Neutrino - Wikipedia - lepton number and weak isospin  ## Metadata - Author: **lepton number and weak isospin** - Full Title: Neutrino - Wikipedia - Category: #articles - URL: https://en.wikipedia.org/wiki/Neutrino ## Highlights - A neutrino (/njuːˈtriːnoʊ/ nyoo-TREE-noh; denoted by the Greek letter ν) is a fermion (an elementary particle with spin of 1 / 2 ) that interacts only via the weak interaction and gravity.[2][3] The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The rest mass of the neutrino is much smaller than that of the other known elementary particles excluding massless particles.[1] The weak force has a very short range, the gravitational interaction is extremely weak, and neutrinos do not participate in the strong interaction.[4] Thus, neutrinos typically pass through normal matter unimpeded and undetected