Background, calibration, and validation simulations for SBC dark matter and reactor CEvNS experiments

Noah R. Lamb

doi:10.17918/00011165

The Scintillating Bubble Chamber (SBC) Collaboration plans to use liquid noble bubble chambers in rare event searches such as nuclear recoils from dark matter and neutrino scattering. Bubble chambers are particle detectors that use liquid above its boiling point in a "superheated" state in order to detect particle interactions. When a particle deposits energy inside the detector, the liquid boils, and a bubble forms. Liquid noble bubble chambers have unique potential as a scalable, low-background, low-energy nuclear recoil detector. Dark matter refers to yet undetected matter that is predicted to comprise most of the mass in the universe based on astronomical observations. SBC has plans to operate reactor neutrino experiments in the future. With the goal of being sensitive to 100 eV nuclear recoils, there is considerable potential for discovery for these experiments. SBC is constructing two 10-kg liquid argon bubble chambers, one to be deployed at Fermi National Accelerator Lab (Fermilab) and the other to be deployed in the SNOLAB underground facility (an expansion of the Sudbury Neutrino Observatory). The Fermilab chamber is a full-scale prototype designed for tests and calibrations, including a novel gamma nucleus elastic scattering calibration. The calibration is required to infer a dark matter sensitivity of the detector. The chamber at SNOLAB will conduct a dark matter search deep-underground with low cosmic radiation. This thesis focuses on the gamma-ray backgrounds and calibration for the SBC experiment. This includes simulations of inner shell electron ionization and nuclear recoils from gamma-rays to understand the detection of environmental radiation and predict the rate at which this radiation is detected. These inner shell ionization simulations helped to confirm a mechanism for electronic recoil backgrounds previously observed in PICO chambers and has implications for future experiments. I developed a high statistics method for simulating nuclear recoils from gamma-rays to inform the shielding design of SBC and design a calibration plan. A simulated calibration is performed to determine the best calibration sources to use and predict the accuracy that can be achieved with a realistic calibration campaign. SBC has a target of 20% or lower uncertainty on the detector threshold for a near-term dark matter search and a target of 5% or lower uncertainty on the detector threshold for a reactor neutrino experiment. The results from the simulated calibration suggest both targets are achievable and estimate the systematic uncertainties required to meet those targets.

Background, calibration, and validation simulations for SBC dark matter and reactor CEvNS experiments

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Background, calibration, and validation simulations for SBC dark matter and reactor CEvNS experiments

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