Researchers at Jefferson Lab hope to better understand the tiniest known bits of matter by playing a subatomic pool game.
Equipment for the experiment will be installed at the Thomas Jefferson National Accelerator Facility this month, and researchers will begin studying the role of "strange quarks" in forming protons next year.
Scientists think that quarks are the building blocks of atoms, joining to form protons and neutrons. Those particles, in turn, form just about everything else, from the sun to toaster ovens. Researchers began predicting the existence of quarks in the early 1960s. By 1995, six types of quarks had been found: up, down, strange, charm, bottom and top. The difference between each is based mostly on their electric charge and mass, with the lightest — up and down — weighing in at 200 times less than a proton. The heaviest — top — is almost as bulky as a full proton.
Jefferson Lab scientists will have to use a physics trick shot to get an idea about the internal structure of protons.
Researchers think that the strange quark is in a "sea" of quarks in the outer region of the proton, as opposed to the interior of the proton, where three heavier quarks form a nucleus.
The process shoots an electron at a proton. The electron will interact with the quarks in the proton, causing the proton to ricochet at a certain angle. It's something like the way that the properties and position of a pool ball help determine what happens when it's struck by a cue ball.
Consequently, by using mathematical models to retrace the proton's path, scientists can learn what kind of energy the quarks must have had to produce a particular effect.
"It's like zooming inside the proton," said Julie Roche, a post-doctoral student at the College of William and Mary who came to the lab two years ago from France to work on the experiment. "We know that they are in there, we just don't know where they are."
Certainly, the work won't lead to a cure for cancer or a nifty new gadget, but that doesn't make the research any less important, said Allison Lung, project manager. The simple fact is that quarks make up almost everything in the universe. And scientists know almost nothing about them.
"It's basic knowledge you need to understand your place in the world," she said. "It's important because it relates directly to the genesis of the universe."
Before 1964, though, quarks were a quack.
Until recently, scientists thought that most matter was a combination of just the up and down quarks.
But then, researchers got better instruments, which provided more information.
That meant that researchers have had to reassess their theories, and experiments like the G-Zero effort have been started.
The Jefferson Lab experiment will try to learn more about strange quarks because their lack of mass makes them the most likely to form during collisions.
The G-Zero experiment will be looking for strange quarks specifically, shooting electrons at nearly the speed of light into a cylinder of cold liquid hydrogen. It will take about 70 trillion collisions over about seven months to get enough data.
G-Zero is one of two strange-quark experiments being done at the research lab. Few such studies are being done elsewhere in the world. There's an experiment at MIT-Bates Laboratory at the Massachusetts Institute of Technology and one at Mainz laboratory in Germany.
Even among those tests, though, the G-Zero experiment is unique.
Three things set it apart: technology, staff and ability.
G-Zero has meant building new equipment for Jefferson Lab, a $7 million investment during the next four years. The only things that the existing lab will provide are the accelerated electrons. The equipment — from the $2 million superconducting magnet used to steer the particles to the tools used to detect the particles — are all being crafted elsewhere and brought in. The work is being financed by grants from the National Science Foundation and the U.S. Energy Department.
It's a consortium for the lab with international collaborators. Scientists from France and Canada are building the equipment and providing expertise. Nuclear-physics experiments typically involve only 20 or 40 researchers, but more than 100 scientists and about a dozen doctoral students will be involved with G-Zero.
The other experiments can measure only one of two aspects of the quarks, called form factors. It boils down to understanding where the particles are and how much energy they have, but scientists could examine only one or the other because of existing technologies.
Jefferson Lab's instruments will allow scientists to look at both aspects, providing greater insight into the nuts and bolts of reality.
"Protons are everywhere around us," Roche said. "We just don't know how they work."
— Michael Hines can be reached at 247-4760 or by e-mail at firstname.lastname@example.org
Submitted: Sunday, September 30, 2001 - 12:00am