One neutrino at a time

Physicists in Japan this week announced a big step toward confirming a major physics discovery after a water-filled detector at Kamioka intercepted its first neutrino. The neutrino was fired from a particle accelerator 250 kilometers away. Known as the Long Baseline Neutrino Oscillation Experiment, the project is designed to verify last year's discovery at the Super Kamiokanda detector that neutrinos - particles that rarely interact with other matter - change their type as they travel and thus have mass (see story 9/10/98).

Confirmation that neutrinos have mass, the team says, would have a significant effect on efforts to understand how the universe will evolve and would bolster "Grand Unification" theories. These hold that the four forces of nature - electromagnetism, gravity, the weak nuclear force, and the strong nuclear force - are low-energy remnants of what once was a single force during the universe's earliest moments. By comparing the type and number of neutrinos leaving a lab in Tsukuba City with the type and number arriving at Super K, scientists hope to provide a more rigorous test of last year's results. The international project is the first such experiment to start operation among several proposed or under development worldwide.

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