Scintillator phase of the SNO+ experiment

Mathematik und Naturwissenschaften Institut für Kern- und Teilchen Physik Scintillator phase of the experiment Valentina Lozza On behalf of Collaboration TAUP2011, 05.09.2011 Munich

Outline = SNO + Liquid Scintillator - New detector design - Liquid scintillator Phases of Operation: - Scintillator phase - Nd loaded phase Solar neutrinos - pep - CNO Geo and reactor neutrinos Summary

Detector 780t of liquid scintillator (LAB) Active medium PSUP = PMT Support Structure ~9500 PMT ~ 54% coverage Acrylic Vessel Φ=12 m, thickness = 5 cm Light water (H2O) shielding - 1700t internal - 5300t external Urylon Liner and Radon Seal

New ropes hold down system Liquid scintillator is lighter than water (ρ=0.86 g/cm3) From SNO To Hold up Hold down

Liquid scintillator LAB Linear alkylbenzene (LAB) identified as the liquid scintillator solvent Chemical compatibility with acrylic High light yield (50-100 times higher than D2O) Good optical transparency Low scattering Fast decay, different for alphas and betas High purity available Safe Low toxicity High flash point 130 C Boiling point 278-314 C Environmentally safe Low solubility in water 0.041 mg/l Inexpensive Petresa Plant Bécancour, QC

Phases of operation Two main phases of operation: Liquid Scintillator Phase Solar Neutrinos Reactor and Geo-Neutrinos Supernovae Neutrinos Nd-Loaded phase Neutrinoless Double-Beta decay Reactor and Geo-Neutrinos Supernovae Neutrinos Other interesting studies: nucleon decay, sterile neutrinos,...

Nd loaded phase Neutrinoless double beta decay with liquid scintillator: Large mass, low background Poor energy resolution (3.5% at Nd endpoint) Use 150Nd : High Q-value (3371 kev) low background Successfully loaded in LAB. 0.1% loading Optimized 0.3% under study See Jeffrey Hartnell talk Double Beta Decay, Neutrino Mass W4

Scintillator phase: Solar neutrinos Complete our understanding of the solar neutrino fluxes (complementary to SNO) Next target measurement: pep, 7Be and 8B neutrinos Possibility to further extend into pp region (depending on 14C and 85Kr levels) Probe solar metallicity with CNO (spectrum shape very close to the 210Bi one)

pep neutrinos, Why? pep solar neutrino component is favorable due to: - single energy (1.442 MeV) - very well predicted flux (1.1 % uncertainty) Accurate measurements of neutrino survival probabilities in the low energy range can: - improve the precision on the oscillation parameters - provide sensitivity to alternative models of neutrino mixing Friedland, Lunardini, Peña-Garay, PLB 594 (2004) Good probe for NSI pep solar neutrino as a test for MSW present data suggest MSW testing the vacuum-matter transition is sensitive to new physics Vacuum dominated oscillation solutions with NSI can fit existing solar and atmospheric neutrino data NSI not currently constrained new pep solar neutrino data would test NSI Matter dominated

pep neutrinos, Requirements Requirements for measuring the pep neutrino flux 1. Depth reduce the background induced by cosmogenic muons (11C) 2. Good light output from the scintillator 3. Radiopurity - 14C is not a problem since pep signal is at higher energy - U, Th not a problem if one can repeat KamLAND scintillator purity - 40K, 210Bi (Radon daughter) - 85Kr, 210Po not a problem since pep signal is at higher energy

pep neutrinos, 11C 11C decays are the major background in pep energy window Since they are produced by cosmic muons, the deeper the experiment the better the background KamLAND Borexino Eμ [GeV] 350 260 270 n12c[x1031] 4.54 4.30 (all C) 4.51 R data [kt 1yr 1] (1.14±0.21) 103 (403.69±64.97) 103 (102.20±1.46) 103 other expected backgrounds not shown - 1 year exposure - 0.4 ktons fiducial volume (50%) - detector resolution of 5%/ (E[MeV]). -11C background signal is obtained from KamLAND data extrapolation

pep neutrinos, 11C 11C decays are the major background in pep energy window Since they are produced by cosmic muons, the deeper the experiment the better the background KamLAND Borexino Eμ [GeV] 350 260 270 n12c[x1031] 4.54 4.30 (all C) 4.51 R data [kt 1yr 1] (1.14±0.21) 103 (403.69±64.97) 103 (102.20±1.46) 103 other expected backgrounds not shown Borexino - 1 year exposure 100 tons fiducial volume detector resolution of 5%/ (E[MeV]). data from arxiv:1104.1816v1

pep neutrinos, Impact on osc. parameters E range: 0.2-6.5 MeV, 50% FV Determine the survival probability according to the current solar best fit point: tan²θ12 := 0.468 Δm21² := 6.02 x 10-5 ev² sin²θ13 := 0.01 Adding 1 resp. 2 years of data to the other solar experiments (excl. latest Borexino) Significant improvement on sin²θ13

CNO neutrinos Improved models (2005) suggest 30% lower metallicity broken the previous excellent agreement between solar model calculations and helioseismology Astrophysical puzzle: Are elements homogeneously distributed in the Sun? CNO neutrinos can measure the metalicity of the core. BPS08 solar model: Peña-Garay and Serenelli arxiv:0811.2424

Geo neutrinos Anti-neutrinos from U-238, Th-232 and K-40 on Earth o 20% from mantle at o Check models of Earth heat production detection: anti-ve + p e+ + n Measured geo-neutrino flux: KamLAND2008 (25±9) ev/kt yr 1.6 Borexino (3.9 1.3 ) ev/0.1kt yr Expected geo-neutrino flux : 29 ev/0.78kt(lab) yr - 21ev/0.78kT(LAB) yr from reactor KamLAND: 32ev/1kT(CH2) yr 218ev/1kT(CH2) yr from reactor Borexino: 3ev/0.1kT(C9H12) yr 1.5 ev/0.1kt(c9h12) yr from reactor S. Enomoto XIII International Workshop on Neutrino Telescopes, Venice, March 10-13 2009 MULTI SITE MEASUREMENT

Reactor neutrinos Bruce Detection rate including oscillation Pickering Darlington

Reactor neutrinos Flux is 5 times less than KamLAND BUT reactor spectrum, including oscillations, have sharp peaks and minima, that increase the parameter-fitting sensitivity for Δm212 Bruce Pickering Darlington

Current Status By the end of the year (2011) Detector upgrade Cavity work, cleaning, PMT repairs Install hold-down rope system Install new calibration hardware Electronic update Next year(2012) Detector upgrade Install purification systems Commissioning Water fill and run Start scintillator fill 2013 Physics/Commissioning Start liquid scintillator phase

Summary is the follow up of the SNO experiment replacing the heavy water by liquid scintillator Liquid scintillator has a higher light yield than heavy water and allows to investigate the low energy region (E < 3.5MeV) Two phases of the experiment with different physical goals are planned: A liquid scintillator phase for the search of low energy solar neutrinos (pep, CNO) A Nd loaded phase for the search of neutrinoless double beta decay Other exciting physical goals are reactor oscillation confirmation, geo-neutrinos in a geologically-interesting location, supernova neutrino watch,... The main upgrades to the detector will be completed by the end of the year will start operation with water fill in the second half of 2012

BACKUP SLIDES

Location

Location @ SNOLAB: existing SNO facility Over 53,000 sq.ft. of climate-controlled class-2000 cleanroom laboratory space Scintillator purification Water plant Rail-car unloading terminal Storage tanks control room detector

SNOlab Inside SNOlab Outside SNOlab

Liquid scintillator LAB Purification strategies: Multi-stage distillation Initial LAB cleanup for high radio-purity and optical clarity Dual-stream PPO distillation for scintillator recirculation Pre-purification of PPO concentrated solution Steam/N2 stripping under vacuum Water extraction (liquid-liquid extraction) Effective for ionic metals (K, Pb, Ra) and limited efficiency for Th and Po Stable for PPO-LAB solutions Functional metal scavengers (R&D) High-flow columns effective for Pb, Bi and Ra