Scintillator ageing of the T2K near detectors from 2010 to 2021

TL;DR

This study analyzes the long-term degradation of plastic scintillators in the T2K near detectors over a decade, finding a gradual decrease in light yield that remains within operational thresholds through 2040, primarily due to scintillator ageing.

Contribution

It provides the first detailed long-term measurement of scintillator ageing in a neutrino experiment and demonstrates that the detectors will remain functional for future physics runs.

Findings

Light yield degrades by 0.9-2.2% annually

Degradation primarily due to scintillator ageing

Detectors remain operational until at least 2040

Abstract

The T2K experiment widely uses plastic scintillator as a target for neutrino interactions and an active medium for the measurement of charged particles produced in neutrino interactions at its near detector complex. Over 10 years of operation the measured light yield recorded by the scintillator based subsystems has been observed to degrade by 0.9--2.2\% per year. Extrapolation of the degradation rate through to 2040 indicates the recorded light yield should remain above the lower threshold used by the current reconstruction algorithms for all subsystems. This will allow the near detectors to continue contributing to important physics measurements during the T2K-II and Hyper-Kamiokande eras. Additionally, work to disentangle the degradation of the plastic scintillator and wavelength shifting fibres shows that the reduction in light yield can be attributed to the ageing of the plastic scintillator.