# 7th International Workshop on Ring Imaging Cherenkov detectors (RICH 2010)

2-7 May 2010
Oustau Calendal Conference Center
Europe/Paris timezone
If you participated in the conference, please consider sending photos and poster contributions, unless done so already!

## Study of 144 Channel Multi-Anode Hybrid Avalanche Photo-Detector For the Belle-II RICH Counter

4 May 2010, 14:30
25m
Oustau Calendal Conference Center

#### Oustau Calendal Conference Center

Cassis, France
Oral presentation Photon detection for Cherenkov counters

### Speaker

For the Belle-II experiment, we have been developing a proximity focusing RICH counter with silica aerogel radiator as a new particle identifier in the forward endcap to extend the $¥pi/K$ separation capability up to 4 $¥sigma$ at 4 GeV/c. Our requirements on a RICH photon detector are the following: (1) sensitivity to single photons, (2) immunity to magnetic field, (3) granularity of $¥sim5$$¥times5$ mm$^2$, (4) large effective area, (5) compact size due to the limited available space. To fulfill these conditions, R¥&D on a new hybrid avalanche photo-detector (HAPD) has been conducted with HPK for several years. In this device, vacuum tube with a bi-alkali photocathode is coupled to an avalanche photo-diode (APD), which is pixelated into $6¥times6$ pads, each of which is $5¥times5$ mm$^2$; 1 HAPD accommodates 4 APD chips, amounting to 144 pads total. More than 10 HAPDs have been newly produced since 2008. Fundamental features of HAPD samples were examined using a light source at the lab. Total gain was obtained to be about $5¥times10^4$ and a clear single photon signal was detected. Basic operations of HAPD under an axial magnetic field of 1.5 Tesla was also studied and the cross-talk due to electron back-scattering was very much suppressed and single photon sensitivity was improved. Recently, a new HAPD with high QE was successfully fabricated, and a QE exceeding 30 ¥% could be confirmed. With these HAPD samples, a RICH prototype counter was built. In this set-up, a $2¥times3$ HAPDs were arranged with a custom-made ASIC readout system, by which signals were amplified and digitized. A test beam experiment was including the latest beam testcarried out in November 2009 at KEK. We obtained 2.5 times larger photoelectron yield with 40 mm-thick aerogel radiator compared to the previous beam test, and from these results the $¥pi/K$ separation capability exceeding 5$¥sigma$ at 4 GeV/c was demonstrated. In this report detail results of HAPD studies will be presented.