Muon-induced background in the KATRIN main spectrometer

TL;DR

The paper investigates muon-induced backgrounds in the KATRIN main spectrometer, demonstrating that cosmic-ray muons contribute less than 17% to the overall background due to effective shielding.

Contribution

It provides a detailed measurement and model of muon-induced secondary electron production in the KATRIN spectrometer, quantifying muon contribution to background levels.

Findings

Muon-induced secondary electrons are about 12% of inner surface emissions.

Approximately one secondary electron is produced per 17 muon crossings.

Muons contribute less than 17% to the total background at 90% confidence level.

Abstract

The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to make a model-independent determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c$^{2}$. It investigates the kinematics of $\beta$-particles from tritium $\beta$-decay close to the endpoint of the energy spectrum. Because the KATRIN main spectrometer (MS) is located above ground, muon-induced backgrounds are of particular concern. Coincidence measurements with the MS and a scintillator-based muon detector system confirmed the model of secondary electron production by cosmic-ray muons inside the MS. Correlation measurements with the same setup showed that about $12\%$ of secondary electrons emitted from the inner surface are induced by cosmic-ray muons, with approximately one secondary electron produced for every 17 muon crossings. However, the magnetic and electrostatic shielding of the MS is able to efficiently suppress these electrons, and we find that muons are responsible for less than $17\%$ ($90\%$ confidence level) of the overall MS background.