What holds the proton together?— science newsSeptember 16, 1972
An experiment… at the CERN Laboratory in Geneva… gives an important clue about the structural arrangements deep within the proton… The result suggests the existence of a new and very strong fundamental interaction: the process that sustains [quarks] together inside protons… Various theorists have speculated on its nature and have even proposed an intermediate particle for it called a gluon.
Physicists finally found evidence of gluons in 1979, in the aftermath of electron-positron collisions in a German particle accelerator (SN: 4/21/79, p. 262). Gluons bind quarks into protons through the strong force, the most powerful force in nature. Recent research on the role of gluons within the proton suggests that the energy of the particles makes up about 36 percent of the mass of the proton (SN: 12/22/18 and 1/5/19, pg. 8). Future particle accelerators could measure the contribution of gluons to the proton internal pressurewhich averages a million trillion trillion times the strength of Earth’s atmospheric pressure (SN: 6/9/18, pg. 10).