The SNO+ liquid scintillator response to low-energy electrons and its effect on the experiment’s sensitivity to a future neutrinoless double beta decay signal

• Author / Creator

  Sibley, Logan AB

• The SNO+ experiment is set to join the international competition of experiments searching for neutrinoless double beta decay. By loading 780 t of liquid scintillator with 0.5% natural tellurium, and with its location 2 km underground at SNOLAB, SNO+ aims to have sensitivity to determining the Majorana nature of the neutrino, a question currently at the forefront of particle physics, approaching the inverted hierarchy of the neutrino masses. To reach this sensitivity, it is crucial that SNO+ understands the response of the liquid scintillator, as systematic uncertainties on the energy scale and resolution, in particular any non-Gaussian shape of the energy resolution, may diminish the experiment’s sensitivity in a significant way. A 60Co calibration source that tags calibration events within the liquid scintillator will enable SNO+ to precisely study the shape of the energy resolution near the endpoint of the 130Te double beta decay. Monte Carlo simulations of the calibration source predict it will measure a 3.24% energy resolution at an energy of 2.51 MeV. Because 60Co emits two gamma-rays upon decaying, whereas the expected signal of neutrinoless double beta decay is the sum of two electrons, it is also crucial for SNO+ to understand how the response of the liquid scintillator depends on particle type and energy. This dissertation provides the first measurement of the SNO+ tellurium-loaded liquid scintillator response to low-energy electrons. Ionization quenching of low-energy electrons in the tellurium-loaded liquid scintillator is small, with Birks’ constant measured to be kB = (4.1 ± 2.9) × 10−6 cm/keV.

• Subjects / Keywords

  • Neutrino
  • Ionization quenching
  • Calibration
  • Double beta decay
  • Neutrinoless double beta decay
  • Liquid scintillator

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3WM1445C

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.