Calibration Of Light Response For The Nexo Neutrinoless Double Beta Decay Search With Machine Learning
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Calibration of Light Response for the NEXO Neutrinoless Double Beta Decay Search with Machine Learning
Neutrinoless double beta decay (0[nu][beta][beta]) is a rare second-order process that, if observed, would confirm that neutrinos are Majorana fermions. This process violates the conservation of lepton number and hence would provide yet another indication of physics beyond the Standard Model (SM). EXO-200 was an experiment aiming to detect 0[nu][beta][beta], and nEXO is the next generation experiment proposed as a successor to EXO-200 using enriched 136Xe in a time projection chamber. It is projected that nEXO will reach a sensitivity of 1.35×1028yr to the 0[nu][beta][beta] half life of 136Xe with 10 years of data taking. nEXO uses silicon photomultipliers (SiPMs) for light detection. Calibration of SiPMs is very important to meet the energy resolution requirement of
Radon Injection for Light Response Calibration of the NEXO Detector
Neutrinoless double beta decay (0vbb) is a second-order process that occurs in isotopes for which single beta decay is energetically forbidden. Observation of 0vbb would demonstrate that the neutrino is a Majorana particle and would violate total lepton number conservation. The nEXO experiment will search for 0vbb of 136-Xe using 5 tonnes of enriched liquid xenon in a low-background single-phase time projection chamber. nEXO is expected to reach a 10 year sensitivity to the 0vbb halflife of 136-Xe of approximately 10^28 years. This dissertation presents a novel technique for calibrating the response of the nEXO detector to scintillation signals using an injection of radon into the xenon recirculation loop. The baseline calibration plan for nEXO is a series of external gamma-ray sources which suffer from xenon's self-shielding properties. Dissolved calibration sources, on the other hand, are capable of characterizing the center of nEXO's large drift chamber, especially when complemented by liquid xenon fluid simulations. Better characterization of the detector response to light improves the energy resolution of the detector and therefore its sensitivity to the halflife of 0vbb. I present results from an end-of run calibration campaign on nEXO's predecessor experiment, EXO-200, using two candidate isotopes: 220-Rn and 222-Rn. I report observed alpha populations, efficiency corrections, and validation of EXO-200 fluid simulations using these data. This work also presents a new framework that combines fluid simulations with nEXO Monte Carlo to produce position-dependent functions of the detector response to light. Finally, I propose possible calibration schemes for radon injection for the nEXO detector.
Search for Neutrinoless Double Beta Decay with EXO-200 and NEXO
Neutrinoless Double Beta Decay is a theorized nuclear decay in which a nucleus decays via the emission of two electrons but no neutrinos. Detection of this lepton number violating process represents the best test of the Majorana nature of neutrinos, which could potentially provide an elegant mechanism by which neutrinos obtain mass. Both the recently decommissioned EXO-200 and the future experiment nEXO search for this hypothesized decay using liquid xenon time projection chambers filled with xenon enriched in the isotope Xe136. In the first part of this work, the results from the final neutrinoless double beta decay search of EXO-200 with the complete dataset is presented. This includes a description of the advanced analysis techniques used to maximize the topological discrimination between double beta signal and gamma backgrounds. The second part of this work presents the current state of R\& D efforts towards designing the planned tonne scale experiment, with focus on the characterization of charge-detecting tiles which are proposed to make up the anode plane of nEXO.