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Introduction to the DELPHI experiment

The LEP Accelerator
Modern science of particle physics is heavily based on high energy accelerators, which produce wide range of elementary particles for consecutive studies. For precision analysis, electron-positron colliders are factories which provide scientists with sufficient statistical material of high purity. The biggest contemporary accelerator of this kind has been built in the European Particle Physics Laboratory, CERN. The CERN Large Electron Positron (LEP) collider is a 26.67 km circumference electron-positron storage ring, which is designed to operate in an energy range of 20 GeV to 50 GeV per beam at the first stage (LEP1) and up to 90 GeV at the second stage (LEP2). The basic feature of the LEP design is a large accelerating ring circumference in which the machine is installed in stages corresponding to the new physics events that are predicted by the unified theory of weak and electromagnetic interactions. The first such event is the Z⁰ boson at an energy of about 90 GeV. Since these bosons can be produced singly, the LEP1 machine energy was about 45.6 GeV per beam, giving 91.2 GeV in the centre of mass. The next important event is the production of pairs of the charged intermediate bosons (W⁺W^-) at an energy of about 180 GeV, which requires LEP2 energies of about 90 GeV per beam.