Prospect and status of the physics run of the NINJA experiment

Abstract

Neutrino-nucleus interaction is a major source of the systematic uncertainty for neutrino oscillation experiments. The NINJA experiment aims to measure the neutrino-water interactions precisely with a nuclear emulsion detector called an Emulsion Cloud Chamber (ECC). Nuclear emulsions have sub-micron position resolution and allow us to detect short tracks of low momentum secondary charged particles such as protons. In the NINJA experiment, a muon detector is placed downstream of ECC because it cannot identify muons from $\nu_{\mu}$ charged current interactions by itself. In contrast with its good position resolution, the nuclear emulsion doesn't have timing information and enormous tracks are accumulated in the detector during the whole experiment. Therefore, the position resolution of the muon detector is not enough to connect the muon tracks to ECCs one by one. The NINJA experiment solves this problem by using a scintillator tracker between the muon detector and ECC, which has equivalent timing resolution and better position resolution. The NINJA experiment is planning a physics run with a 75~kg water target from November 2019. Since the target mass is larger than previous runs, a larger tracker covering 1 m $\times$ 1 m area is needed. In this paper, we will show the status of preparation for the physics run, especially about development of the new scintillator tracker.