First data from new neutrino detector.Nuclear fusion reactions in the sun's core produce huge quantities of neutrinos, elusive subatomic particles that interact only weakly with ordinary matter. Japan's new Super-Kamiokande neutrino detector A neutrino detector is a device designed to detect neutrinos. Because neutrinos are very weakly interacting, neutrino detectors must be very large in order to detect a significant number of neutrinos. has been monitoring the sun's output since April 1996 (SN: 9/7/96, p. 149), and researchers have analyzed the first 102 days of data. Preliminary results confirm previous experimental findings that the number of solar neutrinos detected on Earth falls significantly short of the number predicted by conventional theory (SN: 12/21&28/91, p. 406). The data also contain tantalizing tan·ta·lize tr.v. tan·ta·lized, tan·ta·liz·ing, tan·ta·liz·es To excite (another) by exposing something desirable while keeping it out of reach. hints that more neutrinos are detected at night than during the day and that they appear more plentiful during certain times of the year, says Kenneth K. Young of the University of Washington in Seattle, who is a member of the Super-Kamiokande collaboration. The standard model of particle physics particle physics or high-energy physics Study of the fundamental subatomic particles, including both matter (and antimatter) and the carrier particles of the fundamental interactions as described by quantum field theory. posits that neutrinos come in three varieties: the electron, muon muon (my  `ŏn), elementary particle heavier than an electron but lighter than other particles having nonzero rest mass. , and tau neutrino tau neutrinon. A probably stable elementary particle in the lepton family having a mass less than 60 times that of the electron and no charge. See Table at subatomic particle. . Super-Kamiokande detects just electron neutrinos. One possible explanation for the shortfall is that neutrinos may change back and forth between the detectable variety and one that isn't. This oscillation process may also occur more readily when neutrinos pass through Earth, possibly creating a difference between night and day neutrino neutrino (n trē`nō) [Ital.,=little neutral (particle)], elementary particle with no electric charge and a very small mass emitted during the decay of certain other particles. detection rates. The seasonal fluctuations may depend on the distance between the sun and Earth, which varies by about 5 percent during the year. At least another year of results from Super-Kamiokande is needed to establish the difference, if any, between the day and night rates, Young says. |
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