Operation and performance of the Cosmic Ray Tracking (CRT) detector system

Abstract

The cosmic ray tracking (CRT) detectors consist of two drift chambers of the TPC type and an iron plate as a muon filter between the two chambers. CRT detectors are designed to detect and identify secondary cosmic ray particles in extensive air showers. Each detector has a local electronics box with a readout, trigger, and monitoring system. The local computers at the detector stations are used for hit and track finding in parallel to the detector readout. Detector stations are permanently calibrated online, using the cosmic ray data. The online software, including data processing and calibration procedures, are presented in this paper. Ten detectors are in operation at the site of the HEGRA air shower array. The detector performance has been evaluated using data from these detectors and the HEGRA array as well as by Monte Carlo simulations. The spatial resolution has been found to be about 1 mm both in drift and in wire direction. The corresponding angular resolution is about 0.4° in each projection for a single track. Muons are usually identified if scattered by less than 2.5° in the iron plate, corresponding to energies above about 1 GeV. In HEGRA-triggered showers an overall muon identification efficiency of 87% is achieved, with a fraction of only 0.07% of the electrons being misidentified as muons.