Neutrinos are ghostly particles that change identity as they travel, and two giant experiments in the United States are now hunting for answers to why the universe is made of matter at all. The problem is that the Big Bang should have produced equal amounts of matter and antimatter, which would have annihilated each other, leaving nothing behind. Yet everything around us is matter. Neutrinos and their antineutrino counterparts might behave differently—oscillating between flavours under different rules—which could explain that imbalance. A second mystery is which of the three neutrino types is the lightest, a detail that would upend or confirm theories that unify the fundamental forces. This fellowship supports work on the NOvA experiment, which fires neutrinos 810 kilometres from Illinois to Minnesota, and the future DUNE experiment, which will send them 1,300 kilometres to South Dakota. The researcher’s team is improving how neutrino interactions are measured and developing new statistical tools to extract oscillation parameters from the data. This is fundamental science. It will not produce a practical application tomorrow. But understanding why matter dominates over antimatter addresses one of the deepest questions about why the universe—and we—exist at all.
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Neutrinos are the least understood particles we know of. They have extremely small mass and rarely interact, yet they are extremely abundant and critical for our universe's evolution. 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. This phenomenon is called neutrino oscillations. 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 have implications for many Grand Unified Theories that seek to explain particle interactions as different manifestations of a single force. If that is not the case, how 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 universe's origin: 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 allowed me to use a coherent strategy to start solving these two mysteries, following the ambitious programme of the two best equipped experiments 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 810 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. It is fully funded, approved by the US Department of Energy, and currently in construction. 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. While the first part of the fellowship focussed on making neutrino interaction measurements, the renewal proposal focusses on their impact on neutrino oscillation analyses and the development of specific techniques for measuring neutrino oscillation parameters. As neutrinos can only be detected when they interact with the matter in the detector and produce other particles, theoretical neutrino interaction models are currently the cause of the most significant systematic uncertainties in neutrino oscillation analyses. My strategy is to exploit the measurements made during the first part of the fellowship to make these experiments more sensitive to neutrino oscillation parameters - my team and I will do this both within the NOvA experiment and the NOvA-T2K joint oscillation analysis. With significant more data than the previous version of these analyses, these experiments have the potential to understand which neutrino is the lightest. Focussing on the future of neutrino experiments, my team and I will develop a new statistical technique to extract neutrino oscillation parameters, to ensure we hit the ground running once DUNE starts taking data. Finally, we will play a leading role in the installation of the DUNE far detector and perform checks to ensure the data taken is of the highest quality. All of these objectives will ensure that my team and I are at the forefront of these neutrino ground-breaking discoveries.
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