It was a circular collider with a circumference of 27 kilometres built in a tunnel roughly 100 m (300 ft) underground and passing through Switzerland and France.

Hadrons are composite particles (composed of quarks) and are relatively heavy; protons, for example, have a mass 2000 times greater than electrons.

This enables a high rate of collisions and facilitates collection of a large amount of data, which is important for precision measurements or for observing very rare decays.

In linear colliders, particles move in a straight line and therefore do not suffer from synchrotron radiation, but bunches cannot be re-used and it is therefore more challenging to collect large amounts of data.

As a circular lepton collider, LEP was well suited for precision measurements of the electroweak interaction at energies that were not previously achievable.

At the end of 2000, LEP was shut down and then dismantled in order to make room in the tunnel for the construction of the Large Hadron Collider (LHC).

The name of the experiment was a play on words, as some of the founding members of the scientific collaboration which first proposed the design had previously worked on the JADE detector at DESY in Hamburg.

Its data were used to make high precision measurements of the Z boson lineshape, perform detailed tests of the Standard Model, and place limits on new physics.

The lead glass blocks from the OPAL barrel electromagnetic calorimeter are currently being re-used in the large-angle photon veto detectors at the NA62 experiment at CERN.

[5] Its enormous octagonal magnet return yoke remained in place in the cavern and became part of the ALICE detector for the LHC.

Near the end of the scheduled run time, data suggested tantalizing but inconclusive hints that the Higgs particle of a mass around 115 GeV might have been observed, a sort of Holy Grail of current high-energy physics.

There was a proposal to extend the LEP operation by another year in order to seek confirmation, which would have delayed the start of the LHC.