Speaker
Description
Single pion production (SPP) is an important interaction mechanism in accelerator-based neutrino experiments, contributing significantly to total cross-sections and impacting precision measurements. Its study is essential for understanding neutrino oscillations, distinguishing signal from background, and refining theoretical models, which will help to reduce systematic errors in the neutrino energy reconstruction [1].
Therefore, a realistic SPP model that covers the whole energy range in neutrino experiments and accounts for final state interactions (FSI) is crucial. The current operator within the Hybrid model consists of several Feynmann diagrams including four nucleon resonances ($P_{33}$, $D_{33}$, $P_{11}$ and $S_{11}$) and background terms from Chiral Perturbation Theory (ChPT) and an extension to the high energy region performed via Regge phenomenology [2]. This model is embedded in a sophisticated nuclear framework: the bound state is described as a Dirac solution within relativistic mean field (RMF) potentials. The final nucleon is in the relativistic distorted wave impulse approximation (RDWIA), a Dirac continuum state computed with energy dependent RMF potentials (EDRMF), so orthogonality between nucleon initial and final states is naturally implemented [3,4].
In recent work [5], we addressed the effect that the asymptotic approximation in the current operator has on inclusive and semi-inclusive cross sections. This is a step forward into a more complete and consistent treatment of SPP on the nucleus.
In a next step we implement FSI for the final pion, i.e., we describe the pion wave function with a RDWIA formalism. The pion continuum states are hence computed as solutions of the Klein-Gordon equation with a suitable nucleus-pion potential. The treatment of the final hadron wave functions, with distortion effects from the residual nucleus, is the only way of taking into account elastic FSI within a consistent, fully relativistic and quantum-mechanical framework.
In this contribution we will present our latest results from Ref. [5] and new updates towards the inclusion of the pion distortion within our model.
[1] L. Alvarez-Ruso et al., Prog. Part. Nuc. Phys. 100 (2018)
[2] R. González-Jiménez et al., Phys. Rev. D 95, 113007 (2017)
[3] R. González-Jiménez et al., Phys. Rev. C 100, 045501 (2019)
[4] A. Nikolakopoulos et al., Phys. Rev. D 107, 053007 (2023)
[5] J. García-Marcos et al., Phys. Rev. C 109, 024608 (2024)