Neutrino Scattering R&D for CP Violation Searches

The predominance of matter over antimatter in the universe points directly to the existence of some currently hidden laws of physics which are different for matter and anti-matter. One focus of the search for these new laws is the recently-discovered phenomenon of neutrino oscillations. Searching for these new laws of physics will require comparing the oscillations of neutrinos and anti-neutrinos. In neutrino oscillation, the internal quantum mechanical properties of neutrinos---specifically the mass and the flavour---interfere with each other. This allows a neutrino created as one flavour to be observed as another flavour. In the next generation of neutrino experiments, we will compare muon neutrino to electron neutrino oscillation to noun antineutrino to electron antineutrino oscillation. Doing so is the best way to explore charge-parity (CP) symmetry, which stipulates that antimatter should behave just like matter if viewed through a mirror and upside down. CP violation in neutrinos would manifest itself as antineutrinos oscillating differently than neutrinos, and if this happens it is a strong clue as to the origins of the matter/antimatter imbalance in the Universe today.

Neutrino oscillation measurements depend on accurate knowledge of neutrino interactions with the target nuclei used in neutrino detectors. This R&D is dedicated to developing a new type of neutrino detectors based on high pressure gas. This will allow us to look at neutrino-nucleus interactions in more detail than ever before, and will give us much more accuracy on neutrino oscillation measurements.

The High Pressure Time Projection Chamber (HPTPC) with optical readout is a new kind of particle detector, with original aspects that capitalise on cross-disciplinary progress and exchange of ideas. Examples of this include the TPC amplification region design, and the optical readout. The mesh amplification component is a particle-detection device invented by the DMTPC collaboration, made possible by new industrial techniques to produce large-area, precision mesh screens for applications from medical devices to filters for industrial production lines. In the HPTPC detector development effort, project members have collaborated across disciplines with a wide range of academic and industrial partners, for example Massachusetts General Hospital, the Raytheon Company, the MIT Institute for Soldier Nanotechnology, and Schlumberger in the US.
Supporting detector R&D is crucial for establishing UK leadership in the global particle physics programme of the future. The research proposed here is essential on the development path for the next generation of neutrino and directional dark matter detection experiments. Detector development has been the engine of progress in particle physics, and highly pixellated gas detectors have great potential to make precise measurements of new phenomena in the next decade. Experiments using or planning to use such detectors are pursuing some of the biggest questions in science today: testing the fundamental symmetries of nature using neutrinos (which is what this proposal is aimed at), and searching for interactions of the mysterious dark matter that makes up most of the matter in the universe.
Fundamental research into the nature of matter provides the foundation that underpins the technological development that continues to advance society as a whole. This research inspires scientific interest and training of students to think creatively, as well as to develop and apply analytical skills to difficult problems. These skills are widely necessary and appreciated by society. In addition to this non-specific but very real benefit, researchers in the fields of particle physics, nuclear engineering, and particle astrophysics will directly benefit. There are also potential technological spin-offs which would benefit society. These include applications in chemistry; biology; medicine; and national security applications in the areas of screening and non-proliferation.
The knowledge gained from the R&D proposed here would improve the systematic uncertainties on energy and position reconstruction for large neutrino detectors. In the near future, this would benefit the long baseline neutrino oscillation programme, and could also be applied to the search for dark matter. New discoveries in neutrino physics (or dark matter) would have huge scientific and societal impact, and spark broad media coverage and great public interest.