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A Combined Three-Phase Signal Extraction of the Sudbury Neutrino Observatory Data Using Markov Chain Monte Carlo Technique Open Access


Other title
neutrino physics
Markov Chain Monte Carlo
Type of item
Degree grantor
University of Alberta
Author or creator
Habib, Shahnoor
Supervisor and department
Hallin, Aksel (Physics)
Examining committee member and department
Huber, Garth (Physics)
Moore, Roger (Physics)
Schmuland, Byron (Mathematics)
Freeman, Mark (Physics)
Department of Physics

Date accepted
Graduation date
Doctor of Philosophy
Degree level
\begin{Large} \truedoublespacing \begin{center} \textbf{Abstract} \end{center} Neutrino physics has entered an era of precision, after proving that the Standard Solar Model is a viable theory and going beyond the current Standard Model of particle physics by proving that neutrinos possess nonzero masses. The Sudbury Neutrino Observatory (SNO) experiment, along with other experiments, has restricted neutrino mixing angle ($\theta_{12}$) and the mass square difference ($\Delta m^{2}_{21}$) to lie within the large mixing solution area. SNO, located 2~km underground in Sudbury, Canada, was an ultraclean heavy-water (D$_2$O) imaging detector for observing neutrinos produced by fusion reactions in the Sun. Neutrino interactions with heavy water resulted in flashes of light called $\breve{\rm{C}}$erenkov radiation which was detected by an array of photomultiplier tubes. SNO took data from November 1999 to November 2006, totalling 1082 days of data taking. This work describes an improved measurement of the mixing parameters from a combined fit of all the data. For the signal extraction fit on the data consisting of 4 observable of an event -- radial position, recoil electron energy, direction relative to the Sun and event isotropy -- Markov Chain Monte Carlo (MCMC) method based on Metropolis algorithm was employed. The nuisance parameters (systematics), weighted by external constraints, were allowed to vary in the fit. The goal of the thesis was to extract the survival probabilities of electron neutrinos and determine the total flux of active-flavour neutrinos from $^{8}$B decay in the Sun measured through the neutral current interactions of neutrinos on deuterium. The $^{8}$B flux from the fit is $(5.24\pm0.02) \times 10^{6}~\mbox{cm}^{-2}~ s^{-1}$; uncertainty from statistics and systematics is 3.56$\%$. Along with $^{8}$B flux, the fit extracted energy spectra of charged current interactions of neutrinos on deuterium and elastic scattering interactions of neutrinos on electrons. The fit described the energy-dependent day survival probability of solar neutrinos as a quadratic equation and asymmetry on the day survival probability as a linear equation. Four polynomial coefficients of the survival probability were extracted from the fit: constant coefficient as $0.3206\pm0.0197$, linear coefficient as $0.005\pm0.008$ and quadratic coefficient as $-0.0014\pm0.0033$. There are two coefficients on the day-night asymmetry: constant coefficient as $0.0496\pm0.0347$ and the linear coefficient as $-0.018\pm0.028$. The day-night asymmetry (0.0496) observed is 1.4$\sigma$ away from zero. Using these findings, the oscillation space in terms of $\Delta m^2_{21}$ and $\theta_{12}$ will be further constrained. Compared to the previous published SNO results, the uncertainty on $^{8}$B went down from 3.83\% to 3.56\% and average $^{8}$B $\nu_e$ survival probability (p$_0$) went down from 6.57\% to 6.14\%. If the data were analysed with the same assumptions, the decrease in uncertainties would have been approximately twice as big; however, more conservative systematic uncertainties were assigned in some cases. \end{Large}
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