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/c2. It investigates the kinematics of β-particles from tritium β-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.

Highlights

  • The discovery of neutrino oscillations [1,2] and the accompanying fact of neutrino mass have made the determination of the absolute neutrino mass scale an important measurement in physics

  • The KArlsruhe TRItium Neutrino experiment (KATRIN) is a next-generation experiment based on the same technique, which aims to determine the effective mass of the electron antineutrino with a sensitivity of 0.2 eV/c2 (90% C.L.) [8]

  • Using an electromagnetic configuration in which electrons are directly guided from the surface of the main spectrometer (MS) to the focal-plane detector (FPD), rate correlations with the muon detector system indicate that 12.3 ± 1.2% of the observed rate from the MS surface is muon-induced

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Summary

Introduction

The discovery of neutrino oscillations [1,2] and the accompanying fact of neutrino mass have made the determination of the absolute neutrino mass scale an important measurement in physics. Using this distribution, a very simple Geant simulation [14,15,16] was performed to estimate the flux of muons through the KATRIN main spectrometer, resulting in a total rate of 45000 μ/s. A very simple Geant simulation [14,15,16] was performed to estimate the flux of muons through the KATRIN main spectrometer, resulting in a total rate of 45000 μ/s These muons produce secondary electrons as they make two crossings of the inner surface of the stainless steel vessel. If muons contribute to the background, a surplus of secondary electrons is expected in the time window following a signal from the muon detectors This method fails if muoninduced secondaries are trapped in the spectrometer for a significant time before being detected.

Measurement apparatus
Main spectrometer and focal-plane detector
Muon detector system
Measurements
Validation of muon-induced background mechanism
Coincidence analysis
Comparison with simulation
Correlation of cosmic-ray muon rate with detected background
Muon coincidence under nominal conditions
Correlation under asymmetric magnetic field conditions
Electron production rate from muons
Residual muon-induced background with symmetric magnetic field
Findings
Conclusion
Full Text
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