PROSPECT scintillator analysis via quantitative NMR and simulations of HFIR background

Nicholas James Craft

doi:10.17918/00011058

As a component of the Standard Model, neutrinos provide valuable insight into key areas of particle physics. By further studying the properties of neutrinos and their interaction mechanisms, existing evaluations of neutrino characteristics can be improved, and possibilities of new physics outside the Standard Model can be explored. The Precision Oscillation and Spectrum (PROSPECT) Collaboration have successfully observed various phenomena in the realm of neutrino physics in collaboration with the High-Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. One goal of PROSPECT, like many other nuclear reactor detector experiments, is to explore the 'reactor antineutrino flux anomaly', a phenomenon where the observed, experimental flux of electron antineutrinos from nuclear reactors is approximately 6% lower than what is predicted by neutrino interaction simulations. Resolution of this discrepancy could indicate that particles (and physics in general) that exist beyond the Standard Model are at play. A precise evaluation of the antineutrino reactor flux is essential for determining background contribution to experiments detecting Coherent Elastic Neutrino-Nucleus Scattering (CEvNS), and the value of this flux depends on the hydrogen density of the liquid scintillator used. This thesis explores both the CEvNS-energy range background contribution at HFIR and the hydrogen density of the PROSPECT scintillator. Evaluations of the hydrogen content of standards relative to each other yield a concentration with an error of about~18% (well above the accepted 1%). The hydrogen density of the scintillator is found to be 6.575 ∗10²² H/g using the data from Sample 1, and 5.735 ∗10²² H/g from Sample 2, with the discrepancy possibly attributed to the evaporation of HMDSO during sample preparation. Additionally, contribution to the background at HFIR is evaluated in the energy range of likely CE[nu]NS interactions. Simulations of the PROSPECT detector in close proximity to an antineutrino flux source like HFIR reveal the particles produced via ionising reactions, quantifying the background contribution to the signal detected near HFIR. The main contributions to background signal are found to be electrons, protons, carbon-12 (¹²C), and Helium-4 (⁴He), though ⁴He atoms do not have any contribution below 10 keV (the defined energy cutoﬀ for CE[nu]NS interactions). Contributions to the background in the CE[nu]NS energy range are evaluated to be on the scale of 10⁵ dru for electrons and~10⁴ dru for protons and ¹²C, detailed in Table 4.

PROSPECT scintillator analysis via quantitative NMR and simulations of HFIR background

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PROSPECT scintillator analysis via quantitative NMR and simulations of HFIR background

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