RA post request re Dave Wark's T2k spokesperson position

点击翻译按钮获取中文摘要

Over the last decade experiments throughout the world have demonstrated that the particles known as neutrinos have very different properties than was expected in the Standard Model of particle physics. In the Standard Model neutrinos come in three different kinds, called 'flavours' - electron, muon, and tau neutrinos - and these flavours are immutable. Once a neutrino is produced as one flavour it never changes. Standard Model neutrinos were also thought to have no rest mass, and therefore to always travel at the speed of light. We now know that neutrinos, in fact, have mass, and that the flavours of neutrinos can mix in a particular way we call 'neutrino oscillations' whereby a beam of one flavour of neutrino will turn into the other flavours as it propagates. The T2K experiment will make new measurements of unprecedented precision of these neutrino oscillations in the hopes of better understanding the phenomenon and also trying to understand the implications of neutrino oscillations for other areas of physics. In particular, neutrino oscillations are described by three mixing angles that effect how the different flavours mix with each other, and existing experiments have only measured two of these angles. It is the goal of T2K to observe effects arising from the third angle, and T2K should be about ten times more sensitive than existing experiments which have only set an upper limit on the size of this angle. This third angle is particularly interesting to physicists, because if it is non-zero it opens the possibility of observing violations of a symmetry called CP in neutrino oscillations. CP violation would make the oscillations of neutrino different from the oscillations of anti-neutrinos, and this effect may be related to one of the biggest mysteries in fundamental physics - why is there more matter than anti-matter in the universe? This CP violation is the target of the longer term plans for an ambitious facility called a Neutrino Factory, but since the third angle must be larger than zero for this to succeed a measurement of this third angle would be a key step forward in neutrino oscillation physics. T2K works by creating a powerful beam of muon neutrinos at the J-PARC facility on Japan's east coast and then allowing it to propagate through the ground underneath Japan to a huge underground detector called Super Kamiokande near Japan's west coast. Neutrino oscillations will make most of these muon neutrinos change flavour, and if the third angle is not zero some of them will turn into electron neutrinos which can be seen in Super Kamiokande. Detectors will be built at J-PARC to measure the properties of the neutrino beam before it propagates between the two facilities. The UK will contribute major elements of these near detectors at J-PARC (as well as elements of the neutrino beamline). The purpose of these near detectors is to make sure that we know how many electron neutrinos were in the beam to start with (you cannot make a pure muon neutrino beam, there is always some contamination) and how many interactions there are that might fool us into thinking there are electron neutrinos when there aren't. In order to perform the experiment these near detector measurements have to be compared to the observations by Super Kamiokande, and the RA requested in this grant would be in charge of the UK work on understanding and analysing the data from Super Kamiokande.