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SNO+: A Geoneutrino Detector for the Continental Crust

SNO+: A Geoneutrino Detector for the Continental Crust. AGU 2006 Joint Assembly Baltimore, MD. Mark Chen Queen’s University. Sudbury Neutrino Observatory. 1000 tonnes D 2 O 12 m diameter Acrylic Vessel 18 m diameter support structure; 9500 PMTs (~60% photocathode coverage)

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SNO+: A Geoneutrino Detector for the Continental Crust

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  1. SNO+: A Geoneutrino Detector for the Continental Crust AGU 2006 Joint Assembly Baltimore, MD Mark Chen Queen’s University

  2. Sudbury Neutrino Observatory 1000 tonnes D2O 12 m diameter Acrylic Vessel 18 m diameter support structure; 9500 PMTs (~60% photocathode coverage) 1700 tonnes inner shielding H2O 5300 tonnes outer shielding H2O Urylon liner radon seal depth: 2092 m (~6010 m.w.e.) ~70 muons/day

  3. End of SNO • Fall 04 to Dec 06: SNO Phase III • 3He proportional counter array • dedicated Neutral Current Detectors (NCDs) • taking production data • data taking end date: 31 Dec 2006 • will bring total uncertainty on 8B solar n NC signal below 5% • physics with heavy water will be complete • heavy water will be returned to AECL in 2007 what should be done next?

  4. Fill with Liquid Scintillator • SNO plus liquid scintillator → physics program • pep and CNO low energy solar neutrinos • tests the neutrino-matter interaction, sensitive to new physics • geo-neutrinos • 240 km baseline reactor oscillation confirmation • supernova neutrinos • double beta decay?

  5. SNO+ Technical Issues • liquid scintillator selection • compatibility with acrylic vessel • high light yield, long attenuation length • reversing the acrylic vessel mechanics • SNO: AV contains heavy water, must hold up • SNO+: AV contains scintillator, r < 1 g/cm3, must hold down • liquid scintillator purification

  6. Acrylic Vessel Hold-down • “rope net” being designed to hold down 15% density difference (buoyancy) SNO SNO+

  7. SNO+ Technical Progress • liquid scintillator identified • linear alkylbenzene • compatible with acrylic, undiluted • high light yield • pure (light attenuation length in excess of 20 m at 420 nm) • low cost • high flash point • low toxicity • smallest scattering of all scintillating solvents investigated • density r = 0.86 g/cm3 • SNO+ light output (photoelectrons/MeV) will be approximately 4× that of KamLAND

  8. Detecting Geo-Neutrinos • reaction:ne + p e++ n • delayed coincidence signal • neutron capture: 2.2 MeV g, t = 0.2 ms • reaction threshold: 1.8 MeV • natural isotopes with Qb > 1.8 MeV • 214Bi, 234Pa (U chain) • 228Ac, 212Bi (Th chain)

  9. Geo-Neutrino Signal • event rates: • KamLAND: 33 events per year (1000 tons CH2) / 142 events reactor • SNO+: 44 events per year (1000 tons CH2) / 42 events reactor KamLAND SNO+ geo-neutrinos and reactor background KamLAND geo-neutrino detection…July 28, 2005 in Nature

  10. Location, Location, Location Bruce Pickering Darlington

  11. Other Backgrounds • 13C(a,n): hope to control this background by controlling Rn exposure in the scintillator • accidental backgrounds: should be small, like in KamLAND • cosmogenic isotope production (e.g. 9Li): tiny background in KamLAND, even lower in SNO+ • solar ne break up of 2H: could be higher in SNO+, if residue of deuterons from heavy water!

  12. DepthMatters!

  13. U and Th Separation • from Enomoto, Ohtani, Inoue, Suzuki, hep-ph/0508049 (2005) • in KamLAND “separation of U and Th neutrinos seems to be still difficult due to large backgrounds from surrounding nuclear power reactors” • “absence of reactor neutrino backgrounds enables … to observe U and Th geo-neutrinos separately” • may be possible in SNO+ dotted lines w/o reactor solid lines w/ reactor

  14. Geo-n from Continental Crust crust: blue mantle: black total: red in SNO+

  15. Have Cake, Eat it too… • SNO+ geo-n signal dominated by continental crust; checks basic geochemical ideas about the crust • the local geology around SNO+ • Canadian Shield (more general, the North American Craton) • old, thick, well-understood continental crust • mining activities near Sudbury suggest that the very local geology is extremely well studied • if the local U, Th content in the surrounding rocks is already well constrained, it is possible that the deep Earth (e.g. mantle) component in the SNO+ geo-n signal can be inferred • i.e. the local crust component is subtracted off from the signal, leaving the mantle component

  16. Toy Calc – Mantle Component • 70-30: the 70 component has 10% uncertainty; that’s ±7 on the 30 component which is = 0.23 • 80-20: the 80 component has 5% uncertainty; that’s ±4 on the 20 component which is = 0.20

  17. Conclusions • SNO+ geo-neutrinos: a good follow-up to KamLAND’s first detection • potential to really constrain the radiogenic heat flow • potential for geochemistry (separate measurement of U and Th) • by doing the above, one is testing models of Earth’s chemical origin • surrounding geology is simpler, leading to potentially smaller uncertainties in inferred, deep-Earth component

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