Seeing gluons at LEP
8 September 1999
The first views of gluons - the carriers of the strong force between quarks - came from the electron-positron collider PETRA, at the DESY laboratory in Hamburg, in 1979. Ten years later, the Large Electron Positron (LEP) collider started up at the European Laboratory for Particle Physics, CERN. With a total collision energy 30 times greater than PETRA's, LEP provided a clearer view still into the radiation of gluons by quarks and antiquarks produced when electrons and positrons (antielectrons) annihilate.
This "event" shows the collision of an electron with a positron at the centre of the ALEPH detector, which has created four ‘jets’ of particles. The electron and positron have annihilated to produce a quark and an antiquark, each of which created a jet of particles. One possibility for the other two jets is that they orginated from two gluons, radiated by the quark or antiquark. Other explanations are also possible, but they all involve the appearance of one or more gluons. By studying many examples like this, the physicists working on ALEPH and the other detectors at LEP have been able to build up a detailed picture of the underlying processes. You can see a similar event with three jets, and therefore a single gluon, here.
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