Neutrinos are three of the twelve fundamental fermions of the Standard Model. These three particles are usually referred to by their flavor: electron, muon, and tau. These particles were originally thought to be massless, but now we know that neutrinos do in fact have very small masses. Scientists have also realized that the neutrinos' ability to morph from one flavor to another is related to the mass differences between the three particles. The physics governing neutrinos is a fascinating particle physics mystery.
© 2014 PBS & WGBH Educational Foundation. All rights reserved.