Utilising the upgraded T2K near detector and developing water-based liquid scintillator technology towards a CP violation measurement in neutrinos

The dominance of matter over antimatter in our universe is an unresolved question in our Standard Model of particle physics. Measuring Charge-Parity violation in neutrino oscillations at long-baseline neutrino experiments is crucial for understanding this phenomenon. The T2K experiment, which is currently operational, and its successor HyperKamiokande, beginning in 2027, are the most sensitive probes for measuring CP violation in neutrinos, and early hints of maximal violation have been published by T2K. There is a discovery potential with the data that will be taken in T2K over the course of this fellowship period if CP violation is indeed maximal, or with precision measurements to be performed using high statistics at HyperK. To achieve this in T2K its recently upgraded near detector, ND280, must be fully utilised, and for the high-statistics precision era in HyperK, further upgrades to ND280 will be needed. This project aims to characterise and maximise the performance of the upgraded ND280, using the state of the art Super Fine Grain detector and high-angle Time Projection Chambers that were installed with the final goal of reducing systematic uncertainties in neutrino measurements from ~6% to ~4%. The new detectors will be used to perform a measurement of the electron-neutrino cross-section to reduce this as a large systematic uncertainty contribution in CP violation measurements. This measurement will maximise CPV discovery potential in T2K, while the characterisation and methodology will be critical in HyperK to achieve a precision measurement faster. To reach systematic uncertainties below 3% in HyperK, research into using a large scale water-based liquid scintillator detector in ND280 will be undertaken, including building and characterising prototypes to then establish a sensitivity study for CP violation measurement in HyperK in the next decade.