Intermediate Heavy Ion Collisions Research Articles

Production of magnetic field due to heavy ion collisions around transition energy

Isospin quantum molecular dynamics (IQMD) model is a reliable computational tool for the study of various phenomena (multi fragmentation, anisotropic flow, nuclear stopping) from low to intermediate heavy ion collisions (HICs). Here, simulation has been carried out for the magnetic field generated during non-central HICs using the IQMD model. The effect of various parameters, such as centrality, angular momentum, rapidity and incident energy has been thoroughly investigated on the magnetic field with the evolution of time and space. It has been observed that the rapidity bin significantly impacts the magnitude of the magnetic field in different directions. Furthermore, the magnetic field produced during HIC leads to a notable impact on the in-plane momentum of the proton and neutron.

Extending the dynamic range of electronics in a Time Projection Chamber

Abstract When Time Projection Chambers (TPCs) are used in low to intermediate heavy ion collisions, the mass and momentum range of the emitted particles cover a wide range in energy losses. Many TPC readout electronics currently only have a single gain output with a fixed dynamic range. In a recent set of experiments using the SAMURAI Pion-Reconstruction and Ion-Tracker (S π RIT) TPC, it was important to simultaneously measure relativistic pions and heavy ion tracks from the same collisions. As the ionization from a track’s energy loss is collected and multiplied by the anode wires, a distribution of image charges is induced on the TPC read-out pads. If the avalanche on a wire is large enough, the charge collected by pads directly underneath will saturate the readout electronics; pads farther away in the distribution will not be saturated. Using these unsaturated pads and the known pad distribution function, we can estimate the charge on saturated pads, increasing the dynamic range by a factor of 5.

Symmetry energy and experimentally observed cold fragments in intermediate heavy-ion collisions**Supported by National Natural Science Foundation of China (U1432247, 11605097), National Basic Research Program of China (973 Program, 2014CB845405), Doctoral Scientific Research Foundation of Inner Mongolia University for the Nationalities (BS365)

An attempt is made to study the symmetry energy at the time of primary fragment formation from the experimentally observed cold fragments for a neutron-rich system of 64Ni + 9Be at 140 MeV/nucleon, utilizing the recent finding that the excitation energy becomes lower for more neutron-rich isotopes with a given Z value. The extracted asym/T values from the cold fragments, based on the Modified Fisher Model (MFM), are compared to those from the primary fragments of the antisymmetrized molecular dynamics (AMD) simulation and become consistent with the simulation when the I = N − Z value becomes larger, indicating that the excitation energy of these neutron-rich isotopes is indeed lower.

Shape analysis applied in heavy ion reactions near Fermi energy

A new method is proposed to perform shape analyses and to evaluate their validity in heavy ion collisions near the Fermi energy. In order to avoid erroneous values of shape parameters in the calculation, a test particle method is utilized in which each nucleon is represented by n test particles, similar to that used in the Boltzmann–Uehling–Uhlenbeck (BUU) calculations. The method is applied to the events simulated by an antisymmetrized molecular dynamics model. The geometrical shape of fragments is reasonably extracted when n = 100 is used. A significant deformation is observed for all fragments created in the multifragmentation process. The method is also applied to the shape of the momentum distribution for event classification. In the momentum case, the errors in the eigenvalue calculation become much smaller than those of the geometrical shape analysis and the results become similar between those with and without the test particle method, indicating that in intermediate heavy ion collisions the shape analysis of momentum distribution can be used for the event classification without the test particle method.

Novel determination of density, temperature, and symmetry energy for nuclear multifragmentation through primary fragment-yield reconstruction

For the first time primary hot isotope distributions are experimentally reconstructed in intermediate heavy ion collisions and used with antisymmetrized molecular dynamics (AMD) calculations to determine density, temperature and symmetry energy coefficient in a self-consistent manner. A kinematical focusing method is employed to reconstruct the primary hot fragment yield distributions for multifragmentation events observed in the reaction system $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon. The reconstructed yield distributions are in good agreement with the primary isotope distributions of AMD simulations. The experimentally extracted values of the symmetry energy coefficient relative to the temperature, $a_{sym}/T$, are compared with those of the AMD simulations with different density dependence of the symmetry energy term. The calculated $a_{sym}/T$ values changes according to the different interactions. By comparison of the experimental values of $a_{sym}/T$ with those of calculations, the density of the source at fragment formation was determined to be $\rho /\rho_{0} = (0.63 \pm 0.03 )$. Using this density, the symmetry energy coefficient and the temperature are determined in a self-consistent manner as $a_{sym} = (24.7 \pm 1.9) MeV$ and $T=(4.9 \pm 0.2)$ MeV

Can quark effects be observed in intermediate heavy ion collisions?

In recent years a tentative description of the short-range part of hadron interactions with constituent quark interchange has been developed providing an alternative approach to meson physics. Quark interchange plays a role, for example, in the nucleon–nucleon (NN) phase shifts and cross-section. In heavy ion collision simulations at intermediate energies one of the main features is the NN cross-section in the collisional term, where in most cases it is an input adjusted to the free space value. In this paper we introduce the quark degrees of freedom to the NN cross-section in the Vlasov–Uehling–Uhlenbeck (VUU) model and explore the possibility that these effects appear in the observables at lower energies.

Nuclear stopping as a probe for in-medium nucleon-nucleon cross sections in intermediate energy heavy ion collisions.

Using an isospin-dependent quantum molecular dynamics, nuclear stopping in intermediate heavy ion collisions has been studied. The calculation has been done for colliding systems with different neutron-proton ratios in beam energy ranging from 15 MeV/ u to 150 MeV/ u. It is found that, in the energy region from above Fermi energy to 150 MeV/ u, nuclear stopping is very sensitive to the isospin dependence of in-medium nucleon-nucleon cross section, but insensitive to symmetry potential. From this investigation, we propose that nuclear stopping can be used as a new probe to extract the information on the isospin dependence of in-medium nucleon-nucleon cross section in intermediate energy heavy ion collisions.

An analytic solution for energy loss and time-of-flight calculations for intermediate-energy light ions

Particle identification in intermediate heavy-ion collisions, using a modern 4π detector which contains several active layers, relies on a parametrisation or numerical integration of the energy loss in thick layers of detector material for different ions. Here an analytical solution applicable over an energy range of a few MeV up to a 100 A MeV and for ions up to at least Z=8 is presented. Also, the consequences for time-of-flight measurements (TOF) in detectors behind several thick layers of detector material are discussed. The solution is applied to the data of the Huygens detector, which uses a TPC (d E/d x) and plastic scintillators for particle identification ( E and TOF or d E/d x and TOF).