Scintillating fibers coupled to photosensors provide flexible, fast and high granularity detectors which are able to work in a high rate environment. We will report about the performances obtained with several detector prototypes (single and multi-layers) based on 250 $\mu$m multi clad square scintillating fibers coupled to Hamamatsu silicon photomultiplier (SiPMs). Current measurements show results never reached up to now: very high detection efficiency for minimum ionizing particles (m.i.p.) already for a single layer (95%, mean collected light/fiber 8 phe), and full efficiency for multilayer configurations. Spatial resolutions $< 100 \mu$m are foreseen for single layer and much less for multilayer devices. Such spatial resolutions can be achieved by keeping the optical cross-talk between fibers at a negligible level ($<$ 1%), a level which we have proven to be obtainable when coating the fibers with aluminum. Finally, timing resolutions of the order of 500 ps have been achieved for m.i.p. (single layer configuration), resolutions that become better for multi hit events (multilayer configuration). A comparison between the detector performances for m.i.p. and highly ionizing particle (stopped muons) will also be given, showing the possibility of particle identification based on the large difference of the energy deposit on the scintillator by the two particles. Finally results as beam monitoring tool will be shown, with measurements performed along the Paul Scherrer Institute beam lines, which provide the most intense continuous muon beam in the world. All measurements have been supported with a Monte Carlo simulation based on Geant4 and a custom code, describing the response of the SiPMs.

Paul Scherrer Institute