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The Main Electrode System of the Nab Experiment and the Analysis of the Performance in the Measurement of the Fierz Term b

Published 21 Feb 2024 in physics.ins-det and nucl-ex | (2402.13559v1)

Abstract: The Nab collaboration will study free neutron beta decay at the Spallation Neutron Source at Oak Ridge National Lab. A neutron decays into a proton, an electron and an anti-neutrino in this process, where the energy of the outgoing protons and electrons are collected to determine (1) the electron-antineutrino correlation co-efficient aa to the precision of |Δa/a\Delta a/a|<=10<sup>−310<sup>{-3} and (2) the Fierz interference term bb to the precision of |Δb/b\Delta b/b|<=3∗10<sup>−33*10<sup>{-3}. From the measurement of aa, we can calculate the axial-vector to vector coupling ratio λ\lambda. Together with the neutron lifetime measurement, we could also calculate the upper right element of the Cabbibo-Kobayashi-Maskawa Matrix, and test the unitarity of that matrix. The measurement of bb could shed light on the physics beyond the Standard Model since bb is predicted to be 0 by the V−AV-A structure of weak interaction in the Standard Model. This thesis presents the design of Nab electrode system, and the solution to a major systematic effect in the measurement of aa: the requirement of having a low electrical field environment in the neutron decay region. The electrode system has been built and installed successfully, and as our characterization and its analysis shows, the electrode system meets the required specifications. This thesis also gives a systematic uncertainty study for bb measurement and provides a table of the requirements for the bb measurement...

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