Nuclear Theory·nucl-th

Friday·June 18, 2021

13 papers—6 primary·7 cross-listed

01
Polarization tensor of magnetized quark-gluon plasma at nonzero baryon density
Xinyang Wang🇨🇳 · Igor Shovkovy🇺🇸
We derive a general expression for the absorptive part of the one-loop photon polarization tensor in a strongly magnetized quark-gluon plasma at nonzero baryon chemical potential. To demonstrate the application of the main result in the context of heavy-ion collisions, we study the effect of a nonzero baryon chemical potential on the photon emission rate. The rate and the ellipticity of photon emission are studied numerically as a function the transverse momentum (energy) for several values of temperature and chemical potential. When the chemical potential is small compared to the temperature, the rates of the quark and antiquark splitting processes (i.e., $q \to q + γ$ and $q ˉ \to q ˉ + γ$ , respectively) are approximately the same. However, the quark splitting gradually becomes the dominant process with increasing the chemical potential. We also find that increasing the chemical potential leads to a growing total photon production rate but has only a small effect on the ellipticity of photon emission. The quark-antiquark annihilation ( $q + q ˉ \to γ$ ) also contributes to the photon production, but its contribution remains relatively small for a wide range of temperatures and chemical potentials investigated.
nucl-thhep-phhep-thEPJC(2021)·27 citations
02
Level Densities from 0-30 MeV
R.B. Firestone
Photon strength, $f (E_{γ})$ , measured in photonuclear reactions, is the product of the average level density per MeV, $ρ (E_{x})$ , and the average reduced level width, $Γ_{γ} / E_{γ}^{3}$ for levels populated primarily by E1 transitions at an excitation energy $E_{x} = E_{γ}$ . It can be calculated with the Brink-Axel (BA) formulation modified to include contributions from the Giant Dipole Resonance (GDR) and higher lying resonances. Level densities and reduced widths have been calculated for 17 nuclei with atomic numbers between Z=14-92. Level densities below the GDR energy were calculated with the CT-JPI model and combined with the BA photon strength to determine the associated reduced widths. The reduced widths varied exponentially with level energy and could be extrapolated up to higher energies. The extrapolated widths were then combined with the BA photon strength to determine the level densities at higher energies. The level densities are found to increase exponentially at low energies, peak near the GDR energy due to the appearance of new states at the $2ℏ ω$ shell closure, and continue to increase less rapidly up to at least 30 MeV. The average level densities have been compared with the Fermi Gas Level Density (FGLD), Back-Shifted Fermi Gas (BSFG), and Hartree-Fock-Bogoliubov (HFB) models. Good agreement is found with the nearly identical FGLD and BDFG models, while the HFB models gives substantially lower level densities. A universal set of FGLD model parameters were determined as a function of mass and temperature that are applicable to all nuclei.
nucl-thnucl-ex1 citation
03
Continuous evolution of electromagnetic field in heavy-ion collisions
Evan Stewart🇺🇸 · Kirill Tuchin🇺🇸
In heavy-ion collisions the electromagnetic field exists before the hot nuclear matter emergence. Requiring the field continuity we compute it in the central rapidity region by taking into account the electromagnetic response of the Quark Gluon Plasma. We show that the electromagnetic field is nearly time-independent from about 1~fm/c after the collision until the freezeout.
nucl-thhep-phNPA(2021)·26 citations
04
Semi-microscopic construction of multi- $α$ cluster spaces
J. R. M. Berriel-Aguayo🇲🇽 · P. O. Hess🇲🇽
An approximate but straight forward projection method to molecular many alpha-particle states is proposed and the overlap to the shell model space is determined. The resulting space is in accordance with the shell model, but still contains states which are not completely symmetric under permutations of the alpha-particles, which is one reason to call the construction semi-microscopic. A new contribution is the construction of the 6- and 7- $α$ -particle spaces. The errors of the method propagate toward larger number of alpha-particles and larger shell excitations. In order to show the effectiveness of the construction proposed, the so obtained spaces are applied, within an algebraic cluster model, to $^{20}$ Ne, $^{24}$ Mg and $^{28}$ Si, each treated as a many-alpha-particle system. Former results on $^{12}$ C and $^{16}$ O are resumed.
nucl-thPRC(2021)·3 citations
05
Global spin polarization of multistrange hyperons and feed-down effect in heavy-ion collisions
Hui Li🇨🇳 · Xiao-Liang Xia🇨🇳 · Xu-Guang Huang🇨🇳 · Huan Zhong Huang🇨🇳
Global spin polarization of hyperons is an important observable to probe the vorticity of the quark-gluon plasma produced in heavy-ion collisions. We calculate the global polarizations of $Λ$ , $Ξ^{-}$ , and $Ω^{-}$ in Au+Au collisions at energies $s_{NN} =$ 7.7--200 GeV based on a multiphase transport model. Our calculations suggest that their primary global polarizations fulfill $P_{Ω^{-}} ≃ 5/3 P_{Ξ^{-}} ≃ 5/3 P_{Λ}$ . We also estimate the feed-down effect of particle decay on the global polarization. With the feed-down effect taken into account, the global polarizations of $Λ$ and $Ξ^{-}$ are clearly separated, and the final global polarizations are in the ordering: $P_{Ω^{-}} > P_{Ξ^{-}} > P_{Λ}$ . Such a relation can be tested in experiments, which will provide us more information about the global polarization mechanism.
nucl-thPLB(2022)·37 citations
06
Investigations of the linear and non-linear flow harmonics using the A Multi-Phase Transport model
Niseem Magdy🇺🇸
The Multi-Phase Transport model (AMPT) is used to study the effects of the parton-scattering cross-sections ( $σ_{pp}$ ) and hadronic re-scattering on the linear contributions to the flow harmonic $v_{4}$ , the non-linear response coefficients, and the correlations between different order flow symmetry planes in Au+Au collisions at 200~GeV. The model results, which agree with current experimental measurements, indicate that the higher-order flow harmonics are sensitive to the $σ_{pp}$ variations. However, the non-linear response coefficients and the correlations between different order flow symmetry planes are $σ_{pp}$ independent. These results suggest that further detailed experimental measurements which span a broad range of collision systems and beam energies could serve as an additional constraint for the theoretical models' calculations.
nucl-thhep-phnucl-exJ.Phys.G(2022)·10 citations

Affiliations

first authorsco-authorsvia INSPIRE

Polarization tensor of magnetized quark-gluon plasma at nonzero baryon density

Level Densities from 0-30 MeV

Continuous evolution of electromagnetic field in heavy-ion collisions

Semi-microscopic construction of multi-α cluster spaces

Global spin polarization of multistrange hyperons and feed-down effect in heavy-ion collisions

Investigations of the linear and non-linear flow harmonics using the A Multi-Phase Transport model

Affiliations

Semi-microscopic construction of multi- $α$ cluster spaces