The CLAS12 Low Threshold Cherenkov detector

Abstract The CLAS Cherenkov threshold gas detector was instrumental for electron identification in the Hall B 6 GeV era at Jefferson Lab. The detector’s scope has been modified for the new CLAS12 spectrometer to identify π + and π − for momenta greater than 3.5 GeV, thus becoming a Low Threshold Cherenkov Counter (LTCC). This was accomplished with a refurbishment of the gas container, its windows, mirrors, Winston light collecting cones, and photomultipliers. The design, construction, and performance of the refurbished LTCC are described. The lightweight mirrors and Winston cones have been re-surfaced with a highly reflective coating, the 5-in photomultiplier tube entrance windows have been treated with p-terphenyl to enhance the ultraviolet response, and the gas volume has been expanded to increase the thickness of the radiator gas and correspondingly the number of photoelectrons in the response signal. The LTCC response calibration has been performed on the single photoelectron signals, and the system efficiencies and response functions have been measured.