1967 Steven Weinberg and Abdus Salam separately propose a theory that unifies electromagnetic and weak interactions into the electroweak interaction. They also predict an additional massive boson called the Higgs Boson that has not yet been observed. At the Stanford Linear Accelerator, in an experiment in which electrons are scattered off protons, the electrons appear to be bouncing off small hard cores inside the proton. Sheldon Glashow, John Iliopoulos, and Luciano Maiani recognize the critical importance of a fourth type of quark in the context of the Standard Model. A quantum field theory of strong interaction is formulated.
Quarks are determined to be real particles, carrying a color charge.
Gluons are massless quanta of the strong-interaction field. This strong interaction theory was first suggested by Harald Fritzsch and Murray Gell-Mann . The property is necessary to describe the 1968-69 data on the substrate of the proton. In a summary talk for a conference, John Iliopoulos presents, for the first time in a single report, the view of physics now called the Standard Model. If you want to understand the various aspects of the Standard Model, please explore the Standard Model Path .