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Number 631 #1, April 2, 2003 by Phil Schewe, James Riordon, and Ben Stein

The First-Ever Large China-Taiwan Scientific Collaboration

The first-ever large China-Taiwan scientific collaboration has carried out a reactor experiment which puts a new upper limit on the neutrino magnetic moment. Consider first the electron; it not only has electrical charge but also spin, which means that it will act like a tiny magnet. Even a neutral atom, because of its internal distribution of negative and positive charge, can have a nonzero magnetic moment. Consequently neutral atoms can be controlled, to some extent, by magnetic fields. But what about a neutrino? Neutrinos may well possess a small amount of mass, But what about magnetism? Can they effectively have a tiny bit of charge or internal structure? A nonzero neutrino magnetic moment provides the neutrino with a way to interact electromagnetically with the world; generally the neutrino is thought to interact only via the weak nuclear force. Evidence for nonzero magnetic moment would show up in several ways: in anomalous electron-neutrino scattering, in radiative decays in which the neutrino casts off a gamma ray, and in various astronomical settings, such as supernovas. The TEXONO collaboration, using neutrinos from the 2.9-GW Kuo-Sheng Nuclear Power Station in Taiwan, looked for a characteristic anomalous electron energy spectrum arising from electron-neutrino scattering. They did not see any such evidence, and from this they derive the best direct-laboratory upper limit on neutrino magnetic moment, 1.3 x 10-10 times the magnetic moment of the electron (a unit also known as the Bohr magneton). The team also derives an indirect bound on
neutrino radiative decays. (Li et al., Physical Review Letters, 4 April 2003; contact Henry Wong, Academia Sinica, Taiwan, 886-2-2789-6789) The TEXONO Collaboration is supported by several research institutions and their respective funding agencies from Taiwan and China. An efficient flow of students and scientists moves in both directions.

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