Science Programme

The SNO+ Experiment is used to investigate a large suite of physics phenomena.
Find out more about our current active research interests here.

Reactor Neutrinos

Nuclear reactors used for power generation produce enormous numbers of electron anti-neutrinos (typically > 10²⁰ every second) from the beta decays of the fission products. The flux of reactor anti-neutrinos can be accurately calculated from the number of decays, which is related to the measured thermal power produced by each reactor. The precise shape of the anti-neutrino energy spectrum depends on the well known nuclear composition of the fuel used for each reactor. The precise yield and well defined energy spectrum from anti-neutrinos produced a known distance from the detector makes reactor anti-neutrinos very powerful tools to study neutrino oscillations.

Recent measurements of neutrino oscillation parameters from the KamLAND collaboration has produced the most precise measurement to date of Δm²₂₁, one of the parameters used to describe neutrino oscillations. Currently, this measurement is in tension with the value obtained using solar neutrinos on experiments such as SNO and Super-Kamiokande. A measurement of reactor neutrinos using the SNO+ experiment may help to resolve this discrepency.

In scintillator experiments, electron anti-neutrinos (̅νe) are detected through the inverse beta decay reaction with protons (p):

̅ν_e + p → e⁺ + n The positron (e⁺) is produced with a kinetic energy of approximately 1.8 MeV less than the energy of the anti-neutrino E_ν, and annihilates with a nearby electron almost immediately, depositing a total of approximately (E_ν ~ 0.8) MeV in the detector. The tight relationship between the kinetic energies of the detected positron and the anti-neutrino makes analysis of anti-neutrino energy spectra relatively straightforward. The neutron (n) typically captures on a hydrogen atom a few hundred microseconds later, producing a time coincident signal with the positron. This coincidence provides powerful background rejection.

Anti-neutrinos propagate (and therefore oscillate), a fraction of the electron anti-neutrinos produced in the nuclear reactors will change into muon or tau anti-neutrinos, which are not detected. For a fixed distance, the probability that a neutrino oscillates depends on its energy. Thus, the energy spectrum of electron anti-neutrinos observed at the detector differs significantly from the spectrum at production. The expected SNO+ reactor anti-neutrino spectrum (compared with a no oscillation scenario) is shown here, and depends on if the oscillation parameter agrees more with solar experiments (left) or KamLand (right):

SNO+ will primarily measure anti-neutrinos from the Bruce, Pickering, and Darlington nuclear generating stations. Although it is not expected to detect as many events as KamLAND, the peaked structure in the summed oscillation spectrum is much sharper for SNO+ owing to the fortuitous positions of these three Canadian reactors.