SNO+ Calibration in Scintillator Phase

The SNO+ experiment is a multi-purpose neutrino detector located 2 km underground at SNOLAB in Vale’s Creighton Mine in Sudbury, Ontario. The centerpiece of SNO+ is a 12-m diameter acrylic vessel (AV), containing the target medium. The AV is surrounded by 7 kilotonnes of external ultrapure water shielding and about 9400 photomultiplier tubes. SNO+ is operating in three phases, defined by the target medium: water, scintillator, and scintillator loaded with tellurium. The physics program at SNO+ includes solar neutrino measurements, antineutrino detection, supernova neutrino monitoring, and the main physics goal: neutrinoless double beta decay search. All of these physics analyses require precise measurements of the detector’s optical and timing responses using known sources to establish constraints on the energy and position reconstruction within the detector. In its water phase, SNO+ calibrated using optical and radioactive sources developed for its predecessor, the SNO experiment, and these calibrations provide external background measurements and baseline calibration constants for the detector. The radioactive sources include the 16N and AmBe sources. The tagged 6.13 MeV γs of the 16N source provided a clean calibration sample in the energy region of interest for both the 8B solar neutrinos measurement and the invisible nucleon decay search during the water phase. Currently in the scintillator phase, some of these sources have been leveraged to provide calibration information of the scintillator from outside of the AV. These calibrations allow for measurement of the internal background and validation of the external background measured in the water phase. These calibration results will be presented. New calibration deployment systems and sources are in development to allow for calibration in the scintillator inside the AV. The status of these developments will be described. The findings from both internal and external calibrations will inform the SNO+ physics analyses.