Now researchers at the Brookhaven National Laboratory on New York's Long Island are getting ready for an experiment that will try to create in the laboratory a sort of post-bang plasma. They'll be looking for it in the aftermath of violent collisions between gold nuclei traveling in opposite directions at nearly the speed of light.
After eight years of construction and at a cost about $600 million, a new particle accelerator called the Relativistic Heavy Ion Collider, or RHIC, is nearly ready for operation. Scientists at Brookhaven have tested the 2.4-mile two-lane particle racetrack, and found it to be working beautifully, said Tom Ludlam, associate project director for the RHIC experiment.
Inside the underground circular track, team scientists successfully brought beams of gold ions up to 99.99% the speed of light, and detected the beams with the accelerator's four precision detectors. The successful trial prompted the Department of Energy last week to declare the facility operational.
While most particle accelerators crash protons or electrons together to see what happens, scientists at the Brookhaven collider have chosen to annihilate much heavier lumps of substance. Protons are the positively-charged building blocks of atomic nuclei, while electrons are the negatively charged particles that swirl around them. Gold ions, which are atoms of gold that have been stripped of their orbiting electrons, contain 79 protons. They are the heaviest particles to become the target of annihilation researchers.
"We start with two atomic nuclei which collide. We then expect to see tens of thousands of elementary particles produced -- a sort of mini-bang," Ludlam said,. "It's almost like looking at a supernova is for astronomers. The only problem is it takes place in a tiny fraction of a second and then it's gone. And then it produces not light, but high-energy elementary particles."
The collision of two heavy nuclei produces so much heat that the ions literally melt into quarks -- the constituent parts that make up atoms -- Ludlam said. In the aftermath of these high-energy collisions, scientists hope to see a new state of matter, something they call quark-gluon plasma, the proto-universal goo scientists think might have existed in the instants just after the big bang.
"By trying to look at these most extreme forms of nuclear matter, we're examining matter as it was in the very early stages of the universe, but we're doing it now by looking inward at the very smallest distant scales of the atomic nucleus rather than looking out at the largest distant scales of the galaxy," Ludlam said.
To create this fundamentally different phase of matter, scientists need a huge accelerator like RHIC. Proton or electron collisions dont produce enough of this matter to meaningfully study, a problem Ludlam compared to the trouble of studying steam by boiling a few molecules of water.
"If you're looking for a phase transition in water its not good enough to have one or two molecules in a pot and watch it boil. You need at least a few drops," he said.
Heavy ion collisions are the few drops of matter that physicists need.
To detect the quark-gluon plasma, scientists are going to measure hundreds of thousands of ion collisions. The RHIC collider produces tiny beams of gold ions, roughly a foot long and about two one-hundreths of an inch (half a millimeter) across. These tiny needle-shaped beams of concentrated gold ions each contain about a billion nuclei, and travel around the accelerator 100,000 times every second.
Ludlam says when the experiment is up and running, about 60 of these beams will be in the accelerator at any given instant, half zooming clockwise, half speeding counterclockwise, each of the beams passing through each other in opposite directions millions of times per second.
Most of the time beams will pass through each other without causing any gold nuclei to directly collide, but the amount of nuclei and the amount of collisions mean that the accelerator will produce about 1,000 direct collisions per second, Ludlam said. The experiment will continue to smash particles together for months.
By analyzing a huge number of collisions, physicists at Brookhaven hope to learn how the quark-gluon plasma behaves and how it forms more complicated forms of matter as it cools.
"It's very much like an astronomical experiment where astronomers look at the whole galaxy of stars, they look at the light that's coming from different types of stars they can find out what the temperature was, they can see how stars evolved by looking at young stars, looking at old stars." Ludlam said. "By looking at the many hundreds of thousands of collisions that we're going to be seeing in this machine with these giant detectors we can do exactly that kind of analysis on the quark-gluon plasma."
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