Using neutrinos to unravel the mysteries of the universe

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Neutrinos are the least understood particles we know of. They have extremely small mass and they rarely interact, yet they are extremely abundant and are critical for the evolution of our universe. Neutrinos come in three flavours (electron, muon and tau neutrinos), and since the 1990s we have known that a neutrino can change its flavour as it travels. There are still two big questions left to address about neutrinos. The first is that, surprisingly, we do not yet know which is the lightest neutrino. Finding that the third neutrino is heavier than the other two would give evidence for many Grand Unified Theories that seek to explain particle interactions as different manifestations of a single force. If that is not the case, the way we think about the natural forces in the universe will be completely changed. The second question is whether neutrinos and antineutrinos oscillate in the same way. Answering this question might solve one of the biggest mysteries about the origin of the universe: the Big Bang should have created equal amounts of matter and antimatter, but today, everything around us, from the smallest microorganism to the largest stellar object, is made almost entirely by matter. If neutrinos and antineutrinos oscillate following different rules, they might be the reason why the universe evolved to be dominated by matter rather than antimatter, hence allowing the existence of stars, planets and even us.This award will allow me to use a coherent strategy to solve these two mysteries, following the ambitious programme of the two experiments best equipped to answer them: NOvA and DUNE. NOvA is a world leading long baseline neutrino experiment: an intense beam of muon neutrinos is produced at the Fermi National Accelerator Laboratory (FNAL), near Chicago, and directed 800 km away towards Minnesota. NOvA uses a near and a far detector to measure the flavour of the neutrinos produced at FNAL, and the flavour of the neutrinos that arrive in Minnesota. DUNE is the future world flagship experiment for neutrino oscillation measurements, fully funded, approved by the US Department of Energy, and currently in the construction phase. DUNE will use the intense muon neutrino beam from FNAL and direct it 1300 km away towards South Dakota. DUNE will use a more powerful beam, a much bigger far detector, and better detector technology than NOvA.As neutrinos can only be detected when they interact with the matter in the detector and produce other particles, currently theoretical neutrino interaction models are the cause of the largest systematic uncertainties in neutrino oscillation analyses. High precision cross-section measurements of (anti)neutrino interactions and their products are essential for the precision measurements of neutrino oscillation parameters. My strategy is to perform such measurements using the high statistics accumulated by the NOvA near detector, and a prototype of the DUNE near detector. These results will directly impact both the NOvA and DUNE neutrino oscillation analyses. Additionally, I will lead the NOvA-T2K joint neutrino oscillation analysis. The main challenge of this analysis is presented by the very different neutrino interaction models that the two experiments use. Having made major contributions to neutrino cross section and oscillation analyses during my time on T2K, and currently leading the NOvA Beam simulation and data group, and also the NOvA near detector cross section group, I am uniquely qualified to lead and ensure the success of this joint analysis. This will be the most important neutrino physics measurement before the next generation experiments turn on. The experience and reputation gained during the NOvA years by my group at Bristol will ensure our leadership in the DUNE oscillation analysis too.This fellowship will allow me to establish and lead the neutrino group at the University of Bristol to be at the forefront of two extraordinary discoveries in neutrino physics.