Lab Beams With a Winning Idea

Scientists at Virginia facility use Nobel-honored research to delve into a mystery of matter

In a lab 25 feet below the ground here, electrons run at close to light speed around a 4,600-foot racetrack.

Focused into a beam the size of a human hair, they slam into an atomic nucleus, sending particles flying and giving scientists clues to what binds the atomic nucleus together.

Using the electron beam, scientists at the Thomas Jefferson National Accelerator Facility are taking the research that captured this year's Nobel Prize in Physics and using it as a springboard to new insights into how the universe is constructed.

On Oct. 5, David Gross from the University of California at Santa Barbara, Frank Wilczek of the Massachusetts Institute of Technology in Boston and David Politzer from California Institute of Technology in Pasadena the won the Nobel Prize in Physics for their explanation of how quarks, the fundamental particles of matter, interact.

'It's why we exist'

"Their theory goes to the very heart of understanding the origin of the matter that we see in the universe," said Tony Thomas, a Jefferson Lab scientist and friend of the prize winners. "It's why we have mass, it's why we exist."

The why-we-exist question has classically been a debate for philosophers. Now, particle physicists are searching for the solid evidence underneath our existence.

All matter is built of atoms. Protons and neutrons form the nucleus of each atom, with quarks as the building blocks for the protons and neutrons.

For every quark there is a complementary "antiquark," which are examples of antimatter. The antiquark displays the opposite characteristics of its quark, such as spin and charge, so adding them should always equal zero.

Scientist assign each quark with the quirky and arbitrary traits of "flavor" and "color." Quarks flavors are "up," "down," "strange," "charm," "top" and "bottom." And a quark can be "red," "blue" or "green."

The closer, the stronger

Up and down, the two lightest quarks, form the majority of matter on Earth.

Quarks are held together by what scientists call the strong force. Gluons, because they "glue" the quarks together, carry the strong force between them.

Thomas and his colleagues want to know what makes the boundaries between protons and neutrons in an atomic nucleus. They are interested how, in real matter, the quarks in a proton and the quarks in a neutron interact.

"Suppose we put several [protons and neutrons] near each other to make a nucleus. The structure of each may be affected because another one is nearby," Thomas said. "They are going to be bumping into one another, and so the structure of the proton may actually change."

"The nucleus is a continuously boiling cauldron of quarks and antiquarks," said David S. Armstrong, an associate professor of physics at the College of William and Mary.

In most cases, the force between two objects gets stronger as the objects get closer, as with magnets.

However, as quarks are pulled apart, the amount of energy used to keep them apart increases. At a critical point, the energy is so great that a quark and antiquark will spontaneously come into existence. Therefore, no quark can ever be alone.

Similarly, if a quark and antiquark are pushed together, energy is produced.

Quarks only account for a minute amount of a proton. One of the largest mysteries is that 99 percent of any matter — a table, a tree, you and me — is not made of quarks. Thomas hopes that by understanding how quarks cooperate within a nucleus, he will be able to find the missing matter.

Matter only has up and down quarks

Another question troubling physicists is why all known matter contains only up and down quarks. What happens if one of the four other types of quarks is put into normal matter?

Armstrong is using the electron beam at Jefferson Lab to discover what happens when a quark of the strange flavor is placed into the mix.

"The main purpose is to try to make a connection between the properties and behaviors of particles around us and those observed in the lab," Armstrong said. "We are using a series of precise experiments that look for the subtle effect that can only arise if strange-antistrange quarks are present."

Strange is the next-lightest of the quarks, and it takes the least energy to create.

Like Thomas' research, Armstrong expects that what he learns will lead to a greater understanding of how quarks associate in the nucleus.

Thomas hopes that his research may someday illuminate areas outside of particle physics.

"The way I look at it, there is a ... constant [number] which is the strength of how a quark interacts with a gluon," he said. "If we could just find a way to change that a little bit, we'd all weigh a lot less.

"There's hope in there for Weight Watchers."