Abstract
Quantum chromodynamics should need little introduction, since it already permeates almost all descriptions of strong interaction phenomena nowadays. We recount here very briefly the basic motivation, beginning with some factual evidence:
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1.
Quarks of fractional charge and three colors seem to be required as constituents of hadrons in order to understand the spectrum of hadrons and their resonances.
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2.
The ratio of electron-quark to neutrino-quark deep inelastic scattering argues strongly for fractional charge of the quarks.
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3.
In addition to the spectroscopic evidence, the observed width of the decay πo → 2γ and the large cross section for e+e− → hadrons is successfully understood provided there are 3 colors of quarks.
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4.
The color-symmetry should be exact (or very nearly so); otherwise we would expect additional low-lying color non-singlet hadron states, states for which there is no empirical evidence.
Work supported by the Department of Energy under contract number DE-AC03-76SF00515.
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References
If you don’t know, you are invited to consult someone else’s lectures.
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Bjorken, J.D. (1982). Elements of Quantum Chromodynamics. In: Lectures on Lepton Nucleon Scattering and Quantum Chromodynamics. Progress in Physics, vol 4. Birkhäuser, Boston, MA. https://doi.org/10.1007/978-1-4899-6691-9_5
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