Design and characterization of a photosensor system for the RELICS experiment

TL;DR

This paper presents a novel photosensor system with extended dynamic range for the RELICS experiment, enabling detection of neutrino signals amidst cosmic backgrounds by mitigating PMT saturation.

Contribution

The development of a dual readout photosensor system with extended linear response range for PMTs in the RELICS experiment is a key innovation.

Findings

Extended PMT linear response by over an order of magnitude.

System successfully detects neutrino signals under cosmic backgrounds.

Model of PMT saturation and recovery supports system design.

Abstract

In this paper, we present the design and characterization of a photosensor system developed for the RELICS experiment. An extended dynamic range base was designed to mitigate photomultiplier tube (PMT) saturation caused by intense cosmic muon backgrounds in the surface-level RELICS detector. The system employs dual readout from the anode and the seventh dynode to extend the linear response range of the PMT. In particular, our characterization and measurements of Hamamatsu R8520-406 PMTs confirm stable operation under positive high-voltage bias, extending the linear response range by more than an order of magnitude. Furthermore, a model of PMT saturation and recovery was developed to evaluate the influence of cosmic muon signals in the RELICS detector. The results demonstrate the system capability to detect coherent elastic neutrino-nucleus scattering signals under surface-level cosmic backgrounds, and suggest the potential to extend the scientific reach of RELICS to MeV-scale interactions.