Transcript Neutrinoless Double Beta Decay with SNO+

Neutrinoless Double Beta Decay with SNO+
Jeff Hartnell for the SNO+ Collaboration
University of Sussex, UK
Neutrinoless Double
Beta Decay (0νββ)
Discovery of 0νββ is of key importance for
understanding the universe and would yield
answers to fundamental questions.
 Is the neutrino its own antiparticle?
 What is the absolute mass of the neutrino?
With the violation of lepton number it is
possible for two neutrons to simultaneously
decay into two protons plus two electrons and
no neutrinos.
The smallness of the neutrino mass
suppresses the rate of this process but also
gives a handle on that mass. The rate of
0νββ is given by
Experiment
Sensitivity
With 780 tonnes of linear alkylbenzene (LAB), the SNO+ detector in
Canada is one of the largest scintillator detectors in the world. Loading the
scintillator with neodymium at a fraction of one percent by mass provides a
tonne-scale experiment and a sensitive search for 0νββ will be performed.
With 0.3% loading of natural neodymium
SNO+ will contain 131 kg of 150Nd. Shown
below is the simulated spectrum expected for
an effective neutrino mass of 350 meV.
~9500 PMTs,
54% coverage
Acrylic vessel
12 m diameter
780 tonnes LAB
liquid scintillator
5700 tonnes H20
outer shielding
O(tonne) 0νββ
element/isotope
1700 tonnes H20
inner shielding
The major backgrounds are from 2νββ and 8B
solar neutrinos. 214Bi is shown with 99.98%
tagging efficiency and 208Tl with 90%.
SNO+ will be sensitive to 0νββ decays with a
half-life of 1025 years and the evolution of the
sensitivity to the effective neutrino mass is
shown below.
National Geographic
where T1/2 is the half-life, G is the phase
space factor, M is the nuclear matrix element
and m is the electron/effective neutrino mass.
The key experimental
signature for 0νββ is a
peak in visible energy at
the Q-value of the
nucleus, smeared by
detector resolution.
Features of SNO+
 Trade off energy resolution for
higher statistics.
 Cost-effective since the detector
already exists.
 Various isotopes can be used.
 Initial scintillator purification by
distillation.
 In-situ purification to further
remove backgrounds.
Background reduction
 Huge external shielding, 7400
tonnes.
 PMTs stand-off from scintillator.
 Self-shielding of the scintillator.
Schedule
 2012: construct scintillator
process systems, light water run.
 2013: scintillator phase begins.
Avenues for future upgrades
With R&D Nd enrichment and/or other
isotopes offer potential for significant
sensitivity gains.