NuSTEC White Paper: Status and Challenges of Neutrino-Nucleus Scattering

Abstract: The precise measurement of neutrino properties is among the highest priorities in fundamental particle physics, involving many experiments worldwide. Since the experiments rely on the interactions of neutrinos with bound nucleons inside atomic nuclei, the planned advances in the scope and precision of these experiments requires a commensurate effort in the understanding and modeling of the hadronic and nuclear physics of these interactions, which is incorporated as a nuclear model in neutrino event generators. This model is essential to every phase of experimental analyses and its theoretical uncertainties play an important role in interpreting every result. In this White Paper we discuss in detail the impact of neutrino-nucleus interactions, especially the nuclear effects, on the measurement of neutrino properties using the determination of oscillation parameters as a central example. After an Executive Summary and a concise Overview of the issues, we explain how the neutrino event generators work, what can be learned from electron-nucleus interactions and how each underlying physics process - from quasi-elastic to deep inelastic scattering - is understood today. We then emphasize how our understanding must improve to meet the demands of future experiments. With every topic we find that the challenges can be met only with the active support and collaboration among specialists in strong interactions and electroweak physics that include theorists and experimentalists from both the nuclear and high energy physics communities.

• The paper outlines the limitations of current neutrino-nucleus models and suggests improvements for accurate oscillation measurements.
• It highlights how nuclear effects, including nucleon correlations and final state interactions, complicate interaction predictions.
• The study emphasizes the need for precise cross-section measurements and better integration of models into event generators for reliable simulations.

Overview of NuSTEC White Paper: Status and Challenges of Neutrino-Nucleus Scattering

The NuSTEC White Paper provides a comprehensive examination of the current state and challenges in neutrino-nucleus scattering, a critical aspect for understanding neutrino interactions in particle physics experiments. This detailed inquiry is essential for the progress of numerous neutrino experiments worldwide, including those aiming to precisely measure neutrino oscillation parameters and cornerstone experiments like DUNE and T2HK.

Objectives and Scope

The principal focus of the paper is the intersection of neutrino physics with nuclear physics, which presents complex challenges due to the inherent uncertainties in modeling neutrino-nucleus interactions. Neutrino interactions are central to oscillation experiments, requiring a robust understanding of both strong and electroweak interactions. The paper particularly highlights the need for more accurate models that can predict interactions across a wide energy range, from quasi-elastic through deep inelastic scattering modes, and address the interplay between the incident neutrino and the complex nuclear environment.

Key Challenges

1. Modeling Neutrino-Nucleus Scattering:
   • Current models, such as the Relativistic Fermi Gas, are inadequate for high-precision experiments. Improvements in nuclear models are necessary to describe processes like quasi-elastic scattering, resonance production, and deep inelastic scattering consistently.
2. Incorporation of Nuclear Effects:
   • A significant portion of the white paper is dedicated to understanding the role of nuclear effects, such as nucleon-nucleon correlations and meson exchange currents, which could significantly alter the interaction cross-section and produce misleading results in neutrino oscillation studies.
3. Cross-Section Measurements:
   • Accurate theoretical predictions are limited by the lack of precise cross-section measurements for neutrino interactions on different nuclei, emphasizing the necessity for an increased focus on systematic experimental data collection, particularly in the transition and high-energy regions.
4. Final State Interactions (FSI):
   • The paper underscores the challenges in modeling FSIs where secondary interactions within the nucleus can affect the initial neutrino-nucleon interaction’s observable outcomes.
5. Implementation in Event Generators:
   • It highlights the critical role of Monte Carlo event generators in translating theoretical models into practical simulations, which need improvements to fully integrate recent theoretical advancements.

Implications and Future Directions

The research outlined in the white paper serves as the foundation for addressing systematic errors in neutrino oscillation experiments—errors that arise from deficiencies in interaction models. The recommendations stress not only advancements in theoretical modeling and experimental validation but also enhanced collaboration across nuclear and high-energy physics disciplines. There is a call for a coordinated international effort to foster a deeper integration of refined models into the experimental toolkit, particularly in enhancing neutrino event generators used across experiments.

Conclusion

The NuSTEC White Paper underscores the intricate challenges and the imperative need for new strategies in the study of neutrino-nucleus interactions. By identifying theoretical and experimental gaps, it seeks to inform future research directions that could lead to significant improvements in our understanding of neutrino physics, thereby refining the precision of neutrino experiments critical for exploring fundamental physics beyond the standard model.