Timing and detection efficiency properties of multi-anode PMTs for a Focusing DIRC

For the present BABAR-DIRC, the Cherenkov angular resolution is dominated by three contributions - the chromatic error, bar thickness and pixel size. This paper discusses a prototype for a Focusing DIRC, which uses a smaller pixel size, a focusing mirror to reduce the effect of the bar thickness and precise timing in the range of 50-100 ps per photon to reduce the size of the chromatic error. 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 85011-501 MCP-PMTs. The detectors were tested with a PiLas laser diode providing light pulses with 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 two-dimensional scanning setup, which allows a detailed study of the uniformity of the PMT and of the efficiency response to single photons relative to a reference PMT.