The ALEPH Detector

This is a clickable map, to learn about the parts of the detector click on the part you are interested in. For a more accurate printable view of the detector pick the postscript file: detector.

ALEPH is a particle detector covering as much of the 4pi solid angle as possible. It is designed to measure the momenta of charged particles, to measure the energy deposited in calorimeters by charged and neutral particles, to identify the three lepton flavors, and to measure the distance of travel of short-lived particles such as the tau lepton and the b and c hadrons.
Particular emphasis has been given to
momentum resolution up to the highest energies (by means of a tracking system in a 1.5 T magnetic field),
electron identification (by means of a highly segmented, projective electromagnetic calorimeter as well as by ionization measurement in the tracking system),
muon identification (with sufficient absorber to eliminate the hadrons).
photon resolution (with the fine grain electromagnetic calorimeter).

The structure of the detector. It is like an onion with the light tracking components inside and the heavy calorimeters around. We can look at the detector starting from the centre, the interaction point. For this, look at the insert at the bottom left of the picture, this is a blow up of the central region.

The tracking involves three detectors:
a vertex detector, VDET, composed of two layers of double-sided silicon microstrips,
a drift chamber, ITC, with a 30 cm outer radius, and
a time projection chamber, TPC, with 180 cm outer radius.

Then the calorimetry proceeds in two stages: electromagnetic and hadronic.
The electromagnetic calorimeter, ECAL, is a 45 layer lead/proportional chamber sandwich,
the hadron calorimeter, HCAL, is a 23 layer iron/streamer tube sandwich with total thickness of 120 cm of iron (the magnet return yoke).
The whole is surrounded by an additional muon detection system, MUON, of two double layers of streamer tubes.
Finally, important for precise cross section measurement is the highly segmented luminosity calorimeter composed of twelve-layer tungsten/silicon sandwiches that surround the beam pipe at each end.