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Linné on line arrow Physics and the Cosmos arrow Physics and the Cosmos arrow Quarks and leptons arrow An example of physics at LEP

An example of physics at LEP

In the Large Electron-Positron collider, LEP, at CERN high energy electrons and positrons were collided. During the period 1990–1995 one studied the production and decay of Z bosons and performed several precision tests of the electroweak theory which have verified the theory to very high accuracy. From 1996 to 2000 one increased the energy and studied among other things pair production of W bosons. One also searched for the Higgs boson and was able to put a limit on its mass.

In one of the experiments, DELPHI, a group from Uppsala participated. Their main contribution was to design and build RICH-detectors (Ring Imaging CHerenkov). These are especially useful for the identification of particles, which has been exploited in the analysis made by the group. The analysis has been focused on measuring parameters in the standard model with a high accuracy based on asymmetries in the particle production, for which particle identification is essential.

In collisions between an electron and a positron at LEP these two particles can be annihilated and form an intermediary vector boson. This boson can either be a Z boson, which is the more common at LEP, or a photon. The Z boson is not stable and quickly decays. In the decay a particle anti-particle pair is formed. This pair can be a lepton anti-lepton pair (electron positron, muon anti-muon, tau anti-tau or neutrino anti-neutrino) or a quark anti-quark pair.

System with two colliding beam particles. System with the target at rest.
By clicking and dragging on the picture at the same time as you press down the Ctrl-button you can zoom in and out. You can also move the picture sideways by pressing the Shift-button as you click and drag.

Of course, the collisions are normally not this simple but more complex with a much larger number of particles being produced. The DELPHI experiment has an online system which illustrates actual collisions.