Thesis

A study of the neutrino double beta decay in SNO+ and its implication on the NLDBD channel

• Call:

  IDPASC Portugal - PHD Programme 2016

• Academic Year:

  2016 / 2017

• Domain:

  Experimental Particle Physics

• Supervisor:

  Fernando Barao

• Co-Supervisor:

  Gersende Prior

• Institution:

  Instituto Superior Técnico

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  The Sudbury Neutrino Observatory (SNO) is a large volume neutrino detector located in the SNOLAB underground laboratory in Canada. SNO has demonstrated that solar neutrinos do change flavour and thus have a small, but non-zero, mass. The SNO+ experiment replaces the SNO's heavy water target by liquid scintillator, which will provide sensitivity to several new low energy measurements. The main goal of SNO+ is to search for neutrinoless double beta decay (NLDBD) of Tellurium, but anti-neutrino detection is also possible during all the phases of the experiment. Double beta decay (DBD), in which the nucleus emits two electrons alongside two (anti-)neutrinos, is a rare nuclear decay that has been observed in several isotopes, among which Te-130. The process of neutrino-less double beta decay (NLDBD), in which only two electrons are emitted by the nucleus, is possible only if the neutrinos can annihilate with each other and so is considered to be the most viable way to show whether neutrinos are Dirac or Majorana fermions. Searching for neutrino-less or neutrino double beta decay is an extremely sensitive process. As experiments are looking for a peak in the energy spectrum within a set of several backgrounds, they have to concentrate on background characterization and/or suppression. In particular, the search for events from neutrino-less double beta decay has to deal with the irreducible double-beta decay channel electron spectra, whose energy tail overlaps the neutrino-less electron peak. In the SNO+ experiment, around 25% of DBD events are expected in the fiducial analysis region. Therefore and taking into account the large quantity of Te-130 isotope, existing in SNO+, it is important to evaluate the half-life of the Te-130 isotope and constrain the "background" resulting from the DBD channel. Such a calculation will imply also an evaluation of the exposure time of the experiment together with he analysis efficiency. The aim of this thesis proposal is to address the measurement of Te-130 half-time and its implication on the neutrino-less double beta decay analysis with Te-130 in the SNO+ experiment.