SuperNEMO Commissioning and Sensitivity Demonstration

Lead Research Organisation: University College London
Department Name: Physics and Astronomy

Abstract

Neutrinos are the most abundant matter particle in the universe, and yet
our knowledge of them is still lacking in fundamental respects. We do not
know whether neutrinos and anti-neutrinos are really distinct particles, or
just different versions of the same underlying particle, which is possible
since they do not carry any charge. In recent decades neutrino oscillation
experiments have shed considerable light on the flavour structure of neutrinos,
and in particular how neutrinos may turn from one flavour into another due to
their tiny mass differences. However, despite knowing rather precisely these
mass differences, we still do not know what the absolute mass scale of the
neutrino is. One of the highest priorities in particle physics today is to
elucidate some of these mysteries surrounding the neutrino. This may
give us further insight into such fundamental questions as the nature of
physics at the extremely high energies associated with Grand Unification,
and the source of the matter-antimatter asymmetry which we observe in the
universe today.

Beta decay is a familiar radioactive process whereby a parent nucleus
decays into a daughter nucleus with the emission of an electron and
an (unseen) anti-neutrino. In certain nuclei beta decay is forbidden but,
very rarely, two simultaneous beta decays may occur. The distinctive
signature of two electrons being emitted has been observed in several
isotopes. We are searching for a distinct form of double-beta decay
in which no neutrinos are emitted alongside the electrons, resulting in
the electrons carrying away the full energy of the associated nuclear
decay. This "neutrinoless" process can only occur if neutrinos and
anti-neutrinos are the same fundamental particle. Moreover, by measuring
the rate of such decays we can effectively measure the absolute mass of
the neutrino.

In order to search for neutrinoless double-beta decay with greater
sensitivity then ever before, we have built what is essentially the
largest Geiger counter in the world. This so-called "tracker" for the
SuperNEMO experiment records ionisation left by the electrons from the
double-beta decay and allows us to visualise the tracks that they leave
in the detector. UK groups have been building this tracking detector
for the last 3 years, based on extensive R&D that took place before that.

The next phase for SuperNEMO is to take the UK-built tracker to an
underground laboratory located under the Alps between France and Italy
in order to shield the experiment from cosmic rays. There, we will
marry the tracker with the other components of the detector that
are being assembled by colleagues in France, Russia, the Czech Republic and
the US. Extensive work will be required to carefully assemble the
first module of SuperNEMO, called the "Demonstrator Module", such that
it works as expected and that no radioactive contamination is allowed to enter
the detector. Even trace contamination, far below the level of radioactivity
in ordinary materials, could completely swamp the very rare processes that
we are searching for.

By the end of this project, the SuperNEMO Demonstrator Module will be
up and running and launching into an exciting physics program to try
to address some of the fundamental questions outlined above.

Planned Impact

Although our objectives are largely scientific in nature, our
work will have wider impact, including:

- industry. The SuperNEMO project members maintain close
links with a number of companies including but not limited to
Hamamatsu (Photomultiplier manufacturer, Japan), ETL
(Photomultiplier manufacturer, UK), ELJEN (scintillator
manufacturer, US) and ENVINET (scintillator manufacturer, Czech
Republic). We will maintain these links, continuing to test
new products and provide feedback to manufacturers where
appropriate.

- security applications. Members of the UK SuperNEMO collaboration
have used their experience to propose and develop two prototype
detectors that use cosmic rays to passively monitor volumes for
the presence of suspicious materials. We will continue to work
on potential applications of technologies related to the
SuperNEMO project.

- society at large. We plan a media campaign to coincide with
the start of SuperNEMO operations. SuperNEMO provides
visually striking images of double-beta decay due to the
full event reconstruction that it performs. We are also filming
various construction activities, anticipating their
use in future public presentations. We believe that raising
the media profile of SuperNEMO will complement other particle
physics news stories in the media and help to maintain the
interest of the public and in particular school students who
may be thinking of studying physics at university.

See "Pathways to Impact" for further information.

Publications

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Arnold R (2019) Detailed studies of $$^{100}$$Mo two-neutrino double beta decay in NEMO-3 in The European Physical Journal C

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Barabash A (2017) Calorimeter development for the SuperNEMO double beta decay experiment in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

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Cascella M (2016) Construction and commissioning of the SuperNEMO detector tracker in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

 
Description In the UK, we have built an ultra-low radioactivity tracking detector for SuperNEMO, obtaining world-leading low levels of radon and other impurities. This is a step toward proving the viability of this detection technique for the next generation of neutrinoless double-beta decay experiments.
Exploitation Route Many of the techniques developed in this project will have applications in low-background physics, such as the search for neutrinoless double-beta decay and dark matter. There may be applications to other fields of physics as well as beyond.
Sectors Education

 
Description The progress of the SuperNEMO project featured in an article appearing in The Guardian newspaper in October 2015, following the successful transport of the first tracker module from the UK to France. There was also coverage of the SuperNEMO Demonstrator Module inauguration event in November 2017.
First Year Of Impact 2015
Sector Education
Impact Types Cultural,Societal