The T2K Near Detector Upgrade
November 26, 2022
The T2K, "Tokai to Kamioka", experiment is a long baseline neutrino oscillation experiment located in Japan and dedicated to the measurements of neutrino oscillations parameters. The muon neutrino beam produced at the Japan Proton Accelerator Research Complex is measured first by a set of near detectors, and then, after 295 km, by a far water Cherenkov Super-Kamiokande detector, where the appearance of electron neutrinos in a muon neutrino beam was observed for the first time. The near detector complex is represented by the Interactive Neutrino GRID on-axis detector, designed to control the position and stability of the incoming neutrino beam, and the ND280, magnetized off-axis near detector situated at 280 meters from the neutrino production target. The main purpose of ND280 is to measure and constrain the neutrino flux before oscillations. The current focus of the T2K experiment includes measuring Charge-Parity violation in the lepton sector and improving the current knowledge of neutrino cross-section models. Such goals can be reached by increasing the statistics and reducing systematic uncertainties. Thus, the T2K upgrade program proposes rising in the beam power and modernization of the ND280 near detector. The upgrade includes replacing the $\pi^0$ detector with a 3D plastic scintillator fine-grained Super-FGD detector target that will improve hadron reconstruction, and it will be sandwiched between two Time Projection Chambers, allowing high-angle outgoing charged particles to be reconstructed. In addition, the entire structure will be covered with six Time Of Flight planes, which will reduce the background from the interactions outside of the Super-FGD. The performance of each detector upgrade module was tested separately and it was shown that the Super-FGD can reach $\sim$1 ns time resolution and perform proton and neutron reconstruction. The spatial and energy ionization loss resolution of the High-Angle Time Projection Chamber prototype does not exceed 0.8 mm and 10% respectively and Time Of Flight planes can provide 0.14 ns time resolution. In addition, the ND280 physics studies show a promising reduction of neutrino interaction model uncertainties by employing the transverse kinematic variables for current and future ND280 configurations and statistics.
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