Golden Jubilee Photos. Challenging Theory

Theory might provide the scaffolding of physics, but it takes experiments to put up the brickwork. The Large Electron-Positron Collider project (LEP), which included four experiments (ALEPH, DELPHI, L3 and OPAL), was designed to test the Standard Model of particle physics.


This is the muon spectrometer in the L3 detector with the magnet doors opened, 1993. L3's magnet will be a component in the ALICE experiment working with the LHC.

With more than 17 million Z boson decays observed in the first five years, and 40 thousand W boson pairs collected later, LEP allowed physicists to test the Standard Model to an unprecedented level of precision. LEP also measured the number of families of matter particles (three), and predicted the mass of the Top quark, which was later discovered in the US.
Occasionally, the LEP data showed small anomalies, but most of them disappeared after closer scrutiny: mainly, it revealed the coherent pattern of particle physics that the Standard Model had predicted.
Perhaps the most tantalising result came at the end of LEP's 11-year career when it saw signs of what might have been a Higgs boson, the particle thought to be responsible for the existence of mass. However, the data at hand did not allow the observation to be confirmed, so the result was only "perhaps".
LEP closed in 2000 to make way for the LHC, which will continue to challenge the Standard Model. However, LEP generated a body of work that will be useful for years to come, even after the Standard Model is superseded.


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