Wolfgang Pauli predicted the existence of a neutral particle in beta decay in 1930 as a way to resolve the problme of the continuous spectrum of beta particle energies.
The electron should just take away the energy released by the decay and have one kinetic energy. Instead, its energy varies from the theoretical value down to zero.
The neutrino proposed by Pauli splits the energy available with the electron randomly producing the energy spectrum or distribution observed.
It took until 1956 for the neutrino to be observed. Cowan and Reines Neutrino Experiment was carried out using a nuclear reactor to provide a high denisty of neutrinos.
Weak interaction meant that the chances of an event were rare.
The event observed was reverse beta decay.
$$ p + \bar{\nu}_e \rightarrow e^+ + n $$
The muon was discovered in 1936 from the study of high energy cosmic rays entering the upper atmosphere.
The particle was described as
that there exist particles of unit charge, but with a mass (which may not have a unique value) larger than that of a normal free electron7 and much smaller than that of a proton
Discovered by Anderson and Neddermeyer the particle was said to be a heavier state of the electron.
Muon mass is about 200 times that of the electron.
The tau was discovered in experiments conducted from 1974 to 1977 from the collision of electrons and positrons.
The production occurred during the production of other heavier leptons during electron positron annihilation at very high energies.
$$ e^+ + e^- \rightarrow e^\pm + \mu^\pm + \tau^\pm $$
Discovered by Perl and Reines at SLAC and Berkley. Both won the Nobel Prize for Physics in 1995 for their discovery.
Tau mass is about 3500 times that of the electron.
The muon neutrino was discovered in 1962 at Brookhaven using a beam of accelerated protons.
The protons produced a shower of \( \pi \) mesons. These travelled 70 feet to massive steel plates from old battleships. On their way the pions decaued into muons and neutrinos.
Only the neutrinos cold pass through the steel plates. They were detected by spark detectors which could trace the muons produced and prove the existence of the muon neutrinos.
Lederman, Schwartz and Steinberger were awarded the Nobel Prize for their discovery in 1988.
Although it was obvious the tau neutrino should exist after the tau was discovered in the 1970s, the tau neutrino was not discovered until 2000.
It was discovered at Fermilab a decade after the experiment was started.