Neutron Measurements and Reactor Antineutrino Search with the SNO+ Detector in the Water Phase
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Authors
Liu, Yan
Date
Type
thesis
Language
eng
Keyword
SNO+ , Neutrino Physics , Reactor Antineutrinos , Neutron Capture
Alternative Title
Abstract
The SNO+ experiment is a large-scale liquid scintillator neutrino experiment with a wide range of physics objectives. SNO+ has adopted a staged approach where the detector was first filled with ultra-pure water before substituting with liquid scintillator and the target isotope $^{130}$Te for neutrinoless double beta decay. During the SNO+ water phase, an $^{241}$Am$^{9}$Be source is deployed across the detector volume to calibrate the detector's energy response and its response to neutrons. The $^{241}$Am$^{9}$Be source emits a unique coincidence signal with the prompt event being a 4.4 MeV $\gamma$ and the delayed a neutron capture signal (2.2 MeV $\gamma$).
A novel, minimalistic, statistical analysis of the $^{241}$Am$^{9}$Be calibration data was designed and used to measure the capture time constant $\tau$, capture cross-section $\sigma_{H,t}$, and the neutron detection efficiency $E_{\textrm{center}}$ at the center of the detector:
\begin{equation}
\begin{aligned}
&\tau = 202.35 \pm 0.42\ (stat.)\ ^{+0.38}_{-0.31}\ (syst.)~\mu\textrm{s}, \\
&\sigma_{H,t} = 336.3 ^{+1.2}_{-1.5}~\textrm{mb}, \\
&E_{\textrm{center}} = (50.8 \pm 0.6)\%.
\end{aligned}
\end{equation}
Additionally, with the help of Monte Carlo simulations, a volume-weighted neutron detection efficiency across the detector is evaluated to be $E_{\textrm{detector}} = (46.5 \pm 0.5\ (stat.\ only))\%$. The simulation is also central to an energy calibration using the 4.4 MeV $\gamma$ to measure the energy resolution and energy scale of the detector.
Finally, with $\sim$115 days of early water data, an upper limit, $\hat{\Phi}_{\bar{\nu}_e, \textrm{ult}}$ = $(1.76 \pm 0.29) \times 10^6 \bar{\nu}/(\textrm{cm}^2\cdot\textrm{s})$, on the reactor antineutrino flux for SNO+ is obtained using a maximum likelihood approach. The limit is about a factor of 9 higher than the expected signal in SNO+, which can be calculated using available reactor output power data.
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ProQuest PhD and Master's Theses International Dissemination Agreement
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Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.