.
What's more, with hundreds to thousands of particles streaming out of these collisions, it's extremely difficult to sort out the signals from the noise.
"It's 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, used a common description among physicists to equate 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.
James Nagle, a Columbia University physicist who will conduct experiments at Brookhaven, said, "If you really want to study something, you don't want to be at the edge. We're going to make a large volume of hot plasma and really study it."
Today's announcement, said one physicist, was being made so CERN could "stake its claim" to finding the plasma, although 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.
"They have seen phenomena that are new, but they have not made a direct observation," he said. "The signals could be stronger, and CERN has not seen them."
Physicists at Brookhaven are preparing to create spectacular collisions in their 2 1/2-mile-long underground ion collider.
The first collisions are expected to take place this summer, and scientific results--including direct observations of a quark-gluon plasma--could be announced in the fall or next winter, Ludlam said.
"We'll be able to
deconstruct quarks and look at how they behave," he said.
"This is probably as close as we're going to get to the beginning
of the universe."
There is one Universe.
It is perpetual, in equilibrium;
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