Investigation of Background from the Inter-Spectrometer Penning Trap and Secondary Electron Emission in the KATRIN Experiment

Thesis (Ph.D.)--University of Washington, 2019The KATRIN experiment aims to determine the neutrino mass with unprecedented precision by measuring the tritium $\beta$-decay spectrum with a tandem of MAC-E-filter spectrometers. The background rate measured at the $\beta$-detector is a crucial parameter affecting the sensitivity of the experiment. The detector energy resolution affects the intrinsic background contribution from the detector system and, therefore, must be well-characterized. Additionally, the increased size of the main spectrometer compared with predecessor experiments necessitates understanding and quantifying various sources of background electrons originating from the spectrometer. Secondary electron emission from the inner spectrometer surface, induced by environmental gamma radiation and cosmic-ray muons, is investigated as a potentially large source of background electrons. A background source unique to the beamline geometry of KATRIN is the inter-spectrometer Penning trap formed during tandem operation of the spectrometers. Detailed measurements and simulations were performed to quantify the background induced by the Penning trap and to confirm the electron-production model. However, by maintaining ultra-high vacuum conditions inside the spectrometers, the effect of the trap on the total background rate is found to be insignificant compared with contributions from other sources

First operation of the KATRIN experiment with tritium

The determination of the neutrino mass is one of the major challenges in astroparticle physics today. Direct neutrino mass experiments, based solely on the kinematics of β β -decay, provide a largely model-independent probe to the neutrino mass scale. The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to directly measure the effective electron antineutrino mass with a sensitivity of 0.2 eV 0.2 eV (90% 90% CL). In this work we report on the first operation of KATRIN with tritium which took place in 2018. During this commissioning phase of the tritium circulation system, excellent agreement of the theoretical prediction with the recorded spectra was found and stable conditions over a time period of 13 days could be established. These results are an essential prerequisite for the subsequent neutrino mass measurements with KATRIN in 2019

Quantitative Long-Term Monitoring of the Circulating Gases in the KATRIN Experiment Using Raman Spectroscopy.

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims at measuring the effective electron neutrino mass with a sensitivity of 0.2 eV/c2, i.e., improving on previous measurements by an order of magnitude. Neutrino mass data taking with KATRIN commenced in early 2019, and after only a few weeks of data recording, analysis of these data showed the success of KATRIN, improving on the known neutrino mass limit by a factor of about two. This success very much could be ascribed to the fact that most of the system components met, or even surpassed, the required specifications during long-term operation. Here, we report on the performance of the laser Raman (LARA) monitoring system which provides continuous high-precision information on the gas composition injected into the experiment's windowless gaseous tritium source (WGTS), specifically on its isotopic purity of tritium-one of the key parameters required in the derivation of the electron neutrino mass. The concentrations cx for all six hydrogen isotopologues were monitored simultaneously, with a measurement precision for individual components of the order 10-3 or better throughout the complete KATRIN data taking campaigns to date. From these, the tritium purity, εT, is derived with precision of <10-3 and trueness of <3 × 10-3, being within and surpassing the actual requirements for KATRIN, respectively

Quantitative Long-Term Monitoring of the Circulating Gases in the KATRIN Experiment Using Raman Spectroscopy.

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims at measuring the effective electron neutrino mass with a sensitivity of 0.2 eV/c2, i.e., improving on previous measurements by an order of magnitude. Neutrino mass data taking with KATRIN commenced in early 2019, and after only a few weeks of data recording, analysis of these data showed the success of KATRIN, improving on the known neutrino mass limit by a factor of about two. This success very much could be ascribed to the fact that most of the system components met, or even surpassed, the required specifications during long-term operation. Here, we report on the performance of the laser Raman (LARA) monitoring system which provides continuous high-precision information on the gas composition injected into the experiment's windowless gaseous tritium source (WGTS), specifically on its isotopic purity of tritium-one of the key parameters required in the derivation of the electron neutrino mass. The concentrations cx for all six hydrogen isotopologues were monitored simultaneously, with a measurement precision for individual components of the order 10-3 or better throughout the complete KATRIN data taking campaigns to date. From these, the tritium purity, εT, is derived with precision of <10-3 and trueness of <3 × 10-3, being within and surpassing the actual requirements for KATRIN, respectively