Auto-triggerable HPD sensors fully readout on ethernet: Applications for high-energy physics and medical imaging

The OPERA project is dedicated to neutrino oscillation search in the CNGS neutrino beam from CERN to Gran Sasso (Experimental Proposal, CERN/SPSC 2000-028, SPSC/P318, LNGS P25/2000, July 10, 2000). The experiment is designed to characterize the interactions of nu//tau resulting of the nu//mu yields nu//tau oscillation. The main element of the detector is a brick 10.2 cm multiplied by 12.8 cm cross- section consisting of 56 emulsion sheets 100 mum wide, interleaved with 1 mm lead plates. These bricks are assembled in walls of similar to 7 m side. A total of 72 walls is foreseen for the OPERA experiment with a total fiducial mass of 2 ktons. When a neutrino interaction occurs, the tracks of the charged particles are recorded in the emulsions with a high accuracy and the topology of the event is fully reconstructed with an automatic scanning of the emulsions. The role of the target tracker in OPERA is to locate the brick where the primary neutrino interaction occurs, to provide triggers and to make a coarser reconstruction of the events. It consists of two planes of scintillator strips located after a brick wall. The scintillation photons are collected by WLS fibers and read by a multi-pixels photodetector. We present results obtained with 61 pixels HPD's readout by auto-triggerable front-end electronics of the VA-TA series. We have also developed a new kind of acquisition system based on Ethernet, able to read the front-end electronics and deliver the data directly to the Ethernet network. The full readout chain from the scintillator to the DAQ has been tested with cosmics and with beams from the CERN PS. The acquisition scheme is being proposed for the OPERA DAQ system and can be implemented for medical applications with various photodetectors. A prototype of micro-Positron Emission Tomograph (microPET) is being build on this scheme in collaboration with other Rhone-Alpes Institutes.