Novel photon detectors for focusing DIRC prototype

For present BaBar DIRC, the Cherenkov angular resolution is dominated by three contributions—the chromatic error, bar thickness and pixel size. We have designed the Focusing DIRC prototype, which potentially can reduce the chromatic error by a precise timing in the range of 50–100 ps per photon, and the bar thickness by a focusing mirror. This paper describes two novel photon detectors, which are candidates for this type of concept: Hamamatsu 64-channel multi-anode Flat Panel H-8500 PMTs and Burle 64-channel micro-channel plate MCP-PMTs. The detectors were tested with a PiLas laser diode light pulse providing 35 ps FWHM timing resolution. A single-photon timing resolution of (1) σ∼120–140 ps was achieved with the Hamamatsu PMTs, and (2) σ∼55 ps with the Burle MCP-PMTs. To achieve the good timing resolution results, we have developed a new fast amplifier and a constant-fraction discriminator. We have also developed a computer-controlled scanning setup, which allows a detailed study of the relative efficiency response to single photons.