1933

Fermi develops his theory of weak interaction that includes the neutrino

Italian physicist Enrico Fermi introduced the name “neutrino” in 1932 at a conference in Paris. Meaning “little neutral one” in Italian, “neutrino” was adopted to differentiate Pauli’s hypothesized “neutron” particle from a massive nuclear particle discovered by James Chadwick in 1932, which was also called the neutron.

In 1933, Fermi developed his theory of beta decay that included the neutrino, which he assumed to be massless (or otherwise have a very small mass) and chargeless. Fermi’s theory was the precursor to the theory of the weak nuclear force—the third fundamental force of nature (after gravity and electromagnetism but before the strong nuclear force). The theory also showed that beta decay could run in reverse, which happens to be the underlying principle that allows IceCube to work.

A diagram of beta decay
Beta decay in an atomic nucleus (the accompanying antineutrino is omitted). The inset shows beta decay of a free neutron. In both processes, the intermediate emission of a virtual W− boson (which then decays to electron and antineutrino) is not shown.