Search for Majorana Neutrinos with the SNO+ detector at SNOLAB
Amélia Maio (CFNUL/FCUL and LIP) on behalf of the SNO+ Collaboration
Calor 2014, Giessen, Germany, 8th April 2014 2 km !
SNOLAB in Canada is the second deepest underground lab in the world, so, with excellent background conditions.
Amélia Maio CALOR 2014 - Giessen, Germany 2 CALOR 2014, Gienssen – Germa Outline
Search for Majorana Neutrinos Anti-neutrinos from reactors Geo-neutrinos Solar neutrinos, supernova neutrinos
I will focus on the Search for Majorana neutrinos
are neutrinos their own antiparticles? is lepton number violated? what is the absolute neutrino mass?
Amélia Maio CALOR 2014 - Giessen, Germany 3 CALOR 2014, Gienssen – Germa From SNO to
9000 PMTs, in a structure with 17m diam.
Acrylic Vessel (AV): 12 m diameter
Liquid scintillator: 780 ton
New hold-down rope system to counter AV buoyancy
Water shielding: 1700 ton + 5300 ton
New calibration system
New readout system (20x faster) Amélia Maio CALOR 2014 - Giessen, Germany 4 CALOR 2014, Gienssen – Germa Liquid Scintillator: LAB+PPO
LAB (Linear alkylbenzene) with 2g/l of PPO (fluor 2,5-diphenyloxazole)
Chemically compatible with acrylic, high radiopurity
New purification systems – distillation, water extraction – presently being installed
Good optical transparency and low scattering (> 10 m, but lower when loaded) Safe: low toxicity, high flashpoint (150º) 3 developed by SNO+, Density =0.86g/cm => positive buoyancy in AV => used also in DayaBay rope hold-down system installed
New technique to load Tellurium, using telluric acid , water and surfactant 130 Te High light Yield (9400 emitted photons/MeV w/ 0.5% loading 200 detected p.e./MeV) ==> energy resolution of 4.5% at 2.5 MeV
Amélia Maio CALOR 2014 - Giessen, Germany 5 CALOR 2014, Gienssen – Germa Calibration
Optical Calibration (new) (see talk of Luis Seabra)
96 Optical led/plastic fibers for PMT response, time information, for position calibration.
20 quartz fibers for transparency
Laser Ball for synchronization of PMTs, position calibration, transparency, PMT response, but insertion less frequent.
Calibration with radioactive sources
Several radioactive sources being developed: AmBe (n, γ), 16N (γ), 24Na (γ), 48Sc(γ), 57,60Co (γ), 65Zn (γ), 90Y (β)
Naturally present backgrounds will also be extensively used: C14, Tl208, Bi214, Po-210, etc...
Amélia Maio CALOR 2014 - Giessen, Germany 6 CALOR 2014, Gienssen – Germa Now with liquid scintillator loaded with 130Te
Amélia Maio CALOR 2014 - Giessen, Germany 7 CALOR 2014, Gienssen – Germa Majorana Neutrinos and Double Beta Decay
Neutrinos are not A = 76 necessarily Dirac.....
Neutrinoless mode if neutrinos are Majorana For some even-even nuclei, usual β decay energetically forbidden, but not the double decay
35 naturally occurring isotopes can double beta decay
Observed in ~ 10 0νββ search in liquid scintillators
Idea: Dissolve isotope in liquid scintillator, calorimetric measurement R. Raghavan, Borexino yellow book(1991), PRL72, 10 (1994)
Large mass Poor energy resolution large volume detectors (as SNO), harder to distinguish bkg so large masses possible even at gamma lines small loading higher bkg from 2 neutrinos continuous spectrum Low background Choice of isotope intrinsic radiopurity very good fiducial volume rejection of Background from solar external backgrounds neutrinos purification of cosmogenically because detector mass activated contaminants >>larger than isotope mass for Q> 2 MeV, many backgrounds Can ultimately limit the can be identified with delayed sensitivity. Future detectors coincidence tagging will need directionality
Amélia Maio CALOR 2014 - Giessen, Germany 9 CALOR 2014, Gienssen – Germa Rate of neutrinoless double beta decay
Effective Majorana neutrino mass
Very low backgrounds required: Det. material contamination, cosmogenic activation, two-neutrino signal and … solar neutrinos (!) 0νββ search in SNO+
● Lower energy resolution than other ββ detector types ● BUT very high quantity of the isotope dissolved in active medium with low background ● Need to avoid degrading the energy resolution with the loading: tested Nd-150 (higher Q) and Te-130 (higher Nat. Ab.) (also Xe-136 tested and used in KamLAND-Zen)
2νββ [years] 0νββ [years] measured calculated by NEMO-3: by IBM-2: 18 23 Nd 9 x 10 (g.s.) 3 x 10 / 20 2 1 x 10 (e.s.) (Mββ [eV]) Te 7 x 1020 (g.s.) 4 x 1023 / 2 (Mββ [eV])
Amélia Maio CALOR 2014 - Giessen, Germany 11 CALOR 2014, Gienssen – Germa Double Beta Decay Background
2νββ: irreducible! (lower for Te) ● energy resolution is fundamental;position resolution also against pile-up Radio-purity of scintillator and Nd / Te loading cosmogenic activation of isotopes can be constrained in-situ (different loadings, purification) Bi-214, Bi-212 and Tl-208 rejected by α - β coincidences tagging
Solar B8 neutrinos are irreducible bckg but rate and distribution is known and high energy tail is visible Expected mass sensitivity Pre-loading pure-scintillator between 80 and 100 meV phase for tests 5 years of data taking @ 0.3% loading Amélia Maio CALOR 2014 - Giessen, Germany 12 CALOR 2014, Gienssen – Germa And now a little bit of anti-neutrinos
Amélia Maio CALOR 2014 - Giessen, Germany 13 CALOR 2014, Gienssen – Germa Anti-neutrinos νe + p → e⁺ + n
Positron annihilation gives anti-neutrino energy and interaction point Delayed neutron capture gives clear tagging and “smeared” direction
Almost background free & very high efficiency Geo (not to scale)
Contributions from: Reactors with oscillations - distant nuclear reactors - 3 Canadian reactors - geo-neutrinos from U/Th decay chains inside crust & mantle
Crust
Mainly energy, but reactor variations and directions to be explored
Mantle Amélia Maio CALOR 2014 - Giessen, Germany 14 CALOR 2014, Gienssen – Germa Status
Ropes basket in place Water in detector (16 ft. this week)
PMTs SNO+ fiber/LED people at Calibration work ongoing Summary and outlook
SNO+, a large volume liquid scintillator loaded with a large mass of 130Te will: Probe the nature and magnitude of the neutrino mass, with sensitivity about 100 meV Measure Anti-neutrinos from reactors and the Earth, Solar and Supernova neutrinos
SNO+ is almost ready for the water phase commissioning by the end of 2014: New PMT calibration system based on fibers and LEDs: installation almost finished New mechanism to insert the calibrations sources is designed and construction is starting at LIP workshops
SNO+, scintillator phase expected for 2015: Initially with unloaded scintillator 0νββ search with 130Te (0.3% loading, could be later increased to 3%)
Amélia Maio CALOR 2014 - Giessen, Germany 16 CALOR 2014, Gienssen – Germa Acknowledgements
My Thanks to José Maneira, Sofia Andringa and to Luis Seabra for helping me with these slides and the fruitful discussions to prepare my first public action in SNO+
Portuguese participation in SNO+ funded by FCT project PTDC/FIS/115281/2009
Amélia Maio CALOR 2014 - Giessen, Germany 17 CALOR 2014, Gienssen – Germa