The Particle Zoo
Discovered in cosmic rays:
- Positron, 1932, M = 0.511 MeV, anti-electron predicted by Dirac Eqn.
- Muon, 1938, M = 106 MeV
- Pion, 1947, M = 135 MeV, predicted by Yukawa to carry strong force
1 MeV = energy electron gains when accelerated across 1 million volts.
Discovered in particle accelerators by 1960:
- Kaon, rho, omega, … (Mesons, like pion)
- Lambda, Sigma, Xi, … (Baryons, like proton)
Mesons and Baryons feel the strong nuclear force
Leptons (electron, muon) do not