Research Magazine 2006

Physics group contributes to landmark quark discovery

Table of elementary particles

A team of UT Arlington physicists participated in the recently announced discovery of a new heavy particle that has three quarks—one from each of the three quark families.

Team members Jaehoon Yu, Andrew White, Kaushik De,  Andrew Brandt, Mark Sosebee, Jia Lie and Armen Vartapetian worked on the Fermi National Accelerator Laboratory experiment called DZero. Several postdoctoral researchers and graduate students assisted.

A Star Wars comparison helps explain the finding. In a scene from the first movie, Jedi Master Obi-Wan Kenobi teaches young Luke Skywalker about the Force.

“It is an energy field created by all living things,” he instructs the lad. “It surrounds us, penetrates us and binds the galaxy together.”

That was probably all Luke needed to know.

But the study of force is a bit more complex, says Dr. Yu.

Luke might have been surprised to learn that there are actually four forces: the gravitational force, between all objects with mass like the sun and Earth; the electromagnetic force, between all objects with electrical charge and magnetism; the weak force, as in nuclear decays (a physics term for diminishing or disintegrating by radioactive decomposition); and the strong force, which binds the nucleus of the atom.

“We have been studying gravitational force for a long time, and thus the force is rather well-understood. And electromagnetic force has been studied for 200 years,” said Yu, a physics associate professor.  “But nuclear power, especially the strong force, has been around less than a century, so there is still much we do not know.”

A brief physics review: Matter is composed of molecules that contain atoms with a nucleus of baryons, protons and neutrons made up of quarks, the fundamental building blocks of matter.

“We had seen particles with quarks from two families,” Yu said. “We had never seen three.”

The particle’s discovery and the measurement of its mass provide new understanding of how the strong force acts on quarks.

“Knowing the mass of the ‘cascade b’ baryon gives scientists information they need in order to develop accurate models of how individual quarks are bound together into larger particles such as protons and neutrons,” Robin Staffin, associate director for high energy physics in the Department of Energy’s Office of Science, said in a news release from the agency.

The significance may be lost on those uninitiated in high energy physics, but Yu says the discovery will give scientists an additional clue in understanding the strong force. High energy physics focuses on the fundamental constituents of matter and the principles that govern their interaction.

“The more we know about the interactions of the quarks, the safer we will be in using nuclear power,” he said.

— Sue Stevens