Production of spectator neutrons, protons and light fragments on fixed targets at NICA

The Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model was connected to a set of models called Ablation Monte Carlo (AMC) to identify excited spectator fragments on completion of the UrQMD modeling of nucleus-nucleus collisions and then simulate spectator decays. The UrQMD-AMC approach combines the Minimum Spanning Tree (MST) clustering algorithm, which associates individual nucleons with excited clusters termed prefragments, with decay models of excited nuclei from the Geant4 toolkit. The relevant decay model for the prefragments decay is selected based on their mass and excitation energy, and includes nuclear evaporation, statistical multifragmentation and Fermi breakup models. The UrQMD-AMC approach was validated by comparing its results with data on the rapidity and transverse momentum distributions of neutrons and light fragments from 600A[Formula: see text]MeV [Formula: see text] and 10.6A[Formula: see text]GeV [Formula: see text] collisions. This approach supplements the evolution of individual nucleons during a nucleus–nucleus collision simulated with UrQMD with nucleon clustering to simulate also the production of spectator nuclear fragments, which are not produced in the UrQMD model alone.