OPAL

The Omni Purpose Apparatus for LEP Detector is designed to "provide precise measurements of charged particles and of electromagnetic energy over nearly the full solid angle" [1]. During LEP1 (1989-1995), OPAL collected millions of events to make precision measurements of the Z[2]. During LEP2 (1996-2000), the physics goal was to search for new physics through W⁺W^- pair production.

Detector Design

The detector provides acceptance for Z^{0</sub> decays over <math>4\pi</math> in solid angle. The main detector components are a system of central tracking chambers inside a solenoidal field of 0.435 T, a time-of-flight counter, a lead glass electromagnetic calorimeter with a presampler, a hadron calorimeter in the form of an instrumented magnet return yoke, and an outer muon chamber. A forward calorimeter serves as a luminosity moniter.}

Central Tracking Detector

The Central Tracking Detector is divided into a precision vertex chamber, a large jet chamber, and a z chamber.

The vertex detector is a cylindrical drift chamber that surrounds has a length of 1 m, an inner radius of 88 mm, and an outer radius of 235 mm. There are two layers of 36 cells each: an inner layer of axial wires and an outer layer of stereo cells. Both types of cells have radial wire planes consisting of 200 <math>\mu m</math> gold plated Cu-Be potential wires and 20 <math>\mu m</math> gold plated W-Rh andoe wires. In the axial cells, there are 12 anode wires with radial spacing of 5.3 mm. The stereo cells have 6 anode wires with a spacing of 5 mm with a stereo angle of 4<math>\textdegree</math>. The cathode planes use 125 <math>\mu m</math> Cu-Be wires with a 1 mm spacing in both cells. In the <math>r-\phi</math> plane, the vertex chamber provides a resolution of 55 <math>\mu m</math>.

References

1. The OPAL Collaboration. "The OPAL Detector at LEP." CERN-PPE/90-114. August 14, 1990. 2. http://opal.web.cern.ch/Opal/