1. The SNO+ Experiment: Overview and Status
DPG Spring Meeting Dresden 2013
Arnd Sörensen, Valentina Lozza, Nuno Barros, Belina von Krosigk, Laura Neumann, Johannes Petzoldt, Axel Boeltzig, Felix Krüger and Kai Zuber

2. Outline SNO+ = SNO + Liquid Scintillator ? Phases of Operation
From SNO to SNO+
Phases of Operation
Neodymium loaded Phase (0νββ with 150Nd)
Pure Scintillator Phase
TU Dresden
Summary & Outlook

3. Location @ SNOLab in Creighton Mine, Sudbury, Canada
deepest underground laboratory
2 km ≈ 6000 meter water equivalent flat overburden
muon rate:

4. Detector acrylic vessel 780 t liquid scintillator (LAB)
12 m diameter
5 cm thickness
780 t liquid scintillator (LAB)
≈ 9100 PMTs in support structure (~ 54% coverage)
light-water shielding:
1700 t inside
5700 t outside
urylon liner and radon seal

5. Linear Alkyl benzene (LAB)
LAB + PPO + (Nd)
fluor: 2 g/L PPO (= 2,5-Diphenyloxazol)
chemically compatible with acrylic
long scattering length & high optical transparency
high light yield (≈ 10,000 photons/MeV)
high purity available
inexpensive & safe

6. from SNO to SNO+ SNO SNO+ LAB lighter than water: rope hold up system
+ rope hold down system

7. from SNO to SNO+ General rope-net hold down system
new calibration (source manipulation) system
scintillator purification plant

8. from SNO to SNO+ Electronics DAQ boards refurbished improved data flow
replace & repair broken PMTs
PMTs remapped

9. from SNO to SNO+ Calibration new low energy sources
optical calibration via fibre-injected lasers and LEDs
variety of gamma, alpha, beta and neutron sources

10. (neutrinoless-) double beta decay
Phases of Operation
detector commissioning
water phase
150Nd loaded into liquid scintillator
reactor-, geo- and supernova- neutrinos
(neutrinoless-) double beta decay
search for solar neutrinos: pep and CNO
pure scintillator
2013
2014 -
2017/?
short pure scintillator phase
2017 - ?

11. Neodymium loaded Phase
large isotope mass, low background
poor energy resolution
neutrinoless 0vββ search with liquid scintillator
150Nd
high Q-value: MeV  low background
fastest calculated decay rate
complementary to other 0vββ experiments (76Ge, 136Xe …)
in SNO+
LS successfully loaded with Neodymium
0.1% loading
optimisation: 0.3% loading

12. Neodymium loaded Phase
0.1% Nd loading
(43.7 kg 150Nd)
mee = 350 meV
6.4% MeV
IBM‐2 matrix element
3 years running and
50% fiducial Volume
(≈ 0.4 kt)
Borexino background levels + efficient tagging:
214Bi: 99.9% reduction
208Tl: 90.0% reduction
Plot: Borexino Backgrounds + Nd Backgrounds + tagging
Pile-Up: usually Nd2v + 144Nd …
Background despite low Q-value through pile-up of e.g. 144Nd, 176Lu, 138La, 14C
99% pile-up rejection while keeping 90% signal in ROI

13. 0vββ with 150Nd Claim of Klapdor mee ≈ 170 – 530 meV
[Nucl. Phys. B. (Proc. Supp.), S143:229, 2005]
0.1% Nd (6.4% 3.37 MeV)
0.3% Nd (9.0% 3.37 MeV)
assuming Borexino background levels are reached and efficient tagging:
214Bi: 99.9% reduction
208Tl: 90.0% reduction

14. Solar Phase Complete our understanding of the solar neutrino fluxes:
Super-K and SNO measured 8B neutrinos
Borexino measured 7Be and first probed pep neutrinos
pp was observed with Ga experiments
improve pep measurement
still missing CNO (probe for solar metallicity)

15. pep Neutrinos single energy: 1.442 MeV
very well predicted flux (≈ 2% uncertainty)
new physics models (NSI) predict different survival probabilities in vacuum matter transition regions
SNO, [arXiv: ]
[PLB 594, (2004)]

16. CNO Neutrinos old (high Z) new (low Z)
[Peña-Garay & Serenelli, arXiv: ]
photospheric absorbtion lines/abundances
S-Factors
3D hydrodynamic models of near surface convection
No direct observation of CNO neutrinos yet !
probe for solar core metallicity
new solar physics developments suggest 30% lower metallicity

17. Reactor Neutrinos BUT Flux is 5 times less than KamLAND
no Oscillation 308 events
no Oscillation 1186 events
Oscillation 176 events
Oscillation 710 events
Flux is 5 times less than KamLAND
BUT
SNO+ reactor spectrum, including oscillations, have sharp peaks and minima, that increase the parameter-fitting sensitivity for Δm12

18. Geo Neutrinos
Signal:
from β-decays in Earth’s mantle and continental crust (238U,232Th,40K)
local region extremely well studied due to mining
low reactor-v background in SNO+: Reactor/Geo ≈ 1.1
check Earth heat production models / chemical composition (multi-site measurement in combination with Borexino, KamLAND)
Multi Site measurement
disentangle crust and mantle component

19. SNO+ @ TU Dresden 0vββ Phase pure scintillator phase
design, development and test of 48Sc calibration source (3.33 MeV - ROI)  T – Axel Boeltzig
study of cosmogenic (n,p)- activation of Nd and LAB
first measurement of natNd(p,x) cross sections [PRC 85, (2012)]
study of underground- and thermal- neutron activation of Nd
pure scintillator phase
sensitivity study to solar neutrinos and neutrino oscillation parameters
design, development and test of 57Co low energy (122 keV) calibration source
to test the detector threshold and the low energy response
alpha and proton quenching factor measurements [arXiv: ]
cosmogenic muons and muon induced background tagging
investigation of the 14C background

20. SNO+ will be filled with water this year 0vββ search starts next year
Summary
SNO+ succeeds the SNO experiment by replacing heavy water with liquid scintillator
LS has higher light yield and lower threshold allows to investigate lower energy range ( E < 3.5 MeV )
two phases planned:
Nd loaded phase to search for 0vββ decay of 150Nd
pure scintillator phase to observe pep and CNO solar neutrinos
reactor neutrino oscillation confirmation, geo neutrino investigation at geologically-interesting site, supernova neutrino watch …
SNO+ will be filled with water this year
0vββ search starts next year

21. Thank you for your attention !

22. more

23. pep, CNO Neutrinos - background
radio purity:
14C is not a problem  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  pep signal is at higher energy
SNO+
Borexino
Factor ~100 less muons from Borexino to SNO+
pep possible right away due to depth and size
CNO possible if 11C tagging effective
SNO+:
0.4kton (50% fid. volume)
1y exposure
5% E resolution
Borexino:
100t
CNO
pep
CNO
11C
11C
pep

24. Solar Phase
p-p solar fusion chain
CNO cycle

25. Assuming Borexino-level backgrounds are reached
Sensitivity Goals
(stat)
1 year
2 years
pep
9.1%
6.5% 8B
7.5%
5.4%
7Be 4%
2.8% pp
A few %?
CNO
~ 15%?
Assuming Borexino-level backgrounds are reached

26. pep sensitivity as a function of run time
Assuming Borexino-level backgrounds are reached