SuperNEMO Commissioning and Sensitivity Demonstration

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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 totheir tiny mass differences. However, despite knowing rather precisely these mass differences, we still do not know what the absolute mass scale of theneutrino is. One of the highest priorities in particle physics today is to elucidate some of these mysteries surrounding the neutrino. This maygive us further insight into such fundamental questions as the nature ofphysics at the extremely high energies associated with Grand Unification,and the source of the matter-antimatter asymmetry which we observe in theuniverse today.Beta decay is a familiar radioactive process whereby a parent nucleusdecays into a daughter nucleus with the emission of an electron andan (unseen) anti-neutrino. In certain nuclei beta decay is forbidden but,very rarely, two simultaneous beta decays may occur. The distinctivesignature of two electrons being emitted has been observed in severalisotopes. We are searching for a distinct form of double-beta decayin which no neutrinos are emitted alongside the electrons, resulting inthe electrons carrying away the full energy of the associated nucleardecay. 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 greatersensitivity 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 leavein the detector. UK groups have been building this tracking detectorfor 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 anunderground laboratory located under the Alps between France and Italyin 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 andthe US. Extensive work will be required to carefully assemble thefirst module of SuperNEMO, called the "Demonstrator Module", such thatit works as expected and that no radioactive contamination is allowed to enter the detector. Even trace contamination, far below the level of radioactivityin ordinary materials, could completely swamp the very rare processes thatwe are searching for.By the end of this project, the SuperNEMO Demonstrator Module will beup and running and launching into an exciting physics program to tryto address some of the fundamental questions outlined above.