Intermediate Energy Heavy Ion Collisions Research Articles

Hot and dense QCD shear viscosity at (almost) NLO

The next-to-leading order weak-coupling shear viscosity of QCD was computed 6 years ago. However, these results have never been applied at finite baryon chemical potential μ, even though intermediate-energy heavy ion collisions and merging neutron stars may explore the Quark-Gluon Plasma in a regime where baryon chemical potentials are large. Here, we extend the next-to-leading order shear viscosity calculations to finite μ, and we show that, while the convergence of the weak-coupling expansion is questionable for achievable plasmas, it is somewhat better at μ > T than at μ = 0.

Estimation of electric field in intermediate-energy heavy-ion collisions

We estimate the spacetime profile of the electric field in head-on heavy-ion collisions at intermediate collision energies sNN=O(3–10GeV). Using a hadronic cascade model (JAM; Jet AA Microscopic transport model), we numerically demonstrate that the produced field has strength eE=O((30–60MeV)2), which is supercritical to the Schwinger limit of QED and is non-negligibly large compared even to the hadron/QCD scale, and survives for a long time τ=O(10fm/c) due to the baryon stopping. We show that the produced field is nonperturbatively strong in the sense that the nonperturbativity parameters (e.g., the Keldysh parameter) are sufficiently large. This is in contrast to high-energy collisions sNN≳100GeV, where the field is extremely short-lived and hence is perturbative. Our results imply that the electromagnetic field may have phenomenological impacts on hadronic/QCD processes in intermediate-energy heavy-ion collisions and that heavy-ion collisions can be used as a new tool to explore strong-field physics in the nonperturbative regime. Published by the American Physical Society 2024

Isospin Correlations in Isotope Yields at Intermediate and High Energy Heavy-Ion Collisions

Isospin Correlations in Isotope Yields at Intermediate and High Energy Heavy-Ion Collisions

Quasi-monoenergetic heavy ion acceleration driven by sub-100 PW linearly polarized laser pulses in the radiation-dominated QED regime

Heavy ion acceleration from an ultrathin foil target irradiated by a p-polarized and spatially Gaussian laser pulse at intensity of 1023 W/cm2 is studied by using two-dimensional particle-in-cell simulations. We find that, in the extremely intense laser fields, the radiation reaction force from bright γ-rays radiated by radially oscillating electrons is large enough to match the Coulomb explosive force of foil electrons. The undesirable transverse expansion of the foil from the electron heating and inhomogeneous radial profile of the laser intensity is effectively suppressed. The foil maintains relatively good opacity in its central region stabilizing localized acceleration of heavy ions. With a laser of intensity 3.4 × 1023 W/cm2, duration of 33 fs, and power of 96 PW, a dense monoenergetic Au79+ ion bunch with a peak energy of ∼160 GeV can be obtained in the radiation-dominated QED regime. Such a high-quality heavy ion beam is useful for investigating nuclear matter equation of state and quantum chromodynamic phase transition in intermediate-energy heavy ion collisions.

Spin dynamics in intermediate-energy heavy-ion collisions with rigorous angular momentum conservation

Spin dynamics in intermediate-energy heavy-ion collisions with rigorous angular momentum conservation

Properties of collective flow and pion production in intermediate-energy heavy-ion collisions with a relativistic quantum molecular dynamics model

Properties of collective flow and pion production in intermediate-energy heavy-ion collisions with a relativistic quantum molecular dynamics model

Transport model comparisons for intermediate-energy heavy-ion collisions

Transport model comparisons under controlled conditions are performed in order to evaluate the robustness of their predictions in heavy-ion collisions (HICs). Including many of the currently used transport codes comparisons are done in periodic boxes and for typical HICs at intermediate energies in the hadronc regime. In this way we succeed to understand the different results between codes and evaluate different simulation strategies. Ways to arrive at an uncertainty quantification of transport model studies are discussed.

Search for toroids in excited nuclear material

Ground state nuclei usually have compact geometries. However, there have been theoretical predictions that excited nuclei can take on more extended shapes such as toroids or bubbles. There have been many attempts to identify signatures of such shapes in experimental data. One signature, both predicted by theory and reported in experimental data, is narrow resonances at high excitation energy in peripheral intermediate-energy heavy-ion collisions. This potential evidence for toroidal states was reported in the alpha particle disassembly of 28Si after collision with a 12C target at 35 MeV/nucleon. The prior work was limited by angular resolution and statistical uncertainties. The present work aims to measure the excitation energy distribution for these disassembly events with improved angular resolution and reduced statistical uncertainty using the Forward Array Using Silicon Technology (FAUST). FAUST is equipped with resistive dual-axis duo-lateral (DADL) position-sensitive silicon detectors capable of sub-millimeter position resolution. The measured excitation energy distributions of 7-α disassembly events showed no strong evidence for highly excited states at the cross section and widths suggested by previous experiment.

Kinetic approach of light-nuclei production in intermediate-energy heavy-ion collisions

Kinetic approach of light-nuclei production in intermediate-energy heavy-ion collisions

Impact of quadrupole deformation on intermediate-energy heavy-ion collisions

Impact of quadrupole deformation on intermediate-energy heavy-ion collisions

Influence of Fragment Size on Isospin Effects in Transverse and Elliptic Flows and Nuclear Stopping in Intermediate Energy Heavy-Ion Collision

Influence of Fragment Size on Isospin Effects in Transverse and Elliptic Flows and Nuclear Stopping in Intermediate Energy Heavy-Ion Collision

In-medium effect and collective flow of pion production in intermediate energy heavy-ion collisions

In-medium effect and collective flow of pion production in intermediate energy heavy-ion collisions

Hot and dense QCD shear viscosity at leading log

The leading-order weak-coupling shear viscosity of QCD was computed almost 20 years ago, and the extension to next-to-leading order is 4 years old. But these results have never been applied at finite baryon chemical potential μ, despite the fact that intermediate-energy heavy ion collisions and merging neutron stars may explore the Quark-Gluon Plasma in a regime where baryon chemical potentials are large. Here we extend the leading-log shear viscosity calculation to finite μ, and we argue that the convergence of the weak-coupling expansion, while questionable for achievable plasmas, should be better at μ > T than at μ = 0.

Revisiting Angular Momentum Conservation in Transport Simulations of Intermediate-Energy Heavy-Ion Collisions

Based on the well-calibrated IBUU transport model, we have studied the dynamical effect of incorporating rigorous angular momentum conservation in each collision of particles with homework setups. The constraint of the rigorous angular momentum conservation requires in-plane collisions and side jumps of particles after their collision. Since the option is not unique, we have compared two typical prescriptions with the original one. While the results depend quantitatively on the choice of the prescription, we found that the angular momentum conservation generally reduces local density fluctuations and thus the collision rate and may have some influence on the density evolution, the collective flow, and even the pion production in transport simulations of intermediate-energy heavy-ion collisions.

Nonequilibrium Hydrodynamic Approach to Describing the Emission of High-Energy Secondary Particles in Intermediate-Energy Heavy-Ion Collisions

Nonequilibrium Hydrodynamic Approach to Describing the Emission of High-Energy Secondary Particles in Intermediate-Energy Heavy-Ion Collisions

Isospin effects on intermediate mass fragments at intermediate energy-heavy ion collisions

Isospin effects on intermediate mass fragments at intermediate energy-heavy ion collisions

Density fluctuations in intermediate-energy heavy-ion collisions

Density fluctuations in intermediate-energy heavy-ion collisions

Model independent reconstruction of impact parameter distributions for intermediate energy heavy ion collisions

We present a model independent method to reconstruct the impact parameter distributions of experimental data for intermediate energy heavy ion collisions, adapted from a recently proposed approach for ultra-relativistic heavy ion collisions. The method takes into account the fluctuations which are inherent to the relationship between any experimental observable and the impact parameter in this energy range. We apply the method to the very large dataset on heavy ion collisions in the energy range 20--100 MeV/nucleon obtained with the INDRA multidetector since 1993, for two observables which are the most commonly used for the estimation of impact parameters in this energy range. The mean impact parameters deduced with this new method for ``central'' collisions selected using typical observable cuts are shown to be significantly larger than those found when fluctuations are neglected, and as expected the difference increases as bombarding energy decreases. In addition, we will show that this new approach may provide previously inaccessible experimental constraints for transport models, such as an estimation of the extrapolated mean value of experimental observables for $b=0$ collisions. The ability to give more realistic, model independent estimations of the impact parameters associated with different experimental datasets should improve the pertinence of comparisons with transport model calculations which are essential to better constrain the equation of state of nuclear matter.

Influence of Model Assumptions on Radial Flow Investigations in Heavy-Ion Collisions

An effective way for the investigation of nuclear matter under the extreme conditions of high density and temperature is the study of nuclear fragmentation, realized in intermediate-energy heavy-ion collisions. The potential energy accumulated in the compression zone of the collision is converted into collective flow of matter in the later stages of the reaction. During the expansion of the system, fragments are formed in a clusterization process. In the final stage of the reaction, the fragments are moving along Coulomb trajectories and may deexcite by particle emission or secondary break-up.In order to verify the influence of the collective energy on the experimental energy spectra and extract quantitative information on the thermal and collective components, a model simulation was developed. In this procedure, the evolution of the disintegrating system in a multifragmentation process was described after the freeze-out stage with a Monte-Carlo approach. A reconstruction procedure for the fragment kinetic energies has shown the possibility to obtain the thermal and collective components from measured fragment spectra. In the present work, we scrutinize the model simulation for the evolution of the disintegrating system by testing the sensitivity of the collective expansion energy extraction on the model assumptions concerning the freeze-out characteristics, such as the size and shape of the freeze-out volume. Furthermore, thermal aspects of the early stage of the expansion are tested with an examination of the relationship between the assumption of the degree of thermalization of the emitting source and the extracted value of the collective energy.

Effects of cluster correlations on fragment emission in C12+C12 at 50 MeV/nucleon

The effects of cluster correlations have been studied in the $^{12}\mathrm{C}+^{12}\mathrm{C}$ reaction at 50 MeV/nucleon, using three antisymmetrized molecular dynamics (AMD) models, the AMD (AMD/D) without any additional cluster correlations, AMD/D-COALS with nucleon correlations based on a coalescence prescription for light cluster formations with $A\ensuremath{\le}4$, and AMD-cluster with an extended cluster correlation in two-nucleon collision processes and a special treatment for intermediate fragment formation with $A\ensuremath{\le}9$. The angular distributions and energy spectra of fragments have been simulated and compared with the available experimental data. It is found that the cluster correlations take a crucial role to describe the productions of light charged particles (LCPs) and intermediate mass fragments (IMFs), and the AMD-cluster studied here provides a consistent overall reproduction of the experimental data. It is also shown that the significant effects of the secondary decay processes are involved for the fragment production besides the dynamical productions in the AMD stage. Detailed LCP and IMF production mechanisms involved in the intermediate energy heavy ion collisions are discussed.