Piecing OPAL together

31 May 2000

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OPAL, one of the four large detectors at the Large Electron Positron Collider (LEP) at CERN, Geneva, fits together rather like an interlocking puzzle. Like the other detectors, it consists of different layers that have specific roles in detecting and identifying the sprays of new particles produced at LEP. In this image, where the detector is pulled apart, various components are more easy to see. To the left is the cylindrical 3.7-m diameter "jet chamber", the main device for recording the tracks of charged particles. Projecting from this, above the two people, is the central "vertex detector", which helps to pin-point the decays of short-lived particles. During operation these chambers fit within each other inside the "bobbin"-like structure. This contains the coil of the electromagnet that provides the magnetic field to bend the tracks of charged particles.Two huge curved structures fit around the "bobbin" - the end of one of these is clearly visible to the right. These contain the calorimeters that measure the energy of particles and also help in their identification.

Credit: CERN Photo