The Discovery of the Gluon

Soon after the postulation of quarks, it was suggested that they interact via gluons, but direct experimental evidence was lacking for over a decade. In 1976, Mary Gaillard, Graham Ross and the author suggested searching for the gluon via 3-jet events due to gluon bremsstrahlung in e+e − collisions. Following our suggestion, the gluon was discovered at DESY in 1979 by TASSO and the other experiments at the PETRA collider. Contribution to the book ‘50 Years of Quarks ’ to be published by World Scientific KCL-PH-TH/2014-36, LCTS/2014-35, CERN-PH-TH/2014-178 1. Quarks are Not Enough When Murray Gell-Mann postulated quarks [1] and George Zweig postu-lated aces [2] in 1964 as the fundamental constituents of strongly-interacting particles, several questions immediately came to mind. What are the super-strong forces that bind them inside baryons and mesons? Are these forces carried by other particles, perhaps analogous the photons that bind electrons to nuclei inside atoms? But if so, why do we not see individual quarks? What is the important intrinsic difference between the underlying theory of the strong interactions and quantum electrodynamics (QED), the unified quantum theory of electricity and magnetism? It was natural to suppose that the forces between quarks were mediated by photon-like bosons, which came to be known as gluons. If so, did they 1 a