Modeling quasi-free neutrino-nucleus reactions for accelerator-based experiments
The discovery of neutrino flavor oscillations has triggered an unparalleled number of experimental propositions, aimed mainly at extracting all parameters in the neutrino mass mixing matrix. An important category of such experiments, the long-baseline accelerator experiments, studies interactions of neutrinos with the target material inside a near and a far detector. In addition, neutrino-nucleus reactions are at the center of attention in scattering experiments, such as MINERvA and SciBooNE. At typical few-GeV neutrino energies, the analyses of both types of experiments require a comprehensive knowledge of medium-energy neutrino-nucleus cross sections. In this dissertation, the focus lies on a theoretical description of neutrino-nucleus interactions in the 1-GeV energy range. At these energies, the nuclear response is dominated by quasi-elastic nucleon-knockout processes and Delta-mediated one-pion production. To compute the corresponding cross sections, a fully relativistic framework based on hadronic degrees of freedom is developed. The weak hadron couplings are modeled through weak vector and axial-vector form factors that are constrained by physical principles and experimental data. Within the relativistic Glauber model developed by the Ghent theory group, the influence of nuclear effects such as nuclear binding, medium modifications of Delta properties and final-state interactions is taken into account. We find that the existing large uncertainties on the axial form factors induce 20 to 30% variations in the cross sections. For the quasi-free reactions under study in this work, we conclude that nuclear effects are extremely large. Final-state interactions, for example, make that only about half of the pions and nucleons produced inside medium-sized nuclei effectively reach the detectors, the effect becoming even larger for heavier nuclei like iron. We study the possibility of extracting strangeness information by measuring ratios of quasi-elastic nucleon-knockout cross sections and find that some ratios are theoretically clean enough to determine a new value for the strangeness contribution to the nucleon spin. With respect to coherent pion production, we show that the widely-used local approximation is not valid for neutrino-induced reactions.
Physics and Astronomy, Delta production, quasi-elastic, nuclear reactions, nucleon knockout, pion production
Networked Digital Library of Theses and Dissertations