Development of an Organic Plastic Scintillator based Muon Veto Operating at Sub-Kelvin Temperatures for the NUCLEUS Experiment

TL;DR

This paper reports the first successful operation and testing of an organic plastic scintillator-based muon veto at sub-Kelvin temperatures, crucial for reducing backgrounds in cryogenic neutrino detection experiments.

Contribution

It introduces a novel cryogenic muon veto using plastic scintillators operating at sub-Kelvin temperatures, with verified scintillation functionality and a prototype design.

Findings

Confirmed scintillation process at sub-Kelvin temperatures

Developed a disc-shaped scintillator with wavelength shifting fibers and SiPMs

First operation of a cryogenic muon veto at sub-Kelvin temperatures

Abstract

The NUCLEUS experiment aims at measuring the coherent elastic scattering of nuclear reactor antineutrinos off nuclei using cryogenic calorimeters. Operating at an overburden of 3m.w.e., muon-induced backgrounds are expected to be dominant. It is therefore essential to develop an efficient muon veto, with a detection efficiency of more than 99%. This will be realized in NUCLEUS through a compact cube assembly of plastic scintillator panels. In order to prevent a large unshielded area where the cryostat intersects the shielding arrangement without unnecessarily increasing the induced detector dead time, a novel concept has been investigated, featuring a plastic scintillator based active muon veto operating inside the NUCLEUS cryostat at sub-Kelvin temperatures. The verification of the key physical aspects of this cryogenic muon veto detector led to the first reported measurements of organic plastic scintillators at sub-Kelvin temperatures. The functionality of the principal scintillation process of organic plastic scintillators at these temperatures has been confirmed. On the basis of these findings, a disc-shape plastic scintillator equipped with wavelength shifting fibers and a silicon photomultiplier to guide and detect the scintillation light has been developed. The NUCLEUS cryogenic muon veto will be the first of its kind to be operated at sub-Kelvin temperatures.