Coupled Channels Reduced Order Scattering Emulators

Reaction theory requires calibration and uncertainty quantification (UQ) of the effective potential parameters, which is often achieved using Bayesian methods. Recent UQ studies involve constraining the two-body interaction with elastic scattering and then propagating the parametric uncertainty to the reaction channel of interest using only the simplest theories due to computational feasibility [1]. It is important to go beyond such simple reaction models to extract physical information from modern experimental measurements (such as the ones performed at the Facility for Rare Isotope Beams). However, state-of-the-art reaction methods (such as the Continuum Discretized Coupled Channels method) can take hours for a single calculation. Bayesian methods often require thousands or millions of calculations to correctly sample the model’s parameter space. Recent physics-informed emulators using Reduced Basis Methods (RBMs) such as the Reduced Order Scattering Emulator (ROSE) [2] have shown significant time advantage for elastic scattering calculations. Here we expand this method to fast and accurately execute general coupled channels scattering calculations, therefore opening a gateway to perform Bayesian studies of more complex nuclear reactions. As a demonstration, we implement our method for realistic nucleon-target inelastic scattering using a collective excitation model. We then perform Bayesian calibrations for varying projectile-target systems with controlled trade-offs between emulator speed and accuracy. 

[1] A. E. Lovell, F. M. Nunes, M. Catacora-Rios, and G. B. King, J. Phys. G 48, 014001 (2020), 2012.09012 

[2] D. Odell, P. Giuliani, K. Beyer, M. Catacora-Rios, M. Y.-H. Chan, E. Bonilla, R. J. Furnstahl, K. Godbey, and F. M. Nunes, PhysRevC.109.044612 (2024),