Development of cosmic-ray tracker for KASKA neutrino oscillation experiment

A cosmic-ray tracking system to trace the cosmic muon passage will be installed in the detector for the planned reactor-neutrino oscillation experiment KASKA. Background events due to isotopes produced in the spallation reaction by the cosmic muons can be estimated by their association to the cosmic-ray track. For this detector, we propose a scheme of a cosmic-ray tracker consisting of extruded plastic scintillators with wavelength-shifting fiber readout. It aims at an improvement of position uniformity, detection efficiency, and detection accuracy by using the time difference between both sides of scintillator bar. Some basic performances of prototype detector were measured by beam test at the 12-GeV Proton Synchrotron in High Energy Accelerator Research Organization (KEK).