Seed Corn Funding for Braidwood Project

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Neutrinos are governed by the weak nuclear force and form part of that fundamental class of particles called leptons. They come in three 'flavours' which are each paired with the electron, muon and tauon particles, respectively. We now know, however, that this classification is not as simple as it seems. Neutrinos also have mass (previously thought to be zero), but these masses do not directly correspond to those of the three neutrino flavours. Instead, a neutrino of a given flavour (like the electron-neutrino) can be viewed as a mixture of different neutrino mass states. This property allows neutrinos to apparently change or 'oscillate' between different types. A similar mixing phenomenon has long been known to exist among the quarks, though, at first glance, through a somewhat different mechanism. One of the many surprises is that the mixing amongst neutrinos is much larger than amongst the quarks. Nevertheless, theorists hope that the mixings in the two classes of particles can yet be related through some 'Grand Unified Theory' that brings together quarks and leptons, though the ability to do this straightforwardly will hinge on the value of a final mixing parameter which has not yet been determined. This parameter is known as 'theta13.' The oscillation relevant to theta13 may be affected as the neutrino state passes through matter and, if this were observed, it could be used to resolve the ordering of the neutrino mass states. Furthermore, it turns out that a third mixing angle would also allow some particle and anti-particle interactions to proceed at slightly different rates giving rise to 'CP-violation,' as for quarks. If the effect for leptons is large enough, it might explain the very existence of all the matter we see today. Therefore, the measurement of this third mixing angle and any associated CP-violation is an important next step. The first priority is to make a precise measurement of theta13, independent of these other possible effects. This is of fundamental interest in itself, and would also then allow other experiments (such as the planned T2K and NOvA projects) to look for CP violation and matter effects in the most sensitive and unambiguous manner. One of the best approaches to doing this is by looking for the apparent disappearance of anti-electron-neutrinos, produced in a nuclear reactor (due to their oscillations). Based on current experimental data, the distance scale over which this theta13 oscillation should occur is just under 2 kilometres from the reactor core. The challenge is that the size of the effect is expected to be only about 1 percent of the total, detectable neutrino flux - requiring a level of detection unprecedented for neutrino experiments. It is this measurement which the Braidwood project intends to carry out.