Measurement of oscillations in solar boron-8 neutrinos and studies of optical scattering in the SNO+ detector

SNO+ is a large-scale liquid scintillator experiment based in Sudbury, Canada, capable of probing many aspects of neutrinos. One major property of interest is the neutrino’s ability to oscillate between different flavours, an indirect demonstration that neutrinos must have mass. This thesis performs the first ever measurement of oscillations from 8B solar neutrinos in the scintillator phase of SNO+. Assuming the current global fit flux of 8 B solar neutrinos, the neutrino oscillation parameter theta_12 was measured to be 38.9 degrees +8.0-7.9 degrees, using an initial 80.6 days of data. This result is consistent with the current global fit result of 33.44 degrees +0.77-0.74 degrees. A sensitivity study indicates that the precision of this result is capable of improving by at least a factor of two within two years of livetime. On top of this, substantial improvements were made to all aspects of the optical calibration system known as SMELLIE. This is a series of optical-wavelength lasers whose light is emitted from optical fibres attached to the edge of the SNO+ detector. By developing a new analysis, this system was able to measure the scintillator extinction lengths as a function of wavelength and time in-situ for the first time. A new analysis was also built and demonstrated to observe changes in scattering and scintillator re-emission properties of the scintillator as a function of time and wavelength. Alongside this, major upgrades were made to both the hardware and simulation of the SMELLIE system, enabling higher-quality data to be taken, and simulations to be made with much greater speed

Event-by-event direction reconstruction of solar neutrinos in a high light-yield liquid scintillator

The direction of individual B8 solar neutrinos has been reconstructed using the SNO+ liquid scintillator detector. Prompt, directional Cherenkov light was separated from the slower, isotropic scintillation light using time information, and a maximum likelihood method was used to reconstruct the direction of individual scattered electrons. A clear directional signal was observed, correlated with the solar angle. The observation was aided by a period of low primary fluor concentration that resulted in a slower scintillator decay time. This is the first time that event-by-event direction reconstruction in high light-yield liquid scintillator has been demonstrated in a large-scale detector.</p

Measuring Solar Neutrinos in the SNO+ Detector

The SNO+ experiment is a large multi-purpose neutrino detector, currently filled with liquid scintillator. For the first time in a single experiment, SNO+ is able to measure the neutrino oscillation parameters $\theta_{12}$ and $\Delta m^{2}_{21}$ simultaneously through both reactor anti-neutrinos and $^{8}B$ solar neutrinos. The latter approach is demonstrated here, with an analysis of an initial 80 days of scintillator phase data. A Bayesian statistical approach via Markov Chain Monte Carlo is used, allowing for the simultaneous fitting of the oscillation parameters, $^{8}B$ neutrino flux, background components with constraints, and systematic uncertainties. The neutrino oscillation parameter $\theta_{12}$ was measured to be $38.9^{\circ+8.0^{\circ}}_{-7.9^{\circ}}$, assuming the current global fit flux of $^{8}B$ solar neutrinos. This is consistent with the current global fit result for $\theta_{12}$. A sensitivity study shows that this measurement is statistics-limited, and precision could be improved by a factor of two with two years of livetime, assuming the same backgrounds and selections.Comment: 6 pages, 4 figures; presented as a poster at NuPhys202

Optical calibration of the SNO+ detector in the water phase with deployed sources

SNO+ is a large-scale liquid scintillator experiment with the primary goal of searching for neutrinoless double beta decay, and is located approximately 2 km underground in SNOLAB, Sudbury, Canada. The detector acquired data for two years as a pure water Cherenkov detector, starting in May 2017. During this period, the optical properties of the detector were measured in situ using a deployed light diffusing sphere, with the goal of improving the detector model and the energy response systematic uncertainties. The measured parameters included the water attenuation coefficients, effective attenuation coefficients for the acrylic vessel, and the angular response of the photomultiplier tubes and their surrounding light concentrators, all across different wavelengths. The calibrated detector model was validated using a deployed tagged gamma source, which showed a 0.6% variation in energy scale across the primary target volume

Arsenate of lead as an insecticide against the tobacco hornworms /

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