The numbers are impressive: 550 scientists at 73 institutions in nine countries combing through millions of bits of data for 16 months. And the goal is, well, cosmic: to make a precise measurement that might help us understand how we and everything we see and touch came to be.
When the value--0.34±0.20--popped up simultaneously on three computer screens at the Stanford Linear Accelerator Center in January, particle physicists hailed it as a wondrous "baby step" toward a new understanding of the universe.
"The excitement is that the idea works and the experiment works--we have 'first results,'" says researcher Pat Burchat. "We have demonstrated the feasibility of the experimental approach and are on our way."
Burchat, a Stanford physics professor, and her colleagues from around the world have been working for a decade to design, build and run an experiment that will help explain why there's more matter than antimatter in the universe--a fundamental question of particle physics. (Though it's often glorified in science fiction, antimatter is very real--a mirror image of matter that has opposite electric and magnetic properties.)
The researchers use SLAC's high-energy BaBar facility to produce collisions between electrons and their antimatter counterparts, positrons, then compare the rates at which they decay. Another team known as the BELLE collaboration has been pursuing a similar experiment at Japan's high-energy physics facility, KEK.
So far, the numerical value the BaBar collaborators have measured--known as sin 2b--is consistent with the Standard Model of physics, the prevailing theory explaining how matter and energy interact. Although the result is the most precise to date, it's still not refined enough that physicists are willing to make any definitive statements. They're not even calling it a discovery--yet.
"We don't know what more precision will bring us," says Burchat, PhD '86. "Perhaps the Standard Model will once again hold up. Or perhaps we'll observe some inconsistencies that could point the way in our quest to understand what physics lies beyond the Standard Model."
Achieving greater precision will take time: the experiment is expected to last another five to 10 years. During 1999 and 2000, BaBar produced a whopping 25 million particle collisions. But by 2002, researchers expect it to churn out 80 million collisions per year. "It's not like an undergraduate lab, where you want to get the 'right' answer," Burchat says. "Instead, we want to know what nature has given us. It's a monumental effort, inspired by the desire to understand a question as basic as: how is matter different from antimatter?'"
For the past 18 months, BaBar collaborators have worked in round-the-clock shifts to test and retest what project spokesperson Stewart SMITh calls "the number from hell." Every day from 8 a.m. to 10 a.m., teams of researchers confer through videoconferences from their offices in Canada, China, France, Germany, Great Britain, Italy, Norway, Russia and the United States. During the past year, Burchat coordinated the analysis portion of the experiment.
After pursuing a more precise sin 2b for more than a decade, however, Burchat missed the moment of revelation. The date for publicly releasing the results kept shifting, and Burchat and her husband, Tony Norcia, PhD '81, had promised to take their children, Matthew, 12, and Michael, 9, to a Tahoe ski resort. At the moment computers flashed the final computation in a crowded office at SLAC, Burchat was on the road home from the mountains. Fifteen minutes later, she stopped at a restaurant in Davis and called her colleagues from a pay phone.
Regrets? "Not enough to not go skiing with my family."
