Thesis

Low energy anti-neutrino detection in SNO+

• Call:

  IDPASC Portugal - PHD Programme 2016

• Academic Year:

  2016 / 2017

• Domains:

  Experimental Particle Physics | Astroparticle Physics

• Supervisor:

  Sofia Andringa

• Co-Supervisor:

  Amelia Maio

• Institution:

  Faculdade de Ciências - Universidade de Lisboa

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  The first observations of geo-neutrinos, i.e. anti-neutrinos produced by natural radioactivity in the planet's crust and mantle, are recent but are already being used to test Earth models; anti-neutrinos produced in nuclear reactors have been classically used in neutrino physics, namely for the study of neutrino oscillations. Anti-neutrinos are also used to detect near-by Supernovae and an increase in low energy anti-neutrinos is expected even some days before the explosion. 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 is to search for neutrinoless double beta decay of Tellurium, but anti-neutrino detection is also possible. The expected rates of anti-neutrinos are small, but they can be clearly identified by the delayed coincidence of a positron annihilation followed by a neutron capture. The positron energy and the neutron initial direction follow the anti-neutrino kinematics, and we aim to use both to help in the separation of the fluxes of reactor and geo-neutrinos, and also in the separation between them and similar background signals. In fact, alpha particles created by natural radioactivity inside the detector can create neutrons giving rise to a similar coincidence signature, dominant at low energy. The amount of background will only be known at the start of the experiment and its distribution will evolve with time, needing a constant monitoring (which may also be used for early Supernova detection monitoring). The SNO+ experiment will have a commissioning data taking period this year, first with a water target. It will later be replaced with scintillator needed for the anti-neutrino measurements. The LIP group is responsible for several aspects of the calibration system – PMT and scintillator optical calibration, source insertion mechanism – as well as for the anti-neutrino analysis. The proposed work plan will involve all aspects of the anti-neutrino data analysis, focusing on the low energy part where all signals overlap and on the corresponding background monitoring. This includes the development of selection algorithms for neutron identification and coincidence techniques, particle identification methods to separate alpha from positron signals, and modeling of the signals and background spectra and evolution. The work will include also participation in in-situ activities in SNOLAB, including in the early stages the commissioning of the calibration systems, and later on, data-taking and calibration data analysis.