Pixel HPD

The pixel HPD is being developed in close collaboration with DEP [4]. It is based on standard image intensifier technology that strongly focuses photoelectrons onto a segmented silicon pixel array. The feasibility of this approach has already been demonstrated with the `IPSA-tube' [5]. Work is ongoing on a scale model prototype with an active photocathode diameter of 40 mm and an anode diameter of 11 mm. The anode is assembled with the LHC1 chip developed at CERN [6]. This chip contains a detector array of 2048 pixels, 50 x 500$\mu$m² in size and it has a lowest achievable comparator threshold of 4000e^- with a spread of 1000e^-. Unfortunately these detector properties are not compatible with the needs of LHC-B. In particular, the pixel dimension (50$\mu$m) is too small compared to the RICH granularity ( 500 x 500$\mu$m²). Nor are the the threshold properties of the LHC1 chip compatible with LHC-B requirements, though recent development in pixel electronics have achieved comparator thresholds down to 1400e^- with an RMS of 90e^-. The specific needs of LHC-B are being investigated.