Doctoral Dissertations

Date of Award

5-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Yuri V. Efremenko

Committee Members

Jason P. Hayward, Yuri A. Kamyshkov, Anthony Mezzacappa, W. Raphael Hix

Abstract

The COHERENT Collaboration is an experimental effort to make the first measurement of coherent elastic neutrino-nucleus scattering (CE𝜈NS). The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory provides an intense, timed source of neutrinos from the decay of pions and muons produced during the spallation of mercury by 1 GeV protons generated in a particle accelerator. COHERENT seeks to make an unambiguous measurement by using a variety of low-threshold detectors capable of measuring the low-energy nuclear recoils resulting from CE𝜈NS interactions. This already challenging task is further complicated with the presence of backgrounds. Consequently, we must seek to reduce and understand our backgrounds as well as possible. A background measurement campaign of dedicated detectors has been deployed to study these backgrounds at the SNS. One such background is inelastic neutrino-nucleus neutron production, which produces nuclear recoils of similar energy and time structure as CE𝜈NS events. Inelastic neutrino-nucleus interactions are not well studied, and neutrino-induced neutron production has yet to be measured. Cross-sections predicted from nuclear theory are computationally impossible to be calculated exactly for large nuclei and differ by as much as 30% between different models. The cross-section for neutrino-induced neutrons for large nuclei such as lead, an element commonly used in shielding material, is predicted to be comparable to the cross-section for CE𝜈NS. In addition to complimenting the detection of CE𝜈NS, this measurement is of interest to nuclear theory, supernova neutrino interactions and detection, and understanding backgrounds for all neutrino experiments at the SNS. Currently there are two detector modules containing lead and iron targets located 20 meters from the SNS neutrino source equipped with liquid scintillator cells for the detection of neutrino induced neutrons.

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