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The Future of Neutrino Research

In Lead, South Dakota, population 3,500, a banner hangs at City Hall proclaiming February 23, 2001, as Neutrino Day. Physicists, as Dr. Kenneth Lande will attest, get treated very well around here. Mining operations at the Homestake gold mine, where solar neutrinos were first detected, will end this year, but Lande, a Penn physics professor, is part of an effort to convert the space into the Homestake National Underground Science Laboratory, which would be the “premier world location for underground science.” Its organizers are seeking $281 million from the National Science Foundation. “Every death is followed by a birth,” says Lande, speaking from 4,850 feet below the ground, where he’s “trying to organize the transition from mine to lab.” He says 35 “letters of interest” have already come in from physics, biology, and geology researchers who want to use the lab in a variety of experiments, some involving neutrinos. He expects Penn to play a major role in the facility.
    In the meantime, scientists at the Sudbury Neutrino Observatory (SNO) will continue refining their understanding of how neutrinos transform from one type to another. After SNO, other questions remain to be answered about these particles: What are their masses? Does another hidden “flavor” exist? According to Lande, there may be a fourth type of “sterile” neutrinos, which don’t engage in the kinds of reactions the others do.
    Another possibility the next generation of experiments will examine, says Lande, is whether there are variations in neutrino signals depending on the time of day or night, or as a function of the seasons. During the day an underground detector is separated from the sun’s output of neutrinos by a mile or so of Earth. At night, there would be 8,000 miles between Earth and the sun’s output. “What’s the effect on neutrinos as they go through the Earth? Are there some more neutrino flavor changes as they pass through Earth?”
    Beyond those inquiries, Lande says, now the neutrino can be used to probe the center of the sun and find out whether it varies its behavior over time. The neutrino can also be used as a probe to see inside a supernova formed when a star collapses: “Because some exciting things happen there in a very short period of time.”

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