Leptonic CP violation: understanding the matter-antimatter asymmetry in the universe

Our current understanding of physics does not explain why the universe around us is made overwhelmingly of matter and not antimatter. My work on the T2K experiment, which studies the oscillations of a type of particle called the neutrino as it travels long distances, has seen hints of a new type of matter-antimatter difference which has the potential to provide an explanation for the matter dominated universe. Larger datasets and smaller uncertainties are necessary to confirm these differences. My fellowship will address both of these issues.

During the fellowship, the currently running long distance neutrino oscillation experiments, T2K and NOvA, will collect their largest neutrino-oscillation datasets to date. I will lead the analysis of T2K's data, which will, for the first time, be sensitive enough to provide highly significant evidence for matter-antimatter differences in neutrinos. As well as using the larger dataset, I will add new samples of neutrino events to the analysis, increasing the number of neutrino interactions that can be studied by approximately 30%. Not only will these new samples further increase the size of the available data, they will also give us a better understanding of how neutrinos interact with our detectors, allowing us to reduce the uncertainties in our analyses due to our knowledge of neutrino interactions. The resulting analysis will be the most precise constraint on matter-antimatter differences in neutrinos from any single experiment.

Currently T2K and NOvA analyse their data separately. This separation means that information that each experiment has that would improve the other's analysis is ignored. During this fellowship I would work with collaborators in the NOvA experiment to analyse T2K and NOvA data together for the first time. The result will be a more precise constraint on matter-antimatter differences in the neutrino sector than either experiment could produce alone, maximising the impact of these UK government funded experiments.

The billion-dollar scale DUNE experiment, which is scheduled to start taking data in the mid 2020s, promises even larger neutrino oscillation datasets than those from T2K and NOvA. However, our current understanding of neutrino interactions with our detector materials is not good enough to take advantage of these datasets. I will develop part of a High-Pressure gas Time Projection Chamber (HPgTPC) for DUNE that will measure neutrino interactions of a type inaccessible to previous detectors. The resulting reduction in our uncertainties on neutrino-matter interactions will give DUNE the capability to definitively observe and fully characterise the neutrino matter-antimatter asymmetry. In the long term there are potential medical applications of this type of detector in better understanding how radiation is deposited in materials, such as those used in radiotherapy.

The subsystem that this fellowship will allow me to lead the construction of is the HPgTPC's data acquisition (DAQ) electronics. DAQ electronics allow the HPgTPC to record the neutrino interactions of interest. To do this, I will use high-speed FPGA electronics which have wide applicability both within STFC's science area and more widely including the medical sector, fintech and national security. Furthermore, UK companies will be able to manufacture parts of the system, furthering the UK's high-tech sector. I will also lead a program of prototype tests of the HPgTPC in beams of low energy particles. These tests will allow the detector to be accurately calibrated and improve our knowledge of the interaction of these low energy particles with a variety of different materials. A reduction of DUNE's analysis uncertainties from 3% to 2% will correspond to a 33% reduction in the running time necessary to achieve definitive observation of matter-antimatter asymmetry in the neutrino sector, allowing us to do more physics with the same amount of funding.

Understanding the matter-antimatter asymmetry of the universe is a key priority for UK science, having been identified as one of the STFC's science challenges. The European particle physics strategy lists investigating the matter-antimatter asymmetry of the universe with neutrino oscillations as a scientific activity of the highest priority. Major participation in future experiments, such as DUNE, is highlighted. This proposal will have significant impact on this physics and construct a major hardware component of DUNE, thereby furthering UK innovation leadership.

This proposal will produce the world's best constraint on the matter-antimatter asymmetry in neutrino oscillations by adding new samples to the T2K experiment's analysis. The constraint will be improved further by analysing data from T2K together with that from the other currently operating long-baseline neutrino experiment NOvA, giving the best constraint from this generation of experiments. Designing a major hardware component for the next generation DUNE experiment will position my group to produce the most precise measurement with the next generation of experiments. These results will lead to talks at major international conferences, such as NEUTRINO and NuFACT, and at least one paper per year, each containing the world's most precise measurement of leptonic CP violation. The statistical analysis experience the post-doctoral researcher and any students who work on the project will gain through working on the analysis of T2K, NOvA and DUNE data will enable them to contribute to the UK's growing data science industry.

The high-pressure gas time projection chamber (HPgTPC) detector, that I will construct a large component of, will measure particles in energy ranges that are not accessible to current neutrino detectors. This will not only change the way oscillation physics is done by improving the uncertainties we have on how neutrinos interact with our detector materials but will improve these uncertainties for other areas of physics such as dark matter experiments. This improved understanding will be fed back to the nuclear physics community through established channels, such as the NuSTEC group.

Long term, HPgTPCs have potential medical applications in tracking low energy particles such as those used in radiotherapy through various materials. I will develop this impact by working with the members of the Imperial high energy physics group working on proton cancer therapy to identify appropriate medical industry partners, thereby benefitting both industry and the wider public.

There is benefit to the UK industrial community. The HPgTPC's electronics will use FPGAs, which offer programmable high-speed parallel computing. Imperial works on FPGA development with UK industry, including Maxeler, who develop tools to make the programming of FPGA electronics easier. This collaboration will be strengthened through the work in this proposal. FPGAs have applicability both within UKRI's science areas and more widely, including the medical sector, fintech and national security. Training students and the post-doc in their use will allow them to contribute to a better qualified workforce and improve UK leadership in those industries after their PhDs.

There is educational impact, through encouraging young people to take up STEM education. I am part of a team that takes a demonstration particle accelerator to schools. The demonstrator uses ping-pong balls and electronically controlled flippers to show the importance of timing in particle acceleration. I will take the demonstrator to local school careers evenings and science fairs and demonstrate it to the public at an 'Imperial lates' stall, where scientists demonstrate their work to the public in an informal evening setting. I will continue my involvement in Imperial's high energy physics masterclass where A level students come to Imperial to learn about particle physics through lectures and interactive workshops.