46°28′30″N81°12′04″W / 46.475°N 81.201°W /46.475; -81.201
SNO+ is aphysics experiment designed to search forneutrinoless double beta decay, with secondary measurements ofproton–electron–proton (pep) solarneutrinos,geoneutrinos from radioactive decays in the Earth, and reactor neutrinos. It could also observesupernovae neutrinos if a supernova occurs in our galaxy. It is under construction (as of February 2017) using the underground equipment already installed for the formerSudbury Neutrino Observatory (SNO) experiment atSNOLAB.
The primary goal of the SNO+ detector is the search forneutrinoless double beta decay, specifically with regard to decay of130
Te
,[1] to understand if a neutrino is its own anti-particle (i.e. amajorana fermion). Secondary physics goals include measurement of neutrinos or antineutrinos from:
The previous experiment, SNO, used heavy water (D2O) within the sphere and relied onCherenkov radiation interaction. The SNO+ experiment will use the sphere filled withlinear alkyl benzene to act as a liquidscintillator and target material.[2] The sphere is surrounded withphotomultiplier tubes and the assembly is floated in water and the sphere held down against the resulting buoyant forces by ropes. Testing (filled with water) is expected to begin early 2016, with full operation with liquid a few months after that, and Tellurium loading begins in 2017.[1]
Aneutrino interaction with this liquid produces several times more light than an interaction in a waterCherenkov experiment such as the original SNO experiment orSuper-Kamiokande. The energy threshold for the detection of neutrinos can, therefore, be lower, andproton–electron–protonsolar neutrinos (with an energy of1.44 MeV) can be observed. In addition, a liquid scintillator experiment can detect anti-neutrinos like those created in nuclear fission reactors and the decay ofthorium anduranium in the earth.
SNO+ uses 780 tonnes oflinear alkylbenzene as the scintillator (the detector started to be filled with the scintillator at the end of 2018[3]) and will be filled with130
Te
[1] in the future. Originally the plan was to fill with 0.3%130
Te
(800 kg),[1] but later talks have cited 0.5% (1.3 tonnes)[4]
Earlier proposals placed more emphasis on neutrino observations. The current emphasis on neutrinoless double beta decay is because the interior of theacrylic vessel has been significantly contaminated by radioactivedaughter products of theradon gas that is common in the mine air. These couldleach into the scintillator, where some would be removed by the filtration system, but the remainder may interfere with low-energy neutrino measurements.[5] The neutrinoless double beta decay observations are not affected by this.[5]
The project received funding for initial construction fromNSERC in April 2007. As of early 2013, the cavity had been refurbished and re-sealed to new cleanliness standards, more stringent than for the original SNO due to the new experiment's greater sensitivity.
The main civil engineering challenge is that the current SNO vessel is supported by a series of ropes, to prevent the weight of the heavy water inside from sinking it in the surrounding normal water. The proposed liquid scintillator (linear alkylbenzene) is lighter than water, and must be held down instead, but still without blocking the view of its interior. The existing support rope attachment points, cast into the acrylic sphere's equator, are not suitable for upside-down use.
The collaboration is investigating the use ofgrid resources to deliver the computing power needed by the experiment. This is after the success of theLHC Computing Grid (wLCG) used by theLHC experiments. The SNO+VO has been using resources provided byGridPP.[6]