Scintillating microfibers as a high-resolution tracking detector for hybrid-emulsion experiment

We have developed a very thin and high precision tracking detector using a coherent bundle of plastic scintillating microfibers for an emulsion-counter hybrid experiment to search for double-strangeness nuclei. The purpose of this detector is to measure the position and angle of short-lived particles, such as low-momentum Ξ− particles produced in (K−, K+) reactions. The dependence of the light yield and attenuation length of fibers on the density of the wavelength shifter and the fiber diameter have been studied. A test experiment with a prototype fiber detector and emulsion has been carried out using 0.5 GeV/c protons. The tracks tagged by the fiber detector were identified in the emulsion. By comparing the position and the angle of tracks predicted by the detector with the measurements of the tagged tracks in the emulsion, positions were determined with an r.m.s precision of 113 μm and angles were determined with an r.m.s precision of 25 mrad with a very thin detector of about 4 mm thickness.