Neutrino interactions, the Universe, and Everything

Neutrinos are the most abundant matter particle in the universe - around 100,000,000 pass through a person's thumbnail every second - but they very rarely interact with anything. This makes them difficult to study, and so neutrinos are one of the least-understood types of particle we know about. Despite this, neutrinos could be incredibly important to the makeup of our universe: some theories predict that differences in the physics of neutrinos and their antimatter equivalent, antineutrinos, could help explain why the universe is made of matter and not antimatter (or even why it exists at all). The big-picture aim of this project is to study the physics of neutrinos, and eventually to measure the differences between neutrinos and antineutrinos. We know about three "flavours" of neutrino (and antineutrino), named electron-, muon- and tau-neutrino, and we know that as a neutrino travels it can change flavour from one to another. This is understood theoretically through a process called "oscillation", and proving that it happens was one of the biggest discoveries of recent particle physics history, awarded the Nobel Prize in Physics in 2015. This fellowship will allow me to further our understanding of the universe with DUNE (the Deep Underground Neutrino Experiment), the future flagship neutrino oscillation experiment. DUNE aims to measure (and compare) the oscillation of neutrinos and antineutrinos with accuracy and precision that have never been achieved before. If we do see a difference, it could be one of the biggest particle physics discoveries of the century. Currently under construction, DUNE will use the world's most intense neutrino beam generated at Fermi National Accelerator Laboratory (FNAL) in Illinois. We will measure the neutrinos using an extremely sensitive "near detector" (part of which will be designed in this project) situated at FNAL - near to where the neutrino beam is created - to ensure we understand the types and energies of the neutrinos we have produced before they oscillate. The neutrino beam will then travel 1300 km towards South Dakota, where the neutrinos will be measured again by four large liquid-argon detectors, to see how many have changed to another flavour. One of the biggest challenges for DUNE's success will be understanding how neutrinos interact with argon nuclei. Because neutrinos are light, neutral particles they are impossible to see directly in particle detectors; we have to study them indirectly through the charged particles produced when a neutrino interacts with atoms inside the detector. A good understanding of how exactly neutrinos interact is therefore vital to answer deeper questions about the fundamental properties of these particles and how they might have impacted the evolution of our universe. DUNE uses a detector technology based on liquid argon; the way neutrinos interact with nuclei depends on the nucleus in question, in ways we don't fully understand, so studying interactions specifically with argon is crucial. This award will allow me to pursue a coherent two-part strategy to understand neutrino interactions for DUNE: first, by directly measuring different types of neutrino interactions in the existing MicroBooNE experiment (also using liquid argon); and second, by designing a new gaseous-argon component for the near detector for DUNE. MicroBooNE is currently the only liquid-argon detector taking data in a neutrino beam, so we have the unique opportunity to make many "first-ever" measurements of these processes, with high statistics, using the same nucleus and detector technology as DUNE. This will be extremely important for improving our understanding of neutrino interactions before DUNE begins taking data; once it does, the gaseous-argon detector will allow us to measure the particles produced by neutrino interactions in unprecedented detail, ultimately enabling DUNE to make new discoveries that will forever change the way we understand the world around us.