ALEPH was a particle detector on the Large Electron-Positron collider (LEP). It was designed to explore the physics predicted by the Standard Model and to search for physics beyond it.

ALEPH first measured events in LEP in July 1989. LEP operated at around 91 GeV – the predicted optimum energy for the formation of the Z particle. From 1995 the accelerator operated at energies up to 200 GeV, above the threshold for producing pairs of W particles. 

The ALEPH detector was built in cylindrical layers around a beam pipe made of beryllium, with the electron-positron collision point in the middle. Working outwards from the beam pipe, ALEPH held a vertex detector composed of two layers of double-sided silicon microstrips; an inner drift-chamber that provided 8 tracking coordinates and a trigger signal for charged particles from the interaction point; a time projection chamber – 4.4 metres long and 3.6 metres in diameter – to detect charged particles; an electromagnetic calorimeter to identify electrons and photons; a hadron calorimeter to detect hadrons; and a superconducting coil, 6.3 metres long and 5.3 metres in diameter, to provide the 1.5 tesla magnetic field necessary to work out a particle's charge and allow measurements of momentum. The whole system was housed inside a 12-sided cylinder and surrounded by a muon-detection system.

The ATLAS and CMS detectors which appeared later on the Large Hadron Collider follow a similar "onion-layer" configuration to ALEPH.

Find out more on the archived ALEPH public pages