7 - Track detectors

Summary

Some scientists find, or so it seems, that they get their best ideas when smoking; others by drinking coffee or whiskey. Thus there is no reason why I should not admit that some may get their ideas by observing or by repeating observations.

Karl R. Popper

The measurement of particle trajectories is a very important issue for any experiment in high energy physics. This provides information about the interaction point, the decay path of unstable particles, angular distributions and, when the particle travels in a magnetic field, its momentum. Track detectors, used intensively in particle physics up to the early seventies, have been described in Chap. 6.

A new epoch was opened by the invention of the multiwire proportional chamber [1, 2]. Now gaseous wire chambers and micropattern detectors almost play a dominant rôle in the class of track detectors.

The fast progress of semiconductor detectors has resulted in a growth of the number of high energy physics experiments using tracking systems based on semiconductor microstrip or pixel detectors, especially in areas where extremely high spatial accuracy is required.

Multiwire proportional chambers

A multiwire proportional chamber (MWPC) [1–4] is essentially a planar layer of proportional counters without separating walls (Fig. 7.1).