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Scientists affirm mass of neutrinos, corroborate Japan study.

TOKYO, June 19 Kyodo

An international team of scientists from Canada, Britain and the United States has found ''direct evidence'' proving that tiny subatomic particles called neutrinos have mass, team members said Monday.

The findings on neutrinos, which have so far been shrouded in mystery, were drawn from observations made at the Sudbury Neutrino Observatory (SNO) near Sudbury in eastern Canada.

Neutrinos are produced in vast numbers by the sun and other astrophysical objects due to nuclear fusion within the sun's interior.

Members said the latest results, which study the presence of mass in neutrinos from a different angle, corroborate earlier measurements of the scattering of solar neutrinos from electrons in ordinary water which were made three years ago by a team composed mainly of Japanese scientists.

The first SNO results were detected through the SuperKamiokande detector at the Institute for Cosmic Ray Research of the University of Tokyo in Gifu Prefecture.

These combined data provided direct evidence of the phenomenon that neutrinos oscillate, according to members.

Members said they have arrived at definitive results that electron neutrinos from the sun transform into neutrinos of another type, wherein such a transformation points to direct evidence that neutrinos have mass.

They said that results showed that ''by combining this with information from previous measurements, it is possible to set an upper limit on the sum of the known neutrino masses.''

The SNO, located 2,000 meters under ground in a nickel mine, uses 1,000 tons of heavy water to detect all three types of neutrinos including electron neutrinos.

Construction of the SNO laboratory began in 1990. Measurements at the laboratory began in 1999, a year after its completion.
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Publication:Japan Science Scan
Date:Jun 23, 2001
Words:278
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