An electron trigger based on transition radiation detectors

We present the Transition Radiation Detectors (TRD), coupled with the electron trigger, which were designed and built for selecting rare decays of neutral kaons in the KTeV experiment at Fermilab. The TRD is a powerful detector for identification of electrons in off-line analysis. A pion-electron rejection factor of 300:1 can be achieved with the KTeV TRD system. The electron trigger also uses signals from the TRD to discriminate electrons on-line. A system of programmable LeCroy 2366 modules runs a pattern recognition algorithm on TRD output with applied pulse height thresholds. A decision on the number of electrons which passed through TRDs is made in less than 500 nanoseconds. A desirable trigger rate suppression or signal efficiency can be achieved by choosing initialization constants for particular experimental conditions. During the experimental run the TRD trigger provided a required trigger rate suppression factor of 1.7-6 with signal efficiency of 97%-85%. In this summary paper we describe briefly the TRD, the main trigger components, and ifs functions. The performance of the TRD and the electron trigger in the KTeV experiment is also summarized.