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Description
Long scintillation strips with embedded WLS fibers are widely used in muon systems of modern experimental facilities, including future electron-positron colliders. To accurately reconstruct particle tracks and to simulate the passage of particles through the strips of the muon system, it is necessary to know the parameters of the scintillators with high accuracy: light output, attenuation length, and light propagation in the scintillator and in the WLS fiber.
We present results of test measurements and simulation of scintillator strips with WLS fiber readout. Extruded rectangular and triangle cross section strips with holes in the center along the strips and rectangular cross section strips with grooves on the surface were used for the tests. Light from the scintillators was collected using WLS fibers.
The aim of the measurements was to determine the distance from which scintillation light is captured by the WLS fiber and the distribution of captured photons along the fiber after passage of a charged particle.
Two approaches were used for the measurements. In the first, a 50-cm-long WLS fiber was embedded into a hole in the extruded strip of approximately 75 cm long so that its far end was located in the middle of the strip. In the second approach, the fiber used for measurements was completely dyed black, except for a short 15 mm long section. The signals were registered from the fibers using a PMT or SiPM, the far ends of the fibers were blackened. A collimated strontium beta source was employed to ionize the strips. The beta source moved along the strip towards the photosensor, starting its movement far from the end of the WLS fiber. In the first case, the signal from the photosensor begins to increase as the source approaches the fiber and reaches 50% of the maximum value when the source is at the edge of the fiber. As the source moves further, the signal increases and reaches its maximum. In the second approach, the signal peak was observed when the beta source was located above the center of the open part of the fiber. In this case, the width of the signal amplitude distribution at half-maximum is about 35 mm. The measured distributions are in good agreement with the simulation results obtained using Geant 4.
