Emission In Heavy-ion Collisions Research Articles

Study and Investigation of Hard Photons Emission in Heavy Ion Collisions

This work involves hard photon rate production from quark -gluon plasma QGP interaction in heavy ion collision. Using a quantum chromodynamic model to investigate and calculation of photons rate in 𝑐𝑔 → 𝑠𝑔𝛾 system due to strength coupling, photons rate, temperature of system, flavor number and critical. The photons rate production computed using the perturbative strength models for QGP interactions. The strength coupling was function of temperature of system, flavor number and critical temperature. Its influenced by force with temperature of system, its increased with decreased the temperature and vice versa. The strength coupling has used to examine the confinement and deconfinement of quarks in QGP properties and influence on the photon rate production. In our approach, we calculate the photons rate depending on the strength coupling, photons rate and temperature of system with other factors. The results plotted as a function of the photons energy. The photons rate was decreased with increased temperature and increased with decreased with strength coupling.

\({\mit \Lambda }(1520)\) and \(\phi \) as Potential Sources of \(K^{-}\) Meson Emission in Heavy-ion Collisions Around Kaon Threshold

\({\mit \Lambda }(1520)\) and \(\phi \) as Potential Sources of \(K^{-}\) Meson Emission in Heavy-ion Collisions Around Kaon Threshold

Contribution of next-to-leading order and Landau-Pomeranchuk-Migdal corrections to thermal dilepton emission in heavy-ion collisions

Recently lots of efforts have been made to obtain the next to leading order and Landau-Pomeranchuk-Migdal corrections to the thermal dilepton emission rate in perturbative QCD. Here we apply these results to the plasma created in heavy ion collisions and see wether these corrections improve the comparison between theoretical calculations and experimental results for the invariant mass dependence of the dilepton emission rate. In particular, we simulate the quark-gluon plasma produced at RHIC and LHC using a 2+1-dimensional viscous hydro model. We compare our results to STAR experiment and comment on the need for a non-perturbative determination of the dilepton rate at low invariant mass.

Correlation between the fragmentation modes and light charged particles emission in heavy ion collisions

The correlation between the shape of rapidity distribution of the yield of light charged particles and the fragmentation modes in semi-peripheral collisions for 70Zn+70Zn, 64Zn+64Zn and 64Ni+64Ni at the beam energy of 35 MeV/nucleon is investigated based on ImQMD05 code. Our studies show there is an interplay between the binary, ternary and multi-fragmentation break-up modes. The binary and ternary break-up modes more prefer to emit light charged particles at middle rapidity and give larger values of R yield mid compared with the multi-fragmentation break-up mode does. The reduced rapidity distribution for the normalized yields of p, d, t, 3He, 4He and 6He and the corresponding values of R yield mid can be used to estimate the probability of multi-fragmentation break-up modes. By comparing to experimental data, our results illustrate that ≥40% of the collisions events belong to the multifragmentation break-up mode for the reactions we studied.

Pre-equilibrium α-particle emission as a probe to study α-clustering in nuclei

A theoretical approach was developed to describe secondary particle emission in heavy ion collisions, with special regards to pre-equilibrium {\alpha}-particle production. Griffin's model of non-equilibrium processes is used to account for the first stage of the compound system formation, while a Monte Carlo statistical approach was used to describe the further decay from a hot source at thermal equilibrium. The probabilities of neutron, proton and {\alpha}-particle emission have been evaluated for both the equilibrium and pre-equilibrium stages of the process. Fission and {\gamma}-ray emission competition were also considered after equilibration. Effects due the possible cluster structure of the projectile which has been excited during the collisions have been experimentally evidenced studying the double differential cross sections of p and {\alpha}-particles emitted in the E=250MeV 16O +116Sn reaction. Calculations within the present model with different clusterization probabilities have been compared to the experimental data.

Effective mass splitting of neutron and proton and isospin emission in heavy-ion collisions

Within the framework of an isospin and momentum dependent transport model, the emissions of isospin particles (nucleons and light clusters) squeezed out in heavy-ion collisions are investigated as probes of the poorly known symmetry energy at high baryon density. Two different mass splittings of neutrons and protons in nuclear medium as mn⁎>mp⁎ and mn⁎<mp⁎ are used in the model and their influence on the isospin emission in heavy-ion collisions is discussed thoroughly. The competition between the stiffness and the momentum dependence of the symmetry potential on reaction dynamics are compared and systematically analyzed. It is found that the difference of the neutron and proton directed flows and the transverse momentum distribution of the neutron/proton ratio are sensitive to the stiffness of the symmetry energy, which cannot be changed with the controversial effective mass splitting. The elliptic flows of free nucleons at high transverse momentum within mid-rapidity emission are to be promising observables as distinguishing the nucleon effective mass splitting.

Elliptic flow studies in heavy-ion collisions using the CMS detector

The azimuthal anisotropy of charged particle emission in heavy ion collisions is a sensitive probe of the properties and the dynamical evolution of the produced matter. The systematic study of elliptic flow (v2), and higher order harmonics can yield information about the equilibration timescale, the nuclear equation of state and the viscosity in the different stages of the system evolution, as well as the initial state conditions of the heavy ion collisions. Experimentally, it is important to be able to reconstruct the flow using different methods, since they have different sensitivity to non-flow correlations and fluctuations which affect the extracted signal. In CMS, the nuclear reaction plane can be determined independently using several different detector subsystems. The reconstruction of elliptic flow using calorimetry and the tracking system is presented.

Dynamics of pion production in heavy-ion collisions around1A GeV energies

Within the framework of the improved isospin-dependent quantum molecular dynamics model, the dynamics of pion emission in heavy-ion collisions in the region of $1$$A$ GeV energies as a probe of nuclear symmetry energy at suprasaturation densities is investigated systematically. The total pion multiplicities and the ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ yields are calculated for selected Skyrme parameters SkP, SLy6, Ska, and SIII and also for the cases of different stiffness of symmetry energy with the parameter SLy6. The influence of Coulomb potential, symmetry energy, and in-medium pion potential on the pion production is investigated and compared to each other by analyzing the distributions of transverse momentum and longitudinal rapidity and also the excitation functions of the total pion and the ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ ratio. The directed flow, elliptic flow, and polar-angle distributions are calculated for the cases of different collision centralities and also the various stiffnesses of the symmetry energies. A comparison of the calculations with the available experimental data is performed.

Calculations of direct photon emission in heavy ion collisions at = 200 GeV

Direct photon emission in heavy-ion collisions is calculated within a relativistic micro+macro hybrid model and compared to the microscopic transport model UrQMD. In the hybrid approach, the high-density part of the collision is calculated by an ideal 3+1-dimensional hydrodynamic calculation, while the early (pre-equilibrium-) and late (rescattering-) phase are calculated with the transport model. We study both models with Au + Au-collisions at = 200 GeV and compare the results to experimental data published by the PHENIX collaboration.

Hybrid model calculations of direct photons in high-energy nuclear collisions

Direct photon emission in heavy-ion collisions is calculated within a relativistic micro $+$ macro hybrid model and compared to the microscopic transport model, the Ultra-relativistic Quantum Molecular Dynamics model. In the hybrid approach, the high-density part of the evolution is replaced by an ideal three-dimensional hydrodynamic calculation. This allows the effects of viscosity and full local thermalization, in comparison with the transport model of the ideal fluid dynamics, to be examined. The origin of high-${p}_{\ensuremath{\perp}}$ photons as well as the impact of elementary high-$\sqrt{s}$ collisions is studied. The contribution of different production channels and nonthermal radiation to the spectrum of direct photons is further explored. Detailed comparisons to the measurements by the WA98 Collaboration are also undertaken.

Dynamical dipoleγradiation in heavy-ion collisions on the basis of a quantum molecular dynamics model

Dynamical dipole $\ensuremath{\gamma}$-ray emission in heavy-ion collisions is explored in the framework of the quantum molecular dynamics model. The studies are focused on systems of $^{40}\mathrm{Ca}$ bombarding $^{48}\mathrm{Ca}$ and its isotopes at different incident energies and impact parameters. Yields of $\ensuremath{\gamma}$ rays are calculated and the centroid energy and dynamical dipole emission width of the $\ensuremath{\gamma}$ spectra are extracted to investigate the properties of $\ensuremath{\gamma}$ emission. In addition, sensitivities of dynamical dipole $\ensuremath{\gamma}$-ray emission to the isospin and the symmetry energy coefficient of the equation of state are studied. The results show that detailed study of dynamical dipole $\ensuremath{\gamma}$ radiation can provide information on the equation of state and the symmetry energy around the normal nuclear density.

Probing high-density behavior of symmetry energy from pion emission in heavy-ion collisions

Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, the emission of pion in heavy-ion collisions in the region 1 A GeV as a probe of nuclear symmetry energy at supra-saturation densities is investigated systematically, in which the pion is considered to be mainly produced by the decay of resonances Δ(1232) and N∗(1440). The total pion multiplicities and the π−/π+ yields are calculated for selected Skyrme parameters SkP, SLy6, Ska and SIII, and also for the cases of different stiffness of symmetry energy with the parameter SLy6. Preliminary results compared with the measured data by the FOPI Collaboration favor a hard symmetry energy of the potential term proportional to (ρ/ρ0)γs with γs=2.

Pion Production in Heavy-Ion Collisions in the 1 A GeV Region

Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, pion emission in heavy-ion collisions in the region 1 A GeV is investigated systematically, in which the pion is considered to be mainly produced by the decay of resonances Δ(1232) and N* (1440). The in-medium dependence and Coulomb effects of pion production are included in the calculation. Total pion multiplicity and π−/π+ yields are calculated for the reaction 197Au+197Au in central collisions for selected Skyrme parameters SkP, SLy6, Ska, SIII and compared with the measured data of the FOPI collaboration.

Direct photon emission from hadronic sources: hydrodynamics vs. transport theory

Direct photon emission in heavy-ion collisions is calculated within the relativistic microscopic transport model UrQMD. We compare the results from the pure transport calculation to a hybrid-model calculation, where the high-density part of the evolution is replaced by an ideal 3-dimensional fluid-dynamic calculation. The effects of viscosity, present in the transport model but neglected in ideal fluid dynamics, are examined. We study the contribution of different production channels and non-thermal collisions to the spectrum of direct photons. Detailed comparisons to the measurements by the WA 98 collaboration are undertaken.

Conical emission in heavy-ion collisions

A broadened or double humped away-side structure was observed in 2-particle azimuthal jet-like correlations at RHIC and SPS. This modification can be explained by conical emission, from either Mach-cone shock waves or Čerenkov gluon radiation, and by other physics mechanisms, such as large angle gluon radiation, jets deflected by radial flow and path-length-dependent energy loss. Three-particle jet-like correlations are studied for their power to distinguish conical emission from other mechanisms. This paper discusses Mach-cone shock waves, Čerenkov gluon radiation and the experimental evidence for conical emission from RHIC and SPS.

Hydrokinetic model of the matter evolution in A + A collisions at RHIC and LHC energies

Using the hydrokinetic model of pionic emission in heavy ion collisions, we study the effects of continuous particle emission for 3D azimuthal symmetric Bjorken-type expansion. We describe RHIC pion data in central A + A collisions and make predictions for LHC based on the hydrokinetic model and initial conditions taken from the color glass condensate model.

Effect of entrance-channel asymmetry on the isospin dependence of nucleon emission in heavy ion collisions**Supported by National Natural Science Foundation of China (10575119, 10775061), Knowledge Innovation Project of Chinese Academy of Sciences (KJCX3-SYW-N2), Major State Basic Research Developing Program of China (2007CB815004), CAS/SAFEA International Partnership Program for Creative Research Teams (CXTD-J2005-1), and the Asia-Link Project of the European Commission (CN/ASIA-LINK/008(94791))

Using the isospin- and momentum-dependent hadronic transport model IBUU04, we have investigated the influence of the entrance-channel isospin asymmetry on the sensitivity of the pre-equilibrium neutron/proton ratio to symmetry energy in central heavy-ion collisions induced by high-energy radioactive beams. Our analysis and discussion are based on the dynamical simulations of the three isotopic reaction systems 132Sn+124Sn, 124Sn+112Sn and 112Sn+112Sn which are of the same total proton number but different isospin asymmetry. We find that the kinetic-energy distributions of the pre-equilibrium neutron/proton ratio are quite sensitive to the density-dependence of symmetry energy at incident beam energy E/A = 400 MeV, and the sensitivity increases as the isospin asymmetry of the reaction system increases.

Systematics of pion emission in heavy ion collisions in the [formula omitted] regime

Using the large acceptance apparatus FOPI, we study pion emission in the reactions (energies in A GeV are given in parentheses): 40Ca + 40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 96Ru + 96Ru (0.4, 1.0, 1.5), 96Zr + 96Zr (0.4, 1.0, 1.5), 197Au + 197Au (0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include longitudinal and transverse rapidity distributions and stopping, polar anisotropies, pion multiplicities, transverse momentum spectra, ratios ( π + / π − ) of average transverse momenta and of yields, directed flow, elliptic flow. The data are compared to earlier data where possible and to transport model simulations.

Nonperturbative finiteTbroadening of the ρ meson and dilepton emission in heavy-ion collisions

We study self-consistently the finite T broadening of the {rho} meson and its implications for dilepton emission in heavy-ion collisions. For this purpose finite width effects at finite temperature due to the {rho}-{pi} interaction are investigated in a self-consistent {phi}-functional approach. The temperature dependence of the {rho} meson and pion spectral functions and self-energies is discussed. The spectral functions show considerable broadening in comparison with a perturbative calculation on the one-loop level. Using these spectral functions, we make a comparison to dilepton emission data from the CERES NA49 Collaboration employing a parametrized fireball evolution model of collision. We demonstrate that these nonperturbative finite width effects are in-medium modifications relevant to the understanding of the enhancement of the low invariant mass spectrum of dileptons emitted in A-A collisions.

Energetic Proton Emission in Heavy Ion Collisions at Intermediate Energy: Pre-Equilibrium and Cooperative Effects

Energetic proton emission has been investigated as a function of the centrality in the reaction 58Ni + 58Ni at 30 AMeV. Protons with energy extending up to a relevant fraction of the total available energy in the reaction were measured and studied. The dependence on the reaction centrality has been extensively investigated and data have been compared with the results of microscopic transport calculations. The more striking observation concerns the extremely energetic proton (ENN P ≥ 130 MeV) multiplicity which is found to increase almost quadratically with the number of participant nucleons thus indicating the onset of a mechanism beyond one and two-body dynamics.