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SNO+ is a
physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
experiment designed to search for
neutrinoless double beta decay The neutrinoless double beta decay (0νββ) is a commonly proposed and experimentally pursued theoretical radioactive decay process that would prove a Majorana nature of the neutrino particle. To this day, it has not been found. The discovery o ...
, with secondary measurements of proton–electron–proton (''pep'') solar
neutrino A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...
s,
geoneutrino A geoneutrino is a neutrino or antineutrino emitted in decay of radionuclide naturally occurring in the Earth. Neutrinos, the lightest of the known subatomic particles, lack measurable electromagnetic properties and interact only via the weak nucl ...
s from radioactive decays in the Earth, and reactor neutrinos. It is under construction (as of February 2017) using the underground equipment already installed for the former
Sudbury Neutrino Observatory The Sudbury Neutrino Observatory (SNO) was a neutrino observatory located 2100 m underground in Vale's Creighton Mine in Sudbury, Ontario, Canada. The detector was designed to detect solar neutrinos through their interactions with a large ...
(SNO) experiment at
SNOLAB SNOLAB is a Canadian underground science laboratory specializing in neutrino and dark matter physics. Located 2 km below the surface in Vale's Creighton nickel mine near Sudbury, Ontario, SNOLAB is an expansion of the existing facilities con ...
. It could also observe supernovae neutrinos if a supernova occurs in our galaxy.


Physics goals

The primary goal of the SNO+ detector is the search for
neutrinoless double beta decay The neutrinoless double beta decay (0νββ) is a commonly proposed and experimentally pursued theoretical radioactive decay process that would prove a Majorana nature of the neutrino particle. To this day, it has not been found. The discovery o ...
, specifically with regard to decay of , to understand if a neutrino is its own anti-particle (i.e. a majorana fermion). Secondary physics goals include measurement of neutrinos or antineutrinos from: * Proton-electron-proton (pep) and carbon-nitrogen-oxygen (CNO) cycles within the Sun to better understand neutrino-matter interaction and solar composition. * Beta decay of
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
and
thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
within the Earth (
geoneutrino A geoneutrino is a neutrino or antineutrino emitted in decay of radionuclide naturally occurring in the Earth. Neutrinos, the lightest of the known subatomic particles, lack measurable electromagnetic properties and interact only via the weak nucl ...
s) to constrain Earth's radioactive heat budget. * Beta decay of fission daughter products in nuclear reactors (reactor antineutrinos) to better constrain neutrino oscillation parameters. * Supernova neutrinos and antineutrinos for early warning detection of supernova (see Supernova Early Warning System). * Nucleon decay into neutrinos, which would indicate a violation of baryon conservation.


Testing and construction

The previous experiment, SNO, used water within the sphere and relied on Cherenkov radiation interaction. The SNO+ experiment will use the sphere filled with linear alkyl benzene to act as a liquid scintillator and target material. The sphere is surrounded with
photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal. Kinds of photomultiplier include: * Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sh ...
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. A
neutrino A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...
interaction with this liquid produces several times more light than an interaction in a water Cherenkov experiment such as the original SNO experiment or
Super-Kamiokande Super-Kamiokande (abbreviation of Super-Kamioka Neutrino Detection Experiment, also abbreviated to Super-K or SK; ja, スーパーカミオカンデ) is a Neutrino detector, neutrino observatory located Kamioka Observatory, under Mount Ikeno ...
. The energy threshold for the detection of neutrinos can, therefore, be lower, and proton–electron–proton solar neutrinos (with an energy of ) can be observed. In addition, a liquid scintillator experiment can detect anti-neutrinos like those created in nuclear fission reactors and the decay of
thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
and
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
in the earth. SNO+ uses 780 tonnes of linear alkylbenzene as the scintillator (the detector started to be filled with the scintillator at the end of 2018 ) and will be filled with in the future. Originally the plan was to fill with 0.3% (800 kg), but later talks have cited 0.5% (1.3 tonnes) Earlier proposals placed more emphasis on neutrino observations. The current emphasis on neutrinoless double beta decay is because the interior of the
acrylic Acrylic may refer to: Chemicals and materials * Acrylic acid, the simplest acrylic compound * Acrylate polymer, a group of polymers (plastics) noted for transparency and elasticity * Acrylic resin, a group of related thermoplastic or thermosett ...
vessel has been significantly contaminated by radioactive daughter products of the
radon Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...
gas that is common in the mine air. These could
leach Leach may refer to: * Leach (surname) * Leach, Oklahoma, an unincorporated community, United States * Leach, Tennessee, an unincorporated community, United States * Leach Highway, Western Australia * Leach orchid * Leach phenotype, a mutation in ...
into the scintillator, where some would be removed by the filtration system, but the remainder may interfere with low-energy neutrino measurements. The neutrinoless double beta decay observations are not affected by this. The project received funding for initial construction from
NSERC The Natural Sciences and Engineering Research Council of Canada (NSERC; french: Conseil de recherches en sciences naturelles et en génie du Canada, CRSNG) is the major federal agency responsible for funding natural sciences and engineering rese ...
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.


Computing

The collaboration is investigating the use of
grid Grid, The Grid, or GRID may refer to: Common usage * Cattle grid or stock grid, a type of obstacle is used to prevent livestock from crossing the road * Grid reference, used to define a location on a map Arts, entertainment, and media * News ...
resources to deliver the computing power needed by the experiment. This is after the success of the LHC Computing Grid (wLCG) used by the LHC experiments. The SNO+ VO has been using resources provided by
GridPP GridPP is a collaboration of particle physicists and computer scientists from the United Kingdom and CERN. They manage and maintain a distributed grid computing, computing grid across the UK with the primary aim of providing resources to particle ...
.


References


Further reading


SNO+ Letter of Intent

The SNO+ detector

Past, present and future of SNO: SNO, SNO+ and SNOLAB
(pdf)
Current Status and Future Prospects of the SNO+ Experiment
(Nov 2015)


External links


SNO+ home page

SNO+ experiment
record on INSPIRE-HEP {{Neutrino detectors Neutrino observatories Particle experiments