High-granularity timing hodoscopes for the AMBER experiment

The AMBER experiment at CERN will measure the proton's charge radius via muon-proton elastic scattering at high projectile energies and small momentum transfers to help to resolve the so-called proton radius puzzle, i.e., the discrepancy between charge radii measured with different experimental techniques. The core setup at AMBER consists of a hydrogen-filled time projection chamber (TPC). Tracking detectors upstream and downstream of the TPC measure the trajectories of the incoming and outgoing muons to determine their scattering angles. To resolve pile-up hits in the tracking detectors, we are constructing four high-granularity hodoscopes from 500-μm scintillating-plastic fibers and arrays of silicon photomultipliers. In this contribution, we present the design of the scintillating-fiber hodoscopes and first results of test-beam measurements with scaled-down prototypes. We will particularly emphasize how we managed to design detectors with a low material budget.