How a walk through CERN's corridors helped lead to the discovery of the gluon 40 years ago

How a walk through CERN’s corridors helped lead to the discovery of the gluon 40 years ago
A three-jet event detected by the TASSO detector at DESY. Credit: Oxford PPU

Forty years ago, in 1979, experiments at the DESY laboratory in Germany provided the first direct proof of the existence of gluons—the carriers of the strong force that "glue" quarks into protons, neutrons and other particles known collectively as hadrons. This discovery was a milestone in the history of particle physics, as it helped establish the theory of the strong force, known as quantum chromodynamics.

The results followed from an idea that struck theorist John Ellis while walking in CERN's corridors in 1976. As Ellis recounts, he was walking over the bridge from the CERN cafeteria back to his office, turning the corner by the library, when it occurred to him that "the simplest experimental situation to search directly for the gluon would be through production via bremsstrahlung in electron–positron annihilation." In this process, an electron and a positron (the electron's antiparticle) would annihilate and would occasionally produce three "jets" of particles, one of which being generated by a gluon radiated by a quark–antiquark pair.

Ellis and theorists Mary Gaillard and Graham Ross then went on to write a paper titled "Search for Gluons in e+-e– Annihilation" in which they described a calculation of the process and showed how the PETRA collider at DESY and the PEP collider at SLAC would be able to observe it. Ellis then visited DESY, gave a seminar about the idea and talked to experimentalists preparing to work at PETRA.

A couple of years later, and following more papers by Ellis, Gaillard and other theorists, PETRA was being commissioned and getting into the energy range required to test this theory. Soon after, at the International Neutrino Conference in Bergen, Norway, on 18 June 1979, researchers presented a three-jet collision event that had just been detected by the TASSO experiment at PETRA.

At the European Physical Society conference at CERN a couple of weeks later, the TASSO collaboration presented several three-jet events and results of analyses that showed that the gluon had been discovered. One month later, in August 1979, three other experiments at PETRA showed similar events that lent support to TASSO's findings.

Find out more about the discovery in DESY's coverage of the 40-year anniversary, in Ellis' account, and in this 2004 CERN Courier article.

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Jun 18, 2019
Why does our world have a particular non-zero baryonic number? The term "asymmetry of baryogenesis" does not explain anything; this is simply a statement of fact. The availability of the energy is a necessary but not sufficient condition. The method of creation of the matter, our universe consists of, was different than that in accelerators. The space and its evolution are the primary sources of phenomena in Mega- and micro-worlds. Thus cosmology and particle physics have the same active agent - physical space.

Jun 18, 2019
the "reason" this Universe works?
because it is imperfectly formulated out of chaos.

a "perfect universe with all hydrogen elementary particles, evenly distributed throughout Space? would be timeless, formless, no energy but the slow, slpw drag of gravity.

& by the way, totally lifeless.

wgat we have is a universe of random actions. phenomena constantly interfering with each other,

with my theory of stupid design?
i have fun blaming the cthonic incompetency of irresponsible drunken hooligan deities.

hey! if they insist on taking credit for the good things in life?
they damn well are going to have to take the blame for all the cosmic failures!

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