An electrically neutral lepton of spin 1/2 and extremely low mass that interacts only via the weak force and gravity and as a consequence can typically pass unimpeded through ordinary matter. A common popular illustration of this is that a burst of neutrinos could pass through a light year's thickness of lead and still retain better than two thirds of its strength. There are three known varieties in conventional matter, one in each generation of particles, associated with electron, muon, and tau leptons.
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Development Notes
Text by M. Alan Kazlev; additions by Adam Getchell

Initially published on 09 December 2001.

Significant revisions 23 February 2013.