Performance of large area proximity focused hybrid photo-diodes

We are considering the possibility of using large area proximity focused HPDs to read out the Cherenkov light from aerogel blocks in B-factory experiments. This requires a photon detector with high immunity to magnetic field, large geometrical acceptance and high sensitivity to the single photoelectron. sponse of several large area proximity focused HPDs in high magnetic field has been studied. Results showing their substantial immunity to the magnetic field over a wide angular range are discussed. Large area HPDs imply large detector capacitance and reverse current, which are important parameters limiting the signal to noise ratio. In spite of this, excellent single pe sensitivities have been obtained with a commercial charge preamplifier readout.