Two charged pi mesons , with positive and negative charge, are discovered. The neutral pi meson is discovered. The lambda baryon and K meson are discovered. The electron neutrino , predicted by theory in 1930, is confirmed to exist. Lots of baryons and mesons being discovered, and their properties occur in regular patterns that look as if baryons and mesons are made of smaller building blocks.
Physicists exhibit a tendency to name new particles after letters in the Greek alphabet.
1963 Quark theory postulates that protons are made of smaller particles that carry charges that come in thirds of the electron charge. Deep inelastic scattering and other experiments reveal more of the quark structure inside protons and other hadrons. The tau lepton is discovered, making a triplet of charged leptons with the electron and muon, leading to predictions of a tau neutrino to accompany the electron neutrino and the muon neutrino. A fifth flavor of quark, named bottom , is detected in the newly discovered Upsilon meson. This pattern leads particle physicists to believe they will find a sixth and final flavor of quark some day.