Profile in Physics: Charged Up - There's nothing neutral about Boris Kayser

by Gary Ruderman

Boris Kayser's passion runs deep underground. Some of Kayser's strongest scientific interests lie at the bottom of mines where much of the basic research begins on the elusive yet abundant and critically important neutrino.

Last fall, Kayser and other particle physicists descended ("It felt like we were dropped") down a mile-long mine shaft at the old Homestake Gold Mine in Lead, S.D., site of the world's first solar neutrino detector.

"For me," he said, "it was a shrine."

Kayser, 63, is an overtly enthusiastic particle physics theorist whose eyebrows and voice rise in proportion to his excitement. He joined the staff of Fermilab's theoretical physics department in October 2001, with the title of Fermilab distinguished scientist. He brought with him more than a decade of academic research, and three decades at the National Science Foundation (NSF). As Fermilab undertakes its neutrino detection and oscillation experiments with MiniBooNE and MINOS, Kayser hopes for a confrontation with big questions.

"If one wants to understand the universe, one must understand neutrinos," Kayser explained. "If there were no neutrinos, the sun and stars would not shine. There would be no energy from the sun to keep us warm, no atoms more complicated than hydrogen, no carbon, no oxygen, no water, no us."

He summed it up: "No neutrinos-no NU'S-would be very BAD NEWS."

Kayser is most interested in the matter-antimatter relations that neutrinos may challenge.

"In the Standard Model of Particle Physics," he said, "you have a detailed picture of nature. We try to do experiments to verify that this picture is correct. But the Standard Model is surely incomplete, so we're also looking for places where it breaks down. One piece of experimental breakdown is the non-zero mass of neutrinos. The Standard Model assumes that neutrinos have no masses."

Questions abound: Where do neutrinos get their mass? Are there more than three types of neutrinos? Are neutrinos identical to their antiparticles? In a public lecture, Kayser likened neutrino oscillation to ice cream spontaneously changing flavor: the oscillation changes the "flavor" of the neutrino as it travels over a long distance. While the particle is born in the earth's atmosphere as a 'chocolate' or muon neutrino, it can, over a great distance, become a 'strawberry' or tau neutrino.

Kayser has already placed a theoretical wager on Charge-Parity-Time Reversal invariance. If neutrinos have a different mass than their antineutrinos, then CPT invariance is violated. Theorists at Fermilab and elsewhere have suggested that nature does violate CPT in just this way.

Kayser's bet: "This would be a big shocker and I'd bet against it. But nature is full of surprises. It's loads of fun to think what the world would be like if CPT is indeed broken, and it's important to see experimentally whether it's broken or not."

A New Jersey native, Kayser was a Westinghouse Science Talent Search winner in high school before earning an undergraduate degree in physics at Princeton in 1960. For his Ph.D., Kayser chose particle physics at CalTech. In 1972 he joined NSF, where he and several colleagues helped found the NSF-funded Institute for Theoretical Physics at the University of California at Santa Barbara.

While at NSF, Kayser's interest was piqued by the new field of neutral weak currents. His research migrated away from strong interaction physics, toward the neutral, weakly-interacting neutrino. The switch left him-he says-"more charged. I'm intrigued by not knowing the underlying physical laws of this new discipline."

But he felt the classic administration/research bind. He said he was able to author or co-author more than 100 physics papers during his time at NSF only by defying the laws of time: "I spent 100 percent of my time in administration-and the other 100 percent on research."

At Fermilab, he feels he can give his enthusiasms (and his facial and vocal emphasis) free reign- enthusiasms that include another passion, CP Violation beyond quarks and strong interactions. In this area of matter-antimatter asymmetry, Kayser and others see further possibilities for cracking the Standard Model.

"We are lovers of symmetry," he said. "We would expect matter and antimatter to behave in the same way, or in mirror images of behavior, like the equal but opposite charges of electrons and positrons. But nature doesn't work that way; the mirroring is not precise. Otherwise you'd walk down the street, meet the anti-you, and both annihilate.

"Something has to explain the preponderance of matter over antimatter," he continued. "We know that quarks violate symmetry-that was the discovery of CP Violation in k mesons, a very tiny effect. But is this CP Violation the only source? We need something more to explain the matter-antimatter asymmetry, and we're confirming big asymmetries in b mesons, which can be made in the Tevatron. So we want to measure a whole bunch of different decays in b mesons, and others which aren't CP violating but are related. We want to see them all and hope there's a failure, a breakdown in the Standard Model."

A breakdown means the chance to build anew.

"This is very basic stuff," Kayser said. "Recently both CP Violation and the physics of neutrinos have become very exciting because of experimental discoveries. These areas will be pursued big-time at Fermilab-at CDF and DZero, at BTeV, in the neutrino experiments that are coming together and maybe more of them in the future. Nature may not be what we've thought for the last 50 years. Fermilab is the crossroads where this is all happening. I love it."