Construction and Operation of a Large Ring-Imaging Cerenkov Detector

We have constructed a large-aperture ring-imaging Cerenkov counter, intended to identify high momentum hadrons in a high pt experiment at Fermilab (E605). To date we have performed a preliminary analysis on a small subset of our data, taken during the initial operation of our counter (April-June 1982). We have obtained ?/K separation with good efficiency from about 60 GeV/c to 120 GeV/c in momentum under high luminosity conditions (~5 × 109 protons/second on target). Approximately 84% of all single-track events having at least one detected photon have been unambiguously identified. Cerenkov photons were detected by a multi-step avalanche chamber via the photoionization of triethylamine (TEA) vapor, and a mean number of 2.8 photons per event was detected for the highest velocity particles. Improvements in photon reconstruction are expected, especially as we refine our tracking procedures.