[論文レビュー] The Super Fine-Grained Detector for the T2K neutrino oscillation experiment

S. Abe, H. Alarakia-Charles+170 more|arXiv (Cornell University)|Mar 16, 2026

Neutrino Physics Research被引用数 0

ひとこと要約

要約: The paper describes the design, construction, and commissioning of the SuperFGD, a 3D-segmented 1 cm3 scintillator cube detector with WLS fibres and MPPC readout for the T2K ND280 upgrade, enabling isotropic tracking and neutron energy reconstruction.

ABSTRACT

The magnetised near detector ND280 of the long-baseline neutrino experiment T2K has been upgraded to improve its detection performance and, consequently, enhance our understanding of neutrino-nucleus interactions, reducing the systematic uncertainties in measurements of the neutrino oscillation parameters. A key component of the upgrade is a novel segmented plastic scintillator detector, called the Super Fine-Grained Detector (SuperFGD), made of approximately 2 million optically isolated 1 cm$^3$ cubes read out by three orthogonal wavelength-shifting (WLS) fibres. Scintillation photons are detected by 55,888 Hamamatsu Multi-Pixel Photon Counters (MPPCs). The SuperFGD provides 3D images of neutrino interactions by tracking the final-state charged particles produced isotropically, including protons down to a threshold of around 330 MeV/$c$. The high light yield of SuperFGD greatly improves particle identification and the sub-nanosecond time resolution provides an excellent identification of Michel electrons. The SuperFGD is also able to detect neutrons from neutrino interactions and, for the first time in a neutrino experiment, to reconstruct their kinetic energy using a fine detector segmentation and by measuring the time-of-flight with sub-nanosecond precision. In this article the details of the detector design, construction and performance are described. The detector was installed in ND280 and successfully commissioned with cosmic data in 2023 and, later, with the T2K neutrino beam. The detector response has been characterised with the 2023 and 2024 data and the results are reported in this article.

研究の動機と目的

• Improve near-detector performance for T2K by enabling full angular acceptance and improved tracking of low-momentum particles.
• Enable detection and kinetic-energy reconstruction of neutrons from neutrino interactions.
• Achieve high light yield and sub-nanosecond timing for Michel electron identification and proton/pion discrimination.
• Provide a homogeneous plastic-scintillator target with enhanced efficiency compared to previous ND280 detectors.

提案手法

• Use ~2 million 1 cm3 scintillator cubes arranged in a 56-layer, 192×182 cube array to form a 3D detector.
• Read out light from each cube via three orthogonal wavelength-shifting fibres connected to MPPCs (55,888 channels).
• Ship and assemble cubes with precise hole geometry and optical guidance to ensure reliable fibre coupling and minimal stress on fibres.
• Incorporate an LED calibration system and a dedicated electronics architecture for synchronization, timing, and data acquisition.

Figure 1 : The T2K near detector ND280 before the upgrade (left). The PØD is replaced by new detectors HA-TPCs, SuperFGD, and ToF after the upgrade (right).

実験結果

リサーチクエスチョン

• RQ1 Can the SuperFGD provide isotropic tracking with high efficiency for low-momentum protons and pions across all polar angles?
• RQ2 Can the detector reconstruct neutron kinetic energy via time-of-flight with fine segmentation?
• RQ3 What is the achievable light yield, time resolution, and particle identification performance with the cube-based design?
• RQ4 How does the mechanical box design ensure stable cube alignment and reliable fibre coupling under operational conditions?

主な発見

• The SuperFGD contains 1,956,864 cubes read out by 55,888 channels, providing 3D tracking with isotropic acceptance.
• The design enables proton thresholds down to about 330 MeV/c and neutron energy reconstruction via time-of-flight with sub-nanosecond timing.
• The detection system demonstrated successful commissioning with cosmic data in 2023 and with the T2K beam later in 2023–2024.
• The mechanical box and assembly procedures achieved alignment tolerances that ensure reliable WLS fibre coupling and overall structural stability under expected conditions.

Figure 2 : Left: A zoom view a scintillator cube with three orthogonal holes with a diameter of 1.5 mm. Two sides of the cube polished to see the holes, four sides a covered by a reflector. Right: Scintillator cubes before and after chemical etching. A trace from the injection mould pusher is seen a