The barrel DIRC detector for the P¯ANDA experiment at FAIR

The P ¯ ANDA experiment at FAIR will perform high precision experiments in the charmed quark sector using cooled antiproton beams of unprecedented intensities of L=2×1032 cm−2 s−1 in the momentum range of 1–15 GeV/c. The charged particle identification in the barrel region needs a thin detector operating in a strong magnetic field. A ring imaging Cherenkov detector using the DIRC principle is an excellent match to those requirements. This article describes aspects of the design and R&D for the P ¯ ANDA barrel DIRC detector. The availability of highly pixelated fast photon detectors allows several key improvements compared to the successful BaBar-DIRC detector, some of which were tested in a proton beam at GSI. The optical properties of the radiator bars, made from synthetic fused silica, are critical to the success of the DIRC. Measurements of the attenuation length and reflection coefficient allow the determination of the surface roughness of prototype radiator bars.