A search for sub-dominant neutrino oscillations and measurement of the third neutrino mixing angle, theta13, with the Double Chooz experiment

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What are neutrinos? Neutrinos are fundamental particles of Nature and despite being one of the most abundant particles in the Universe, the first observation of a neutrino was only 50 years ago. This highly elusive nature of neutrinos comes from the fact that they hardly ever interact with anything around them. Douglas Adams once described the chance of a neutrino interacting as it passes through the Earth as being 'roughly comparable to that of dropping a ball bearing at random from a cruising 747 and hitting, say, an egg sandwich'. Neutrinos weigh at least a 1/4 of a million times less than the electron, which is the next lightest particle and they could be much lighter still. It is widely believed that there are many fascinating facts about neutrinos yet to be discovered. This research proposal is about trying to understand and learn more about the special nature of neutrinos. There are three types of neutrino that have been directly seen but there could be more. In the last decade scientists have made a remarkable discovery: that a neutrino born as one type of neutrino can change in to one or both of the other two types of neutrino. But what's really interesting is that the neutrinos change, and then change back, repeatedly. This changing back and forth has been dubbed neutrino oscillations because it happens regularly like the swinging of the pendulum in a grandfather clock. Furthermore, it turns out that Nature only allows a certain fraction of the neutrinos to undergo these changes at any one time. Whether it's 50% of the neutrinos oscillating back and forth between the three types or just 5%, that is a fundamental parameter of Nature and it is the aim of this research proposal to measure that number. A strong source of neutrinos is a nuclear power station and you can detect the neutrinos from a long way away. The walls of the power station are almost completely transparent to the neutrinos and they pass straight through. You can imagine the neutrinos coming from the power station much like the light coming from inside a glass light bulb: it shines out in all directions. Vast numbers of neutrinos are emitted by the power station: around 1000 billion billion are produced every second. The experiment in this research proposal will be located about 1 km from the power station and it will detect only about one hundred neutrinos out of the billions passing through every 24 hours. If the neutrinos detected in this experiment were found to be changing type then it would be a tremendously important discovery. This is true not only because a fundamental constant of Nature would have been measured for the first time but it would also tell us whether neutrinos might hold the answers to a long outstanding mystery, namely where all the anti-matter in the Universe has gone. The Universe today is filled with matter and very little antimatter. But when it was formed in the Big Bang, equal amounts of matter and antimatter were made. Exactly what happened to all the antimatter is an intriguing puzzle and it is possible that by learning about neutrinos we will find the answer. If this experiment sees neutrinos from the power station oscillating then that will tell us whether it's possible for the behaviour of neutrinos and anti-neutrinos to be different. Thus, through studying neutrinos, we may have the beginnings of an answer to one of the big mysteries of the Universe.