Coincidence Resolving Time Improvement by Energy-Time Correlation

In particle-particle coincidence experiments with semiconductor detectors, the chief limitation on resolving time often lies in the time required for charge collection, particularly if the energy ratio of the two detected particles varies over a wide range. However, the penetration depth of the particles and hence their collection time is a function of their energy. By measuring the arrival time difference for the two "coincident" signals, one may compare the timing with the energy and select only those events whose timing is appropriate to their energy. The time measurement has been carried out by using fast circuits to provide time-overlap signals, digitized into a few channels by a stacked discriminator. This information, along with the digitized energy signals, was fed to an on-line SDS 910 computer, which selected events according to a previous time-energy calibration. This calibration method was strictly empirical: the time and energy were initially recorded for all time channels simultaneously. On the basis of this data different parts of the kinematic line were assigned with a light pen to appropriate time channels, overlapping where necessary. The initial application of this method to the reaction H1(d,2p)n where the particle energies varied over a 20 to 1 range resulted in a factor of 3 improvement in the original 75 ns resolving time, using only 4 time channels. Twelve additional time channels now available should result in a considerable further improvement.