Courtesy of University of Hawaii
University of Hawaii physics professor John Learned,
standing, wtih UH assistans physicist Shigenobu Matsuno, right,
and graduate student Dean Takemori, display a photomultiplier
light detector, used to help provide evidence that neutrinos
oscillate and thus have mass.

---

UH scientists take
part in breakthrough
physics discovery

Neutrinos have mass,
a Japanese-American
research team concludes

By Helen Altonn
Star-Bulletin

A Japanese-American team with key Hawaii members today announced a discovery hailed as the greatest of this decade, perhaps even this century, in elementary particle physics.

The findings rattle the standard theory of particle physics and move scientists a notch forward in understanding the universe.

Data from a $100 million detector, Super-Kamiokande, beneath the Japanese Alps, show that neutrinos raining on Earth from cosmic rays have mass, the group said.

This means neutrinos are elementary particles that have the smallest mass but collectively may account for much of the mass of the universe.

The different types or "flavors" of neutrinos oscillate or change identities back and forth as they travel through space, the scientists said. That can occur only if a neutrino has mass, they said.

While the neutrino mass is the smallest observed yet for elementary particles, it is "still sufficient that the relic neutrinos made in staggering numbers at the time of the Big Bang account for much of the universe," the group said.

The discovery was announced at "Neutrino '98," an international physics conference in Takayama, Japan.

Theoretical models now must be altered, said University of Hawaii physicist John Learned, a leader in the U.S.-Japan effort.

"These new results could prove to be the key to finding the holy grail of physics, the unified theory," he said.

Scientists knew "other fundamental building blocks of the universe all had some mass, that is to say, quarks and leptons, things of which atoms are made," Learned said. However, neutrino mass was considered "absolutely zero."

"What we have in this situation with neutrinos is something we don't see anywhere else in the universe. As with people, we know them by their interactions . . .

"For every chunk of ordinary matter there is a well-defined and unique mass," he said.

But with a neutrino, "It's kind of a Dr. Jekyll and Mr. Hyde sort of an affair. If you look at it in different moments, it behaves in different ways. All other particles that we know have the same mass and interact the same way at all times."

Super-Kamiokande scientists for two years have been studying neutrinos captured in a 50,000-ton tank of highly purified water about 3,300 feet underground.

Neutrino interactions giving off faint flashes of light are detected by more than 13,000 photomultiplier tubes.

Learned, who has studied neutrinos for more than 20 years, calls some of the findings "very peculiar stuff." For instance, there are three types or "flavors" of neutrinos -- electron, muon and tau.

And muon neutrinos are oscillating between at least two different neutrino flavors -- possibly the tao neutrino, he said. "Or it could be there's a new sterile neutrino involved."

It is suggested that one or all three types of neutrinos could be oscillating from our universe to a parallel or mirror universe and back again, Learned said.

"Thus, neutrinos would be our only way to communicate with the other universe. . . . It could be that this parallel galaxy is sitting right on top of our galaxy. That would account for some dark matter."

But a simpler solution, he said, is the tao neutrino is the muon neutrino's oscillating partner. "That would be my first bet."

Learned was one of seven people who formed the IMB (Irvine-Michigan-Brookhaven) detector in a mine under Lake Erie in Cleveland in the 1980s.

Neutrino detectors built in Cleveland and later in Utah and Japan were designed at a workshop at UH in 1976, Learned said.

The IMB group merged with the Japan scientists in 1994 in a move initiated by UH graduate Steven T. Dye, then a Boston University researcher, now associate dean at Hawaii Pacific University.

Other UH physicists with the Japan project are analysis group leader Shigenobu Matsuno and Victor J. Stenger. Also involved are graduate students Atsuko Kibayashi and Dean Takemori.

UH graduate John Flanagan, now at Japan's KEK laboratory, wrote the first dissertation on Super-Kamiokande with evidence for neutrino oscillations, Learned said. Robert Svoboda, former UH graduate teaching at Louisiana State University, is a Super-Kamiokande analysis group leader.

Also studying neutrinos in the UH elementary particle theory group are professors Sandip Pakvasa, Xerxes Tata and Walter Simmons.