Neutrinoless double beta decay with SNO+

Transcription

1 Neutrinoless double beta decay with SNO+ - 0!"" with SNO+ - Backgrounds - Schedule Freija Descamps for the SNO+ collaboration 1

2 SNO+ detector 6000 m.w.e Deck with DAQ SNO+ operator ~780T LAB liquid organic scintillator +WLS acrylic vessel 12m 5cm thick ~9500 PMTs 54% coverage ~7kT ultrapure water shield rock 2

3 Liquid scintillator Solvent: Linear AlkylBenzene (LAB) Long attenuation length Safe: low toxicity and high flash point Chemically compatible with acrylic #-" separation through decay-time High light yield ~10000γ/MeV Wavelength shifter Petresa plant Bécancour, QC NIM A640, (2011) 3

4 0νββ with the SNO+ detector 6000 m.w.e ~780T LAB liquid organic scintillator + WLS acrylic vessel 12m 5cm thick ~9500 PMTs 54% coverage ~7kT ultrapure water shield Deck with DAQ rock SNO+ operator Neutrino-less double beta decay (add ~800kg of 130 Te) SNO+ approach: Trade-off energy resolution for higher statistics Low backgrounds External shielding Scintillator self-shielding LAB purification by distillation Re-use existing detector Scalable 4

5 130 Te advantages 34% natural abundance Load high amount of natural isotope Relatively inexpensive compared to enriched isotope 2!"" rate is relatively low (~100 times lower than 150 Nd) Lower background Less sensitive to poor energy resolution Improved optical properties No inherent optical absorption lines Higher intrinsic light yield Nd-LS (0.5%): 8400γ/MeV Te-LS (0.5%): 9400γ/MeV Te loaded LS scaled PMT response Nd loaded LS 5

6 Te loading Old loading technique Dissolve telluric acid (H6 O 6 Te) in water Combine with LAB using a surfactant Good optical properties Stable > 1 year explicitly demonstrated for 0.3% loading New loading technique (M. Yeh et al., paper in progress) 6

7 Backgrounds 39 Ar 210 Bi 11 C 14 C 40 K 85 Kr 210 Pb 210 Po U chain Th chain Cosmogenic e.g. 11 C, 60 Co External AV, PMTs, H2O, ropes Internal LS,surfactant, water, AV leaching, internal ropes 7

8 U and Th chains LS target level ~2.5 x g U /g cocktail ~3 x g Th /g cocktail Direct background # and " emissions Purification techniques Coincidence techniques are under investigation, ex.: "-# 214 Bi- 214 Po "-# 212 Bi- 212 Po #-" 212 Bi- 208 Tl % rejection 2.6 MeV gamma from external 208 Tl suppressed by fiducialization 8

9 Cosmogenic isotopes Short and long living isotopes can be produced by cosmogenic activation of natural tellurium. Isotopes (Q> 2 MeV, T1/2 > 20 days) rates from ACTIVIA, sea level (n,p)-flux from Armstrong and Gehrels. for E<200 MeV: TENDL database for cross-sections. Necessary purification factors have been determined. 2 stages: Above ground: 2 passes Dissolve Te(OH) 6 in water Re-crystalize using nitric acid Rinse with ethanol Below ground: 2 passes Dissolve in 80 C water Cool down to re-crystalize thermally 50% yield 3-6 months cool-down >10 4 reduction >10 2 reduction => Cosmogenic isotopes are negligible 9

10 SNO+ spectrum 3.5m (20%) fiducial volume cut x50 reduction in 212 BiPo 2 years <m! >=200 mev > 99.99% efficient 214 Bi tag 97% efficient internal 208 Tl tag Negligible cosmogenic isotopes 10

11 Conclusion SNO+: a large liquid scintillator approach to 0!"" Natural Te will be added to the liquid scintillator 0.3% loading (~800kg 130 Te) Possibility of increased loading Schedule Water level just below PMTs: now. Larger scale Te(OH)6 purification test: ongoing. Order for initial Te(OH)6 production: imminent. Completion of water-fill: end of Water running: start of Scintillator transition: mid Introduction of Te: end of 2014/start of

12 Thank You 12 water level currently at 9ft (2.75m)