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The OPAL Experiment at LEP 1989-2000

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OPAL was one of the major particle physics experiments at CERN. OPAL studied particles and their interactions by collecting and analysing electron-positron collision events at LEP, the Large Electron-Positron collider. LEP was the largest particle accelerator in the world. There were three other experiments at LEP: ALEPH, DELPHI and L3. You can take an interactive tour of the particle adventure or you can be a particle detective identifying interesting particle physics interactions taken by OPAL.

See also our OPAL physics results for particle physicists

 

12 years of physics at OPAL

The OPAL experiment and the LEP collider started operation in August 1989. Data taking finally ended on November 2, 2000. (`` The first and the last OPAL event''). The scientific evaluation of the data will continue for many more years.
The two phases of LEP operation were:
  • LEP1 (1989-1995) where millions of Z events were accumulated for high precision measurements. In these events the electron and the positron produce a single Z boson .
  • LEP2 (1996-2000) where the collision energy was increased to make W+W- pairs, and to search for possible new particles or physical effects

The links above lead to descriptions of the physics objectives of OPAL, and to pictures of typical electron-positron collision events.

 
An OPAL event
This event shows the annihilation of an electron and a positron. In this interaction, a pair of heavy charged particles, W+ and W- bosons, is produced. Each of them decays into two quarks which are finally detected as particle jets (rotating view) .

 

OPAL detector
A cut-away view of the OPAL detector
(photos from the installation).
 

The OPAL detector

The OPAL detector was a big general-purpose particle physics detector. OPAL took its name from the detector description: an Omni-Purpose Apparatus at LEP . You can take a tour of the detector.

and the people working with it

The OPAL collaboration is a team of physicists and engineers who designed, built and ran the OPAL detector, and who analyse the data collected. Currently the collaboration consists of about 200 physicists from 34 institutes in Canada, Germany, Hungary, Italy, Israel, Japan, the United Kingdom and the United States.


The OPAL Webweavers8 September 2005