Neutron Measurements and Reactor Antineutrino Search with the SNO+ Detector in the Water Phase

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 ¹³⁰Te for neutrinoless double beta decay. During the SNO+ water phase, an ²⁴¹Am⁹Be source is deployed across the detector volume to calibrate the detector's energy response and its response to neutrons. The ²⁴¹Am⁹Be source emits a unique coincidence signal with the prompt event being a 4.4 MeV γ and the delayed a neutron capture signal (2.2 MeV γ). A novel, minimalistic, statistical analysis of the ²⁴¹Am⁹Be calibration data was designed and used to measure the capture time constant $\tau$, capture cross-section σ_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 γ 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 10⁶ \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.

Department dc:contributor.department

Physics, Engineering Physics and Astronomy

Author dc:creator

• Liu, Yan

Advisor dc:contributor.supervisor

• Chen, Mark

• SNO+
• Neutrino Physics
• Reactor Antineutrinos
• Neutron Capture

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1974/27931

OAI identifier oai:identifier

oai:queensu.scholaris.ca:1974/27931