Development of a neutrino detector and electronics for precise measurement of neutrino cross-section ratios

The J-PARC T59 experiment, named WAGASCI, has been developing a neutrino detector to measure a cross section ratio of charged current interaction on nucleus between water and plastic targets with uncertainties of a few percent at the J-PARC neutrino beamline. The WAGASCI detector adopts three-dimensional grid structure of 3mm-thick plastic scintillator bars around water target, to perform three-dimensional reconstruction of a particle trajectory, to improve the acceptance for large angle tracks. The light from scintillator is read out by MPPCs. An array of 32-channel MPPCs has been newly developed for this experiment. The total number of channels for the WAGASCI detector is 1280. The SPIROC2D ASIC chip, developed by OMEGA, has been employed in the frontend electronics. SPIROC2D is an auto-triggered, bi-gain, 36-channel ASIC, allowing the measurement of the charge from one to 2000 photoelectrons and the time with 100ps resolution. It contains a 16-deep analog memory array, which allows 16 hits to be stored in an acquisition gate. The backend electronics utilize Spartan6 FPGAs. The system to synchronize the data acquisition to the beam timing from J-PARC has been also developed and the data acquisition system has also been developed. The data taking with neutrino beam has started since autumn October 16, 2017.