50 years ago, physicists got a whiff of what glues together protons
In 1972, particle smashups hinted at the gluon, which we now know not only holds together the innards of the proton, but also makes up more than a third of its mass.
What holds the proton together— Science News, September 16, 1972
An experiment … at the CERN Laboratory in Geneva … gives an important clue to structural arrangements deep within the proton…. The result hints at the existence of a new and very strong fundamental interaction — the process that holds [quarks] together inside the protons.… A number of theorists have speculated about its nature and have even proposed an intermediate particle for it called a gluon.
Update
Physicists finally found evidence for gluons in 1979, in the aftermath of electron-positron collisions at a German particle accelerator (SN: 4/21/79, p. 262). Gluons bind quarks inside protons via the strong force — the most powerful force in nature. Recent investigations of gluons’ role inside the proton suggest the particles’ energy makes up about 36 percent of the proton’s mass (SN: 12/22/18 & 1/5/19, p. 8). Future particle accelerators could gauge gluons’ contribution to the proton’s internal pressure, which averages a million trillion trillion times the strength of Earth’s atmospheric pressure (SN: 6/9/18, p. 10).
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