A Study of the Muon Veto and Cosmogenic Neutron Background for the Scintillating Bubble Chamber Dark Matter Experiment

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Hatch, Patrick
dark matter , direct dark matter detection , low background experiments
Dark matter is one of the most intriguing and elusive physics topics in recent decades with many dark matter candidates proposed and many experiments designed to search for these candidates. One category of candidates known as low-mass WIMPs is becoming of interest to the dark matter community with numerious experiments attempting to reach very low energy thresholds to search for these particles. The Scintillating Bubble Chamber (SBC) is one such experiment. The SBC is a bubble chamber using a scintillating target fluid allowing it to reach lower energy thresholds than previous bubble chamber experiments. This thesis investigates one major background for the experiment: cosmogenic neutrons, sometimes called muon-induced neutrons. This background can be mitigated using a muon veto consisting of a water shield surrounding the SBC with photomultipler tubes (PMTs) mounted inside to capture muon produced Cerenkov light. The first part of this thesis' research tested various muon veto design and found that adding reflectivity to the inner walls of the water shield is crucial to achieve 99\% veto efficiency. The second part of this thesis' research counted the number of expected bubble events produced by cosmogenic neutrons and found that adding a water shield significantly dropped the number of events from 0.152 events per year to 0.076 events per year. All this work is done using Monto Carlo simulations within the particle physics simulation software Geant4.
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