Evidence for Quarks Theoretical Reasoning Experimental Principles Experimental Evidence Discovery of Each Quark Type: Up/Down Charmed/Strange Top/Bottom

Theoretical Reasoning Murray Gell-Mann and George Zweig (1964) Prediction of the Ω- and mass, precisely, based on the known existence and mass of the Ξ particle. Natural assumption made-these, and many other, particles are bound states of more fundamental particles-quarks.

Experimental Principles The inelastic scattering of waves when collided with nucleons demonstrated point-like inner particles. (Feynman’s partons) Needed very high momentum particles to “probe” the “insides” of the nucleons. (Remember: λ=h/p)

Experimental Evidence Shown in experiments as early as 1956 at SLAC and MIT. Led to the quark-parton model Same principle as used in Rutherford’s experiment that proved existence of nucleons.

Discovery of Quark Types Experiments mentioned previously, taken as proof of the Up, Down and Strange quarks. These three quarks alone explained the majority of hadrons observed, though more later were needed theoretically and found experimentally. Charmed quark discovered in 1974 at BNL and SLAC. Bottom quark discovered in 1977 at Fermilab. Top quark discovered in 1995, also at Fermilab.