# 1.2: A Timeline of Particle Physics


Year Experiment Theory
1927 $$\beta$$ decay discovered
1928 Paul Dirac: Wave equation for electron
1930 Wolfgang Pauli suggests existence of neutrino
1931 Positron discovered
1931 Paul Dirac realises that positrons are part of his equation
1933/4 Fermi introduces theory for $$\beta$$ decay
1933/4 Hideki Yukawa discusses nuclear binding in terms of pions
1937 $$\mu$$ discovered in cosmic rays
1938 Baryon number conservation
1946 $$\mu$$ is not Yukawa’s particle
1947 $$\pi^{+}$$ discovered in cosmic rays
1946-50 Tomonaga, Schwinger and Feynman develop QED
1948 First artificial $$\pi$$’s
1949 $$K^{+}$$ discovered
1950 $$\pi^{0}\rightarrow \gamma\gamma$$
1951 ”V-particles” $$\Lambda^{0}$$ and $$K^{0}$$
1952 $$\Delta$$: excited state of nucleon
1954 Yang and Mills: Gauge theories
1956 Lee and Yang: Weak force might break parity!
1956 CS Wu and Ambler: Yes it does.
1961 Eightfold way as organising principle
1962 $$\nu_{\mu}$$ and $$\nu_{e}$$
1964 Quarks (Gell-man and Zweig) $$u,d,s$$
1964 Fourth quark suggested ($$c$$)
1965 Colour charge all particles are colour neutral!
1967 Glashow-Salam-Weinberg unification of electromagnetic and weak interactions. Predict Higgs boson.
1968-69 DIS at SLAC constituents of proton seen!
1973 QCD as the theory of coloured interactions. Gluons.
1973 Asymptotic freedom
1974 $$J/\psi$$ ($$c\bar c$$) meson
1976 $$D0$$ meson ($$\bar u c$$) confirms theory.
1976 $$\tau$$ lepton!
1977 b (bottom quark). Where is top?
1978 Parity violating neutral weak interaction seen
1979 Gluon signature at PETRA
1983 $$W^{\pm}$$ and $$Z^{0}$$ seen at CERN
1989 SLAC suggests only three generations of (light!) neutrinos
1995 t (top) at 175 GeV mass
1997 New physics at HERA (200 GeV)

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