The Super Fine-Grained Detector for the T2K neutrino oscillation experiment

TL;DR

The SuperFGD is a highly segmented, optically isolated plastic scintillator detector that enhances neutrino interaction detection, particle identification, and neutron reconstruction, significantly improving the T2K experiment's measurement precision.

Contribution

This paper introduces the novel SuperFGD detector with 2 million scintillator cubes, enabling detailed 3D imaging, neutron detection, and precise timing for the first time in a neutrino experiment.

Findings

Successful installation and commissioning in 2023

Enhanced particle identification and neutron energy reconstruction

Improved detector response characterization with recent data

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.