Toward minimum ionizing particle detection using scintillating fibers and avalanche photodiodes

Scintillating fibers are potentially competitive with silicon microstrip detectors for moderately high resolution (~100 μm) particle tracking in high-energy physics experiments. Realizing this potential requires the development of a compact, efficient, and high-speed readout. The feasibility of using avalanche photodiodes (APD) for the detection of minimum-ionizing particles in submillimeter scintillating fibers is assessed. In tests to date, the expected small signal has been overwhelmed by amplifier noise. The fact that APD noise was a negligible contribution, even at an APD gain of 300, was verified by observing that the pulse-height spectrum with and without APD bias voltage showed no difference, and the RMS width of the distribution was consistent with the amplifier noise. Contemplated improvements to the apparatus include using veto counters to restrict the qVt triggers to β rays definitely passing through the fiber (which should improve the signal-to-noise by a factor not more than ≈(6 mm/1 mm)=6), and constructing an adjustable mount to allow optimal centering of the fiber relative to the APD´s sensitive area