detectorsALEPH

ALEPH, short for Apparatus for LEP Physics, was a general-purpose particle detector at CERN's LEP collider in Geneva. It operated from 1989 to 2000 and was one of the four large detectors built for LEP, alongside DELPHI, L3, and OPAL. The primary mission was to study electron-positron collisions at the Z boson resonance and later at higher energies during LEP II, enabling precision tests of the Standard Model and searches for new phenomena.

Design and subsystems: The detector was a large, cylindrically symmetric apparatus arranged around the interaction point and enclosed in a superconducting solenoid producing a magnetic field to bend charged particles. The tracking system combined a silicon vertex detector with a large time projection chamber as the main tracker, providing momentum and vertex information. The inner detectors were followed by a highly segmented electromagnetic calorimeter for electrons and photons and a hadronic calorimeter for jets and missing energy. Muon chambers embedded in the magnet yoke completed the outermost layer for muon identification. The system was designed to deliver good momentum resolution, energy measurement, and particle identification across a broad range of angles and energies.

Impact: ALEPH contributed to precision measurements of the Z boson properties, including widths, branching ratios, and couplings, and to W-boson physics and searches for new phenomena. It also provided data used to test quantum electrodynamics and the electroweak sector and to constrain beyond-Standard-Model scenarios. After LEP’s closure, the detector was dismantled.