Lepton ChartWeak Interaction
All stable matter is made from particles in just the first generation (except perhaps for the other neutrinos). A generation is a set of one of each charge type of quark and lepton, grouped by mass. The first generation contains the up and down quarks, the electron and the electron neutrino.
Physicists had thought that they understood all matter until the muon (µ), the first particle of the second generation, was discovered in 1936. It is said that the physicist, I.I. Rabi, asked,
when he heard of the new particle. One of the big puzzles not explained by the Standard Model is why the muon and the tau exist in addition to the electron. Without understanding this, we cannot rule out the possibility that there are more quarks and leptons, with yet larger masses than those we can produce.
Lepton ChartWeak Interaction
