The project focused primarily on the quasi-elastic scattering mechanism (a single nucleon knockout from a nucleus), a crucial process for the HyperK and DUNE experiments, addressing both medium and high energy transfer regimes. In the initial phase, we developed the spectral function for the 16O nucleus, with particular emphasis on assessing theoretical uncertainties arising from the reconstruction of spectral functions. To achieve this, we employed a novel method based on expanding the nuclear response using orthogonal polynomials.
This spectral reconstruction method was later applied to derive the spin response in infinite neutron matter, leading to the first consistent ab initio calculation of the nuclear response, enabling rigorous uncertainty quantification, and paving the way for further applications in astrophysical contexts.
The 16O spectral function was also validated against inclusive electron scattering data, with the associated theoretical uncertainties propagated to the observables. Additionally, the spectral functions were implemented into Monte Carlo event generators, allowing for direct comparison of theoretical predictions with neutrino scattering experiments.
The spectral function approach is based on impulse approximation. Within this approach, the final state interactions of the knocked-out nucleon are initially neglected and can be accounted for only in an approximate way. To achieve a fully consistent calculation, we employed the Lorentz Integral Transform (LIT) method, applying it for the first time to obtain the transverse response of the 40Ca nucleus. This development enabled a fully consistent prediction of the electron scattering cross-section and marked a critical milestone toward analyzing the 40Ar nucleus. Our calculations revealed an unexpected excess of strength compared to experimental data. We explored the source of this discrepancy by developing a Bayesian neural network that retrieves longitudinal and transverse responses from inclusive electron scattering cross-sections, trained on multiple light and medium-mass nuclei. This novel machine-learning approach lays the foundation for further advancements in understanding neutrino-nucleus scattering cross-sections. It also pointed out to some tensions between various experimental campaigns which collected data of 40Ca and so validates the LIT results which we obtained.
Finally, both the LIT and SF approaches, developed within the same many-body framework and nuclear dynamics, were employed to perform a comparative analysis of longitudinal and transverse responses for the 4He nucleus, enabling us to investigate the effects of final-state interactions and two-body currents.
Overview of Main Results
- Calculation of the spectral function for the 16O nucleus using a novel spectral reconstruction method, allowing for rigorous uncertainty quantification.
- Implementation of the spectral function into Monte Carlo event generators, directly impacting neutrino oscillation experiments.
- First ab initio calculation of the transverse response in a medium-mass system (40Ca), enabling accurate predictions of electron scattering cross-sections.
- Development of a novel machine-learning approach, based on a Bayesian neural network, to extract nuclear responses from electron scattering data.
- Creation of a framework to calculate spin responses in nuclear matter, with applications in astrophysics.
Dissemination
The results of this project have been published in three articles in high-impact, peer-reviewed journals, with three additional articles currently under review. Over the past two years, these findings were also presented at five international workshops and three conferences, where the Principal Investigator (PI) was invited to give talks.
The PI organized two international workshops directly related to the “NU 4 ν” project. The first workshop, "Neutrino Nucleus Scattering at Low and Intermediate Energies," was held at MITP (Mainz, Germany) in June 2023 and brought together experts from the theoretical and experimental neutrino scattering communities, along with developers of Monte Carlo event generators. A second workshop, "Uncertainty Quantification in Nuclear Physics," at MITP in June 2024, targeted the nuclear theory community. Additionally, the PI was involved in several conferences, including serving as a local organizer for the 25th European Conference on Few-Body Problems in Physics in August 2023 and acting as a convener for NuInt24, the leading conference series dedicated to neutrino-nucleus interactions.
The PI was also invited to give seminars and colloquia at several institutions and deliver lectures at summer schools for Ph.D. students (e.g. the ECT* Doctoral Program and the International Neutrino Summer School 2024). Furthermore, during the project, the PI was appointed a board member of NuSTEC (Neutrino Scattering Theory Experiment Collaboration), contributing expertise in many-body ab initio theory.
These activities enabled the dissemination of the project’s findings to a broad audience of researchers from various experimental and theoretical communities, primarily focused on nuclear and particle physics.
