Neutrino interactions in the GeV regime

Our universe is dominated by matter over antimatter, and yet the laws of physics seemingly regards matter and antimatter almost the same. The matter dominance of the universe is conjectured to have resulted from processes violating the combined symmetry of charge conjugation and parity---a symmetry under simultaneous charge flip and mirror inversion---at extreme conditions in the early universe. The violation of this symmetry (CP violation) does exist at a small level and has been measured in microscopic systems that consist of quarks and antiquarks. However, the effects were found to be a dozen orders of magnitude too small to account for the matter-antimatter asymmetry. A new source of CP violation could be found with neutrinos (leptonic CP violation, LCPV). Different types (flavours) of neutrinos mix and the flavour composition of a given mass state can vary during propagation, hence neutrino oscillations. In neutrino oscillation analysis, LCPV can be identified with the difference between the oscillation probabilities of the neutrino and the corresponding antineutrino. This is the main goal of current and next-generation experiments such as T2K and DUNE, respectively.

Neutrinos and antineutrinos can be generated by accelerators, but we can only make detectors out of matter, not antimatter. The interactions of neutrinos and antineutrinos with matter are different even in the Standard Model. To detect the very delicate LCPV signature, these interactions need to be understood very precisely. The effects associated with nuclear targets are complex, leading to significant uncertainties. Because of the importance of nuclear effects in neutrino-nucleus interactions, recently various measurements have been performed by MINERvA and T2K, the two world-leading experiments on neutrino interactions. To significantly contribute to the global effort in understanding the matter-antimatter asymmetry of the present universe, I propose to work on cross section measurements in MINERvA and T2K, to systematically study neutrino interactions to provide the crucial input for future long-baseline neutrino oscillation experiments. I also propose to work on pioneering R&D for the DUNE High Pressure Gas Time Projection Chamber project, which could significantly improve the precision of the LCPV measurements, and greatly add to the science of DUNE.