Study of 144-ch Hybrid Avalanche Photo-Detector with high density electronics system for Belle-II RICH counter

For the Belle-II detector, we are conducting R&D on proximity focusing ring imaging Cherenkov (RICH) detector using a silica aerogel as a radiator. A 144-channel HAPD (Hybrid Avalanche Photo Detector) is adopted as a photo-detector for the Aerogel-RICH. Because the typical gain of HAPDs is lower than conventional photomultipliers, we need high-gain and low-noise electronics for readout of the HAPD. In addition, the electronics system should be sufficiently compact. For these reasons, we have designed and fabricated readout chips for the HAPD signal processing, based on ASIC (Application Specific Integrated Circuit) technique. We performed a test beam experiment of a prototype Aerogel RICH counter. In this test, it is found that Cherenkov rings are well reconstructed with the developed electronics system, and the ASIC shows excellent performance to be used for the aerogel RICH system. A present concern is a neutron tolerance of HAPDs. We have been studying how much possible radiation damage caused by neutrons can be reduced by optimizing the ASIC parameters without decreasing sensitivity for Cherenkov photons. It has been found that the radiation damage by neutrons considered in the Belle-II can be cured by shortening the shaping time of the amplifier in the ASIC. In this paper, we will report the performance of the ASIC chips that were used in the beam test and new version that is under development will be also explained.