Particle Detectors

The ultimate in particle detectors are probably those being used and constructed at large national and international laboratories such as Fermilab in Illinois and CERN in Geneva, Switzerland. At these locations colliding beam accelerators have been built which produce collisions of fundamental particles, such as electrons and positrons at CERN, and protons and anti-protons at Fermilab. At various points around these large circular accelerators the counter rotating beams cross, and head-on collisions can take place making large amounts of energy available for the production of other particles. Huge detectors costing millions of dollars and requiring hundreds of physicists to run them, are constructed surrounding these collision points. At Fermilab, two of these large devices, one called CDF and the other DZero, have recently reconstructed events, produced in these collisions, which provide strong evidence for the existence of the long sought top quark. To do this the detectors are designed to detect as many of the millions of particles produced in these collisions as possible. At DZero about 400,000 proton-anti-proton collisions occur per second. The detectors, weighing thousands of tons, are constructed in layers and almost completely surround the collision points. They utilize most of the detection techniques discussed above including scintillators, solid state detectors and devices similar to wire chambers which provide much improved performance. These are called silicon microstrip detectors. They are made up of closely spaced strips of silicon detectors which give very fast position measurements of particles accurate to about 0.01 mm. The thousands of individual detectors and detector systems are connected to computers which help select the very special events that might involve the top quark from the millions that do not.