The neutrino monitor building on the J-PARC site is located about 280 m downstream of the neutrino production target. Several detectors are installed inside a vertical shaft, which has a diameter of 17.5 m and a depth of 33.5 m. At the beam center, there is an “on-axis detector” known as INGRID. This detector consists of 14 modules arranged in a cross shape, and monitors the direction and intensity of the neutrino beam. The “off-axis detectors”, not at the beam center direction, include the ND280 placed in the direction of SK (2.5°), and another detector called WAGASCI/BabyMIND placed at the 1.5° direction. Utilizing the ND280, we measure the energy distribution of the generated neutrinos and the electron neutrino component in the beam. Moreover, utilizing three near detectors with different energy ranges and target material, we study neutrino interactions in detail.

ND280 upgrade

The T2K group has conducted the upgrade of the ND280 detector. A part of the original ND280 has been replaced with new types of detectors, such as the Super-Fine-Grained detector (SuperFGD), a Time Projection Chamber (HA-TPC), and a Time-of-Flight (TOF) detector. We aim to conduct more detailed measurements of neutrino interactions with the upgraded detectors. The KEK/J-PARC neutrino group, in collaboration with researchers from both international and domestic institutions, constructed and installed the SuperFGD. The SuperFGD, which consists of two million of 1 cm³ scintillator cubes, can measure the 3D trajectories of charged particles from neutrino interactions. It enables us to measure the neutrino interactions in detail.