Nature rarely allows easy insight into fundamental processes. But a recent Jefferson Laboratory experiment involving more than 75 researchers from the United States and abroad ran smoothly, without serious incident or disruption. And its pending findings could prove among the decade's most important in the field of low-energy nuclear physics.

Preliminary results from the Hall A Proton Parity Experiment, or HAPPEX, were announced at a mid-July seminar held at Jefferson Laboratory. The initial conclusion: Strange quarks, the third lightest of the six so-called "flavors", or varieties, of the qu ark family of basic particles, are surprisingly scarce in ordinary nuclear matter.

"The crucial thing in a frontier science is to understand the lay of the land," says Paul Souder, co-spokesperson for the international HAPPEX science team and a professor of physics at Syracuse University. "This is a very important step ...a significant advance."

Another HAPPEX co-spokesperson and William and Mary physics professor, John Michael Finn, says the experimental outcome should enlarge physicists' understanding of proton structure, eventually leading to a more complete understanding of what literally hol ds the nuclear world together.

"Dynamic quark interactions within the nucleus account for almost the entire observed mass of the visible universe," Finn points out. "What we have here is a technique for measuring specific quark distributions in the nuclei. We can determine how much s trange quarks contribute to this net distribution."

One of the key motivations for HAPPEX was to shed light on the "proton spin crisis". Research over the last decade has shown that the "spin" of the proton, responsible for its magnetism and thus for such technologies as medical Magnetic Resonance Imagin g, is not carried by its basic three "valence" quarks (the two lightest "up" and "down" quarks). To investigate the missing spin problem, HAPPEX makes us of a subtle property of subatomic forces.

Most forces in nature act the same way in our world as in a "mirror world" where right-handedness. One of the subatomic forces, the "weak interaction" does not obey this symmetry principle which is called parity. HAPPEX exploits this violation to probe the way in which different flavors of quarks assemble themselves into the protons and neutrons that comprise the atomic nucleus. In particular, HAPPEX is sensitive to matter/antimatter pairs of "strange" quarks that spontaneously appear and disappear wit hin the nucleus. These "sea" quarks exist in addition to the three "valence" quarks that are the basic components that make protons and neutrons.

"We have this model of a three-quark proton. It's not right," contends Charles K. Sinclair, injector group leader for Jefferson Laboratory's Accelerator Division. "The angular momentum doesn't add up. The Hall A experiments were probing the very detail s of the proton's structure. It's hot stuff."

Historically, parity experiments have been difficult to arrange and conduct. Physicist Souder had initially proposed a HAPPEX-like experiment as early as 1980, but was stymied by cost and lack of appropriate apparatus.

Once Jefferson Lab's accelerator was developed, however, it became that the necessary equipment would be available to researchers at reasonable expense. Request for HAPPEX funding was made in 1991 and the project was approved by the end of the 1992 calen dar year.

Proof-of-concept testing for HAPPEX began in August 1997, with a full-scale dress rehearsal conducted in December of that same year. By the end of the first quarter of 1998 the HAPPEX science team began its work in earnest.

"They ran the experiment in April and announced the results in July. We're not talking years; we're talking months," Sinclair says. "If you can bring out experiments every few months you really make progress. You've opened up new doors."

Co-spokespersons Finn and Souder say that from a purely technical point of view, HAPPEX was a stunning achievement. They credit a large part of the HAPPEX project's success to the quality of the Lab's electron accelerator which, like a powerful microscop e, is capable of unprecedented resolution. The electron beam was extraordinarily stable as well, eliminating certain kinds of interference that could otherwise affect the validity of experimental data.

In particular, Finn attributes the positive outcome to the collective experience accumulated by the primary researchers and the expertise of Jefferson Lab personnel.

"If you want to be successful you have to work with people who know what they're doing," Finn explains. "This is not the kind of experiment where you do on-the-job training. And the [electron] beam was absolutely outstanding. The machine was spectacula r, it was extremely quiet."

Funding is being sought for a follow-p experiment that would run at even higher resolution by spring 1999. Although it is difficult to predict what, if any, applied-science benefits might result from the HAPPEX investigations, Finn believes that they wil l come in time.

"What we've seen historically is that any advance in the fundamental understanding of nature has led to significant technological advances," he says. "In the case of electromagnetism, it took nearly half a century. It's a long-term, complex process.

"The full benefits from the kind of knowledge we're talking about may take a century or more to develop. How that knowledge will be used to benefit mankind isn't yet known. That they will be benefit mankind is highly likely - inevitable, in fact."

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