Development of proton beam irradiation system for the NA65/DsTau experiment

Tau neutrino is the least studied lepton of the Standard Model (SM). The NA65/DsTau experiment targets to investigate D_s, the parent particle of the ν_τ, using the nuclear emulsion-based detector and to decrease the systematic uncertainty of ν_τ flux prediction from over 50 future beam dump experiments. In the experiment, the emulsion detectors are exposed to the CERN SPS 400 GeV proton beam. To provide optimal conditions for the reconstruction of interactions, the protons are required to be uniformly distributed over the detector's surface with an average density of 10^5 cm^-2 and the fluctuation of less than 10 issue, we developed a new proton irradiation system called the target mover. The new target mover provided irradiation with a proton density of 0.98 cm^-2 and the density fluctuation of 2.0± 0.3 2021 run.