**This page was archived on 1 December 2008
as the content is out of date**
The 27 kilometre circumference LEP machine at CERN (the European Laboratory
for particle physics) ran from 1986 until 2000, colliding electrons with their
antimatter partners, positrons.
When an electron and a positron collide, they disappear in a burst of energy
which, almost immediately, changes back into particles. LEP was designed so
that the collisions took place inside four detectors where the particles
produced could be studied in detail. The Science and Technology Facilities
Council was involved in funding the construction and operation of three of
these detectors: ALEPH (Apparatus for LEP Physics at CERN), OPAL (the
Omni-purpose Apparatus at LEP) and DELPHI (Detector with Lepton, Photon and
Hadronic Identification at LEP.
The nature of the particles generated in these collisions depends upon the
speed, or energy, of the colliding electrons and positrons. Between 1989 and
1995 their energy was tuned exactly to the value needed to create Z0
particles, the neutral carrier of the weak nuclear force. Between 1996 and
2000, the collision energy was increased to produce two heavier particles, the
W+ and W-, the charged carriers of the weak neutral force. The detection and
study of millions of these three particles has allowed LEP to make extremely
precise tests of the standard model of particles and their interactions.
Although the LEP project has now finished, with the collider being removed
to make way for the Large Hadron Collider which is to be built in the same
tunnel, the analysis of the enormous quantity of data generated by the LEP
experiments continues.
Page last updated: 01 December 2008
by Charlotte Jamieson
