New Model Of Atomic Forces May Help Explain Proton Structure

April 22, 1998

COLUMBUS, Ohio -- Researchers at Ohio State University have developed a new model of atomic forces that may solve a long-standing problem in particle physics.

The work may aid the understanding of the structure of protons and other particles that contain quarks because it begins to reconcile physicist Richard Feynman’s 1970s model of the proton with modern views of the quark structure of sub-atomic particles.

“We’re hoping our work will make it easier for people who work with the quark model to calculate a lot of experimental information,” said Kenneth Wilson, professor of physics at Ohio State and 1982 Nobel Laureate in Physics. “Right now, the equations that describe proton structure are very complicated.”

Wilson helps to lead the research group for this project, which includes Robert Perry, also professor of physics, and Stan Glazek, a frequent visitor to Ohio State and associate professor of physics from Warsaw University. The researchers discussed their model April 18 at the 1998 American Physical Society meeting in Columbus.

Physicists have a hard time mathematically describing the structure of the proton, because the particle is supposed to be surrounded by a cloud of virtual particles that blink in and out of existence all the time, severely complicating the equations.

In the early 1970s, Feynman, a former physicist at Caltech, devised a way for physicists to separate the proton’s constituents from these virtual particles -- mathematically, at least. He suggested that a proton moving at the speed of light could outrun the slower virtual particles so physicists could observe its constituents on their own. He envisaged the proton’s constituents as being just three fundamental particles called quarks. This greatly simplified the mathematics.

Physicists now hypothesize that protons are made up of quarks and other fundamental particles called gluons, and that the massless and neutrally charged gluons bind quarks together.

The current theory is much more complicated than Feynman’s: The connection between quarks and gluons is supposed to be so strong that smashing a proton in a particle accelerator would release not just three quarks as Feynman predicted, but a shower of quarks, anti-quarks, and gluons.

Still, Feynman’s ideas provided for simple equations that matched experimental results concerning the energy states of protons.

“The question was, once we had this very complex quark theory, why did Feynman’s simple model still work so well? No one has ever been able to figure out why. In fact, the problem became so difficult that people just gave up,” said Wilson.

Wilson and his colleagues have formulated a new picture of quark-gluon interaction. They think that gluons may bind strongly to each other but not so strongly to quarks. That would prevent quarks from escaping easily during experiments, but also allow for Feynman’s simpler mathematical model.

“The coupling of gluons to each other is quite strong, and that coupling confines quarks inside the proton,” explained Wilson.

With this theory, when the bonds between gluons are broken, the reaction emits mostly other gluons. Extra particles such as anti-quarks and virtual particles don’t emerge because no strong bonds exist between quarks. Even gluons should be rarely emitted because, in the new theory, they are expected to have high masses, making them hard to produce.

This work, which was sponsored by a grant from the National Science Foundation, is in the preliminary stages, and the Ohio State researchers will continue to develop it mathematically. But even before then, they hope other physicists will explore the new theory as well.Written by Pam Frost, (614) 292-9475;

Ohio State University

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