A flow-based model for electronegative impurity transport in EXO-200

An observation of neutrinoless double beta decay, a hypothetical second-order weak interaction, may reveal the Dirac/Majorana nature of the neutrinos and demonstrate lepton number violation. The EXO-200 experiment was designed to search for neutrinoless double beta decay using an ultra-low background single-phase time projection chamber. The detector contains 110~kg of active liquid xenon, isotopically enriched in Xe-136, which acts as both the decaying nucleus and detection medium. To optimize the signal of such a detector, the liquid xenon needs to be kept free of electronegative impurities which could interact with drifting electron signals and reduce energy resolution. This study investigates whether fitting the ionization signals from the two time projection chamber halves separately or combining the datasets for fitting yields a more accurate purity correction. The latter method was found to improve the purity correction on the EXO-200 data and has been implemented in the EXO-200 standard analysis pipeline. Using the combined dataset, a purification model and its modifications have been developed and tested. The purification model utilizes the physical parameters measured in the detector and can improve the understanding of purity behavior in the detector, while providing detector measurements. The fitting performance of the 2-Phase Model to EXO-200 electron lifetime data is shown to be comparable to that of the polynomial function method. In addition, the 2-Phase Model can adapt to changes in the system and does not require human input, thus eliminating any inconsistency in the purity correction for the ionization energy in the physics data.Ph.D., Physics -- Drexel University, 201