The T2K Fine-Grained Detectors

TL;DR

This paper details the design, construction, and initial performance results of two fine-grained detectors used as active targets in the T2K neutrino experiment's near detector system, enhancing understanding of neutrino interactions.

Contribution

It introduces the design and construction of two novel fine-grained detectors for the T2K experiment's near detector, including their components and initial performance evaluations.

Findings

Successful construction and calibration of the FGDs

Initial performance tests show effective detection capabilities

Enhanced understanding of neutrino interactions at the near detector

Abstract

T2K is a long-baseline neutrino oscillation experiment searching for $\nu_e$ appearance in a $\nu_{\mu}$ beam. The beam is produced at the J-PARC accelerator complex in Tokai, Japan, and the neutrinos are detected by the Super-Kamiokande detector located 295 km away in Kamioka. A suite of near detectors (ND280) located 280 m downstream of the production target is used to characterize the components of the beam before they have had a chance to oscillate and to better understand various neutrino interactions on several nuclei. This paper describes the design and construction of two massive fine-grained detectors (FGDs) that serve as active targets in the ND280 tracker. One FGD is composed solely of scintillator bars while the other is partly scintillator and partly water. Each element of the FGDs is described, including the wavelength shifting fiber and Multi-Pixel Photon Counter used to collect the light signals, the readout electronics, and the calibration system. Initial tests and {\normalsize\em in situ} results of the FGDs' performance are also presented.