SNO+

SNO+ is an underground physics experiment under construction (as of February 2008) that makes use of the equipment already installed underground for the (no longer operating) Sudbury Neutrino Observatory (SNO) experiment at SNOLAB. The main physics goals are the measurement of pep (see proton-proton chain reaction) solar neutrinos, geo-neutrinos (neutrinos from radioactive decays in the earth's core, mantle, and crust) and neutrinoless double beta decay.

In order to reach these goals liquid scintillator will be used as target material. A neutrino interaction with this liquid produces several times more light than an interaction in a water Čerenkov experiment such as Super Kamiokande or SK. The energy threshold for the detection of neutrinos therefore can be lower and proton-electron-proton (pep) neutrinos 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 and uranium in the earth. The option of a measurement of neutrinoless double beta decay in SNO+ (also called SNO++) can be achieved by adding ¹⁵⁰Nd to the scintillator. A mass of several hundred kg of double beta decaying material could be added to the experiment. This would make SNO++ the largest experiment to study neutrinoless double beta decays.

The project received funding for initial construction from NSERC in April 2007, and as of February 2008, the SNO heavy water has been drained and the equipment that was inaccessible for 9 years is being refurbished.

The main 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.

References

* [http://snoplus.phy.queensu.ca/ SNO+ home page]
* [http://www.sno.phy.queensu.ca/~alex/SNOLab.pdf SNO+ Letter of Intent]
* [http://neutrino.lbl.gov/~snoman/NuPreTown/slides/Chen_SNOplus.pdf The SNO+ detector]
* [http://indico.lal.in2p3.fr/getFile.py/access?contribId=s11t1&resId=0&materialId=0&confId=a05162 Past, present and future of SNO: SNO, SNO+ and SNOLAB] (pdf)