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SNO+

SNO+. Mark Chen SNOLAB Workshop August 22, 2007. Outline. science goals focusing on Nd double beta decay R&D activities and progress budget and schedule. SNO+ Origin. SNO+ concept was born in the CFI Proposal for SNOLAB

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SNO+

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  1. SNO+ Mark Chen SNOLAB Workshop August 22, 2007

  2. Outline • science goals • focusing on Nd double beta decay • R&D activities and progress • budget and schedule

  3. SNO+ Origin • SNO+ concept was born in the CFI Proposal for SNOLAB • a deep lab is required to eliminate cosmogenic 11C background to the pep solar neutrino signal in a liquid scintillator detector • part of the Subatomic Physics Five-Year Plan since 2001 • LOI to SNOLAB submitted April 2004

  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 neutrino oscillations • supernova neutrinos • double beta decay

  5. SNO+ Double Beta Decay • …sometimes referred to as SNO++ • it is possible to add bb isotopes to liquid scintillator, for example • dissolve Xe gas • organometallic chemistry (Nd, Se, Te) • dispersion of nanoparticles (Nd2O3, TeO2) • we researched these options and decided that the best isotope and technique is to make a Nd-loaded liquid scintillator

  6. table from F. Avignone Neutrino 2004 150Nd • 3.37 MeV endpoint • (9.7 ± 0.7 ± 1.0) × 1018 yr 2nbb half-life measured by NEMO-III • isotopic abundance 5.6% 1% natural Nd-loaded liquid scintillator in SNO+ has 560 kg of 150Nd compared to 37 g in NEMO-III • cost: $1000 per kg for metallic Nd; cheaper is NdCl3…$86 per kg for 1 tonne

  7. SNO+ Double Beta Decay • a liquid scintillator detector has poor energy resolution; but enormous quantities of isotope (high statistics) and low backgrounds help compensate • large, homogeneous liquid detector leads to well-defined background model • fewer types of material near fiducial volume • meters of self-shielding • possibly source in–source out capability

  8. Nd-Loaded Scintillator • using the carboxylate technique that was developed originally for LENS and now also used for Gd-loaded scintillator • we successfully loaded Nd into pseudocumene and in linear alkylbenzene (>1% concentration) • with 1% Nd loading (natural Nd) we found very good neutrinoless double beta decay sensitivity…

  9. Test <mn> = 0.150 eV Klapdor-Kleingrothaus et al., Phys. Lett. B 586, 198, (2004) 0n: 1000 events per year with 1% natural Nd-loaded liquid scintillator in SNO++ simulation: one year of data maximum likelihood statistical test of the shape to extract 0n and 2n components…~240 units of Dc2 significance after only 1 year!

  10. linear alkylbenzene (LAB) (organic phase) Nd(RCOO)3 (aqueous phase) Nd3+(Cl-)3 + 3RCOO- → Nd(RCOO)3 NH3 + RCOOH → NH4+ + RCOO- Nd-LS Synthesis • solvent-solvent extraction method to synthesize metal-loaded liquid scintillator • this method was used to make Nd-LS at both BNL and Queen’s laboratories

  11. Nd in Various Scintillation Solvents

  12. Light Output from Nd Scintillator • you can see that 1% Nd-loaded scintillator is blue • because Nd absorbs light • fortunately it is blue • it means the blue scintillation light can propagate through • but, not enough light output in SNO+ if using 1% Nd loading • BUT, with enriched Nd (e.g. enrich to 56% 150Nd up from 5.6%) could have the same neutrinoless double beta decay sensitivity using 0.1% Nd loading…

  13. Light Output and Concentration • at 1% loading (natural Nd), there is too much light absorption by Nd • 47±6 pe/MeV (from Monte Carlo) • at 0.1% loading (isotopically enriched to 56%) our Monte Carlo predicts • 400±21 pe/MeV (from Monte Carlo) • good enough to do the experiment

  14. Nd-150 Consortium • SuperNEMO and SNO+, MOON and DCBA are supporting efforts to maintain an existing French AVLIS facility that is capable of making 100’s of kg of enriched Nd • a facility that enriched 204 kg of U (from 0.7% to 2.5%) in several hundred hours

  15. 2000–2003 Program : Menphis facility Evaporator Dye laser chain Yag laser Copper vapor laser Design : 2001 Building : 2002 1st test : early 2003 1st full scale exp. : june 2003

  16. AVLIS for 150Nd is Known

  17. SNO+ Nd Summary So Far… • SNO+ plans to deploy 0.1% Nd-loaded liquid scintillator • ~500 kg of 150Nd if enriched Nd • 56 kg of 150Nd if natural Nd • light output: 400 pe/MeV corresponds to 6.4% resolution FWHM at 150Nd Q-value • why Nd? • high Q-value is above most backgrounds • Ge: Majorana and GERDA • Xe: EXO, XMASS • Te: CUORE • Mo: MOON • Ca: CANDLES • Cd: C0BRA • Nd: SNO+ • how we search for double beta decay? • fit 2n and 0nknown spectral shapes along with knowable background shapes (mainly from internal Th)

  18. SNO+ Double Beta Spectrum 1 yr, 500 kg isotope, mn = 150 meV

  19. Statistical Sensitivity in SNO+ corresponds to 0.1% natural Nd LS in SNO+ 56 kg isotope 500 kg isotope • 3 sigma detection on at least 5 out of 10 fake data sets • 2n/0n decay rates are from Elliott & Vogel, Ann. Rev. Nucl. Part. Sci. 52, 115 (2002)

  20. 0.1% Natural Nd Loading 1yr, 1000kg natural, 150meV

  21. Statistical Sensitivity • for 50% enriched 150Nd (0.1% Nd LS in SNO+) • 3s statistical sensitivity reaches 30 meV • 5s sensitivity of 40 meV after 3 years • for background levels (U, Th) in the Nd LS to be at the same level as KamLAND scintillator • systematic error in energy response will likely be the limit of the experiment and not the statistics • preliminary studies show that we can understand the energy resolution systematics at the level required to preserve sensitivity down to 50 meV

  22. Stability of Nd-LAB no change in optical properties after >1 year

  23. Nd LS Works! small Nd-LS detector with a, b, g sources demonstrates it works as scintillator external 241Am a 207Bi conversion electrons Compton edge 137Cs

  24. Nd Purification • NdCl3 needs to be purified • putting Nd into the organic accomplishes purification (U, Th don’t get loaded into the liquid scintillator) • Nd liquid scintillator: after synthesis it is possible to perform online loop purification • 150Nd enrichment also removes unwanted Th

  25. Radio-purification goals: • 228Th and 228Ra in 10 tonnes of 10% Nd (in form of NdCl3 salt) down to <110-14 g 232Th/g Nd • Raw NdCl3 salt measurement: 228Th equivalents to 32±2510-9g 232Th/g Nd A reduction of >106 is required!!!

  26. Purification Spike Tests • spike scintillator with 228Th (80 Bq) which decays to 212Pb • counted by β- coincidence liquid scintillation counting

  27. Spike Test Results: Extraction Efficiencies of Th and Ra in 10% NdCl3 using HZrO and BaSO4 factor of 1000 purification per pass achieved for both Th and Ra!

  28. SNO+ Nd: Summary • good sensitivity and very timely • homogeneous liquid, well defined background model • large volume gives self-shielding • Q-value is above most backgrounds • thus “insensitive” to internal radon backgrounds • thus insensitive to “external” backgrounds (2.6 MeV g) • Th, Ra purification techniques are effective • huge amounts of isotope, thus high statistics, can work for double beta decay search • requires exquisite calibration and knowledge of detector response

  29. p-p Solar Fusion Chain p + p  2H + e+ + e p + e− + p  2H + e 2H + p  3He +  CNO Cycle 3He + 3He  4He + 2 p 3He + p  4He + e+ + e 12C + p →13N + g 13N → 13C + e+ + ne 13C + p → 14N + g 14N + p → 15O + g 15O → 15N + e+ + ne 15N + p → 12C + a 3He + 4He  7Be +  7Be + e−  7Li +  + e 7Be + p  8B +  7Li + p   +  8B  2  + e+ + e Low Energy Solar Neutrinos • complete our understanding of neutrinos from the Sun pep, CNO, 7Be, pp

  30. Ga, Cl and SNO Data – Distilled deduce the survival probability high energy: directly from SNO medium energy: Cl minus high low energy: Ga minus high, medium qx is q13 we observe that the survival probability for solar neutrinos versus energy is not yet accurately determined from existing experiments Barger, Marfatia, Whisnant, hep-ph/0501247 transition between vacuum and matter oscillations in the Sun has not been accurately determined there is even some tension in existing low and medium data…

  31. Things You Could Learn …with precision data from low energy solar neutrinos • fix Dm2 with KamLAND data, vary q13 (with q12 fixed or varying) • low energy solar neutrino data helps constrain q13 • extract Dm2 from solar data, strongly affected by the position of the transition – low energy solar neutrino data are key – compare with Dm2 from KamLAND • neutrinos versus antineutrinos, tests CPT invariance • compare position/shape of the transition at lower energy with the prediction from LMA MSW oscillations • might reveal deviations from Standard Model couplings (due to non-standard interactions or coupling to a sterile neutrino admixture) …and many of these studies have been done, all pointing to the fact that at the transition (between 1-2 MeV) there is sensitivity to new neutrino physics! (e.g. Balantekin or Friedland, Peña-Garay, Lunardini, or Barger and colleagues…)

  32. Neutrino-Matter Interaction • best-fit oscillation parameters suggest MSW occurs • but we have no direct evidence of MSW • day-night effect not observed • no spectral distortion for 8B n’s • testing the vacuum-matter transition is sensitive to new physics from Peña-Garay for Dm2 = 8 × 10−5 eV2, q = 34° Ne at the centre of the Sun → E is 1-2 MeV Hamiltonian for neutrino propagation in the Sun

  33. New Physics good fit with NSI • MSW is linear in GF and limits from n-scattering experiments ( g2) aren’t that restrictive • oscillation solutions with NSI can fit existing solar and atmospheric neutrino data…NSI not currently constrained • new pep solar n data would reveal NSI pep solar neutrinos are at the “sweet spot” to test for new physics Friedland, Lunardini, Peña-Garay, hep-ph/0402266

  34. Mass-Varying Neutrinos • cosmological connection: mass scale of neutrinos and the mass scale of dark energy are similar • postulating a scalar field and neutrino coupling results in neutrinos whose mass varies with the background field (e.g. of other neutrinos) • solar neutrinos affected? • pep n: a sensitive probe Fardon, Nelson, Weiner, hep-ph/0309800 pep Barger, Huber, Marfatia, hep-ph/0502196

  35. Why pep Solar Neutrinos? stat + syst + SSM errors estimated SSM pep flux: uncertainty ±1.5% known source known cross section (n-e scattering) → measuring the rate gives the survival probability →precision test Dm2 = 8.0 × 10−5 eV2 tan2q = 0.45 for neutrino physics with low energy solar neutrinos, have to achieve precision similar to SNO or better…it’s no longer sufficient to just detect the neutrinos SNO CC/NC pep solar neutrinos: En = 1.44 MeV …are at the right energy to search for new physics observing the rise confirms MSW and our understanding of solar neutrinos pepn

  36. 11C Cosmogenic Background these plots from the KamLAND proposal muon rate in KamLAND: 26,000 d−1 compared with SNO: 70 d−1

  37. Requirements for a Liquid Scintillator pep Solar n Detector • depth • to reduce/eliminate 11C background • good light output from the scintillator • studied the effect of varying the energy resolution; found not a steep dependence • radiopurity • control of Rn exposure because of 210Bi • eliminate 40K internal contamination

  38. Solar Signals with Backgrounds

  39. SNO+ Solar Neutrino Projected Capability • with backgrounds at KamLAND levels • U, Th achieved • 210Pb and 40K post-purification KamLAND targets • external g backgrounds • calculated based upon SNO external activities • fiducial volume 450 cm • pep uncertainties • <±5% statistical (signal extraction from background) • ±3% systematic • ±1.5% SSM • e.g. it would be a measurement of the survival probability at 1.44 MeV of 0.55 ± 0.03

  40. pep Sensitivity Dependence on 210Pb allowing 210Pb contamination to increase by large factors does not have a large impact on the pep statistical uncertainty

  41. pepn and q13 • solar neutrinos are complementary to long baseline and reactor experiments for q13 • hypothetical 5% stat. 3% syst. 1.5% SSM measurement • has discriminating power for q13 pep

  42. Geo-Neutrino Signal • antineutrino events ne + p → e+ + n: • KamLAND: 33 events per year (1000 tons CH2) / 142 events reactor • SNO+: 44 events per year (1000 tons CH2) / 38 events reactor KamLAND SNO+ geo-neutrinos and reactor background KamLAND geo-neutrino detection…July 28, 2005 in Nature

  43. Reactor Neutrino Oscillations 50 km Bruce 240 km oscillation spectral features depend on Dm2 and move as L/E Pickering 340 km Darlington 360 km

  44. SN Neutrino Detection in SNO+ SNO+ vs. Super-Kamiokande CC: (260) 41% (7000) 91% (30) 4.7% (10) 1.5% NC: (60) 9.3% (410) 5% (270) 42% ES: (12) 1.9% (300) 4% Clarence J. Virtue NSERC SNO+ Review - 27 November 2006

  45. Steps Required: SNO → SNO+ • AV hold down • liquid scintillator procurement • scintillator purification • “minor” upgrades • cover gas • electronics • DAQ • calibration

  46. SNO+ Liquid Scintillator • “new” liquid scintillator developed • linear alkylbenzene (LAB) • compatible with acrylic, undiluted • high light yield • pure (light attenuation length in excess of 20 m at 420 nm) • low cost • high flash point 130°C safe • low toxicity safe • smallest scattering of all scintillating solvents investigated • density r = 0.86 g/cm3 • metal-loading compatible • SNO+ light output (photoelectrons/MeV) will be approximately 3-4× that of KamLAND • ~900 p.e./MeV for 54% PMT area coverage • Daya Bay and Hanohano plan to use LAB; others LENS, Double CHOOZ,LENA, NOnA considering

  47. SNO+ AV Hold Down Existing AV Support Ropes

  48. SNO+ AV Hold Down Existing AV Support Ropes AV Hold Down Ropes

  49. SNO+ R&D 2005Proof of Principle • linear alkylbenzene developed by SNO+ as the liquid scintillator • AV hold-down for specific gravity 0.86 is feasible (study by Bob Brewer) • double beta decay potential investigated • made 1.0% Nd-loaded scintillator

  50. SNO+ 2006Expanded R&D • AV hold-down implementation plan developed • designs for cover gas and universal interface being prepared • radon daughter removal from acrylic studied • scintillator purification tests: factor >1000 achieved • initial conceptual design and layout for scintillator purification and handling • simulations: signals and backgrounds • continued scintillator-acrylic compatibility tests • learned of the existence of French AVLIS facility for enriching neodymium all major questions have been answered

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