Coherent pion production in neutrino-nucleus scattering within multiple-scattering formalism

• Applicant: Dr. Viacheslav Tsaran
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 572608475

Pion production plays a significant role in the measured signals for both inclusive and semi-inclusive neutrino-nucleus scattering cross sections, presenting a considerable challenge to achieving an accurate theoretical description needed to interpret the long-baseline neutrino oscillation experiments. To address this issue, we first aim to extend the unified model for nuclear pion scattering and photoproduction in the Δ-resonance energy region, developed in previous works. Our approach is based on the distorted wave impulse approximation in momentum space, extended for a detailed description of second-order pion rescattering. The nuclear potentials for both pion scattering and production are derived from the multiple-scattering series and incorporate intermediate pion-nucleon charge exchange and nucleon spin-flip processes. The many-body medium effects are incorporated in the complex effective Δ self-energy, modifying the Δ-propagator in the nuclear medium. Pions produced in the neutrino-nucleus scattering process undergo significant final-state interaction, which can lead to changes in their charge or their complete absorption. To describe these effects more accurately, this proposal aims to extend our calculations of pion-nucleus scattering, including pion-nucleus charge exchange and true pion absorption processes. To cover the energy range relevant to modern long-baseline neutrino oscillation experiments, we plan to expand our model to the second nucleon resonance energy region. This will involve incorporating the modifications to the mass and width of the N(1440), N(1520), and N(1535) resonances within the nuclear medium. Incorporating the hadronic axial-vector current into the elementary pion production amplitude, we aim to develop a comprehensive model for pion production in neutrino-nucleus scattering. This model will account for second-order pion rescattering effects, which were found to play a significant role in nuclear pion photoproduction. This project aims to establish a unified framework for describing pion scattering and electroweak production within the first and second nucleon-resonance energy regions, using nuclear structure input from modern nuclear theory and relying on a minimal set of model parameters.

• DFG Programme: Research Grants