Silicon Photo-Multipliers (SiPMs) have been receiving a growing attention in the last years as they are considered an extremely promising replacement for traditional photomultiplier tubes (PMTs) for the detection of low-intensity light levels in many fields of application. The device is based on a matrix of small, passive-quenched silicon avalanche photodiodes operated in limited Geiger-mode (GM-APDs) and read-out in parallel from a common output node. Each element (referred to as either "microcell", "µcell" or "pixel") gives the same current response when hit by a photon, hence the total output signal is proportional (for moderate fluxes) to the number of hit µcells. The advantages of SiPMs over conventional PMTs are numerous: insensitivity to magnetic fields, low voltage operation, low power consumption, comptactness and low cost.
FACTOR (Fiber Apparatus for Calorimetry and Tracking with Optoelectronic Read-out) is a 3-year R&D project started at the beginning of 2007. The birth of this project was motivated by a strong interest for both the development of the device itself and for its future applications, especially to the read-out of fibre calorimeters in High Energy Physics (HEP) and scintillator read-out for Time of Flight (TOF) systems in space experiments. FACTOR's experimental program foresees an active collaboration with FBK-irst (Trento, Italy) that has recently fabricated SiPMs with different size and layout, featuring excellent overall performance. The first year of the project (2007) was mainly dedicated to device characterization and analysis. In particular, the first objective of FACTOR was the achievement of a thorough understanding of both capabilities and limits of SiPMs by studying, measuring and comparing, in different environmental conditions, the most critical device parameters for SiPMs fabricated by different producers.
In the next two years (2008 and 2009) our experimental program foresees to:
- Study the radiation effects (both surface and bulk damage) on SiPMs from different producers.
- Perform Photo Detection Efficiency (PDE) and time resolution measurements on the SiPMs.
- Construct and test on a particle beam a full plane of extruded plastic scintillators read-out via wls fibers coupled to circular SiPMs by FBK-irst.
- Construct and test a small-size prototype lead-fiber calorimeter read-out with FBK-irst circular SiPMs.
- Investigate the possibility to design a SiPM structure with backplane readout, in order to improve since the geometrical efficiency of the device and simplify the connection with the front-end electronics.