Neutrinos

What are they?

Neutrinos are members of the Standard Model, belonging to a class of particles called leptons. For a long time scientists believed neutrinos were massless and moved at the speed of light. However, physicists have found increasing evidence that these tiny particles in fact have mass, although one much less than that of the electron. Right now we only know the upper limits on what the mass could be and the mass differences between flavors of neutrinos, although there are many current experiments designed to probe this question. The difficulty lies in the fact that neutrinos are extremely non-interacting and therefore troublesome to detect. Scientists know with certainty that they are chargeless and have a spin angular momentum of 1/2. Every measurement made of the elements of the standard model (including neutrinos) has shown that they have no internal structure; indeed, that is why they are called fundamental particles. In addition, neutrinos seem to be stable.