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

Abstract

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 MeV Sn + Sn and 10.6A GeV Au + Ag 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.

Figures (5)

• Figure 1: Production of fragments with $Z \geq 3$ in the interactions of $10.6A$ GeV $^{197}$Au with Ag nuclei of nuclear emulsion calculated with UrQMD-AMC in the cascade mode (red dashed-line histograms) and with the Skyrme forces (blue solid-line histograms). Left panel: the average multiplicity of $Z \geq 3$ fragments as a function of the total charge bound in fragments $Z_{\rm bound}$ (see text for details), the black squares represent the experimental data by the EMU01 Collaboration Adamovich1999. Right panel: the transverse momentum distribution of $Z\geq 3$ fragments, the triangles represent the data by P. Jain et al.Jain1995.
• Figure 2: Production of helium ($Z=2$) fragments in the interactions of $10.6A$ GeV $^{197}$Au with Ag nuclei of nuclear emulsion calculated with UrQMD-AMC in the cascade mode (red dashed-line histograms) and with Skyrme forces (blue solid-line histograms). Left panel: the average multiplicity of $Z=2$ fragments as a function of the total charge bound in fragments $Z_{\rm bound}$ (see text for details), the black squares represent the experimental data by the EMU01 Collaboration Adamovich1999. Right panel: the transverse momentum distributions of $Z=2$ fragments. The black triangles represent the experimental data by the KLMM Jain1995 collaboration.
• Figure 3: Average multiplicity of neutrons as a function of $Z_{\rm bound}$ with its standard deviation represented by error bars calculated for collisions of $600A$ MeV $^{124}$Sn with $^{124}$Sn (left panel). The rapidity distribution of neutrons in the rest frame of the emitting nucleus calculated for the same collision system (right panel). The circles represent measurements Pawlowski2023, other notations are the same as in Fig \ref{['fig:frags']}.
• Figure 4: Calculated pseudorapidity distributions of neutrons (left) and protons (right) from collisions of $3.8A$ GeV $^{124}$Xe with a $^{130}$Xe target in the BM@N experiment (top), and with a $^{184}$W target in the MPD experiment (bottom). Dotted vertical lines mark the upper boundary of the pseudorapidity interval covered by forward calorimeters in the experiments.
• Figure 5: Same as in Fig. \ref{['fig:n_p_eta']}, but for deuterons (left) and $\alpha$-particles (right).