Application of avalanche photodiodes for scintillating fiber readout

We are investigating the application of avalanche photodiodes (APDs) for readout of the signals of a scintillating fiber tracker for the CDF experiment at Fermilab. The unit of the tracking device is a 3 HF fiber doublet which consists of layers of 0.5 mm diameter fibers stacked with stagger by half a fiber diameter. Each APD array has 16 pixels of 1 mm diameter arranged in line. We tested the performance of the APD array using a conventional charge amplifier and shaping amplifier. In order to optimize the S/N ratio, we measured the signal and the noise as a function of the temperature and of the bias voltage. In the temperature range from -55 to +20 C, the S/N ratio was measured to increase with lowering the temperature. At temperatures below -20 C, a S/N ratio of better than 10 is achievable for ∼50 photons expected from the 3HF fiber doublet. (orig.)