nuPRISM: An experimental method to remove neutrino interaction uncertainties from oscillation experiments

Abstract:  Future experiments propose to make precision measurements of parameters in the neutrino mixing matrix, including the possibly maximal mixing angle theta23, and an unknown CP violating phase, dCP, by comparing the event rate of neutrinos and antineutrinos observed close to, and far from the source. Such 'near to far' extrapolation methods must achieve percent level understanding of neutrino and antineutrino interactions, in order to relate experimental observables to the oscillation probability, which depends on the neutrino energy. However, recent developments over the last 5 years demonstrate that our understanding of neutrino interactions is insufficient. In particular, the interaction of neutrinos on correlated pairs of nucleons has only recently been added to neutrino interaction simulations. The misidentification of these processes as interactions on a single nucleon result in significant bias to the measured mixing parameters, even when near detector information is included in the analysis. Furthermore, the rate of this process is not well characterized, with notable differences between models. A novel new near detector technique, nuPRISM can address uncertainties in the neutrino interaction models. The detector combines measurements of multiple neutrino fluxes to create a pseudo mono-energetic neutrino beam. Measurements of this flux provide a direct relationship between the neutrino energy and experimental observables, and minimizes neutrino interaction model dependance. This seminar will discuss the near to far extrapolation methods employed by current oscillation experiments with the T2K experiment as an example, the issues related to neutrino interactions which are relevant to future measurements of theta23 and dCP, and how the nuPRISM technique can be used to mitigate these issues.