Nuclear Theory·nucl-th

Friday·April 19, 2019

9 papers—5 primary·4 cross-listed

01
Mean-field potential effects in the cumulants of baryons from central Au+Au collision at $E_{l ab}$ = 1.23 GeV $/$ nucleon
Yongjia Wang🇨🇳 · Yunxiao Ye🇨🇳 · QIngfeng Li🇨🇳
The cumulants of baryon multiplicity distribution in relativistic heavy-ion collisions (HICs) have attracted considerable attention recently. It has been conjectured that they may serve as a promising observable to detect the critical end point in the QCD phase diagram, while the cumulants in HICs at intermediate energies have not been widely studied to date. How to interpret the cumulants data at intermediate energies and compare with the data at relativistic energies is now being actively discussed. Both meam-field potential and clustering are highly important to HICs at intermediate energies. In this talk, we discuss these effects on the cumulant ratios of baryon number distributions in Au+Au collisions at beam energies of 1.23 GeV $/$ nucleon which have been currently performed by the HADES Collaboration at GSI. Within the newest version of the ultrarelativistic quantum molecular dynamics (UrQMD) model, calculations with different mean field potentials as well as without mean field potential are performed. It is found that the mean field potential enhances fluctuations in the momentum space during the expanding stage, especially in a small rapidity acceptance window. The enhancement of cumulant ratios for free protons is suppressed compared with that for all baryons.
nucl-thhep-phAIP Conf.Proc.(2019)·0 citations
02
Two-particle angular correlations in heavy ion collisions from a multiphase transport model
Liu-Yao Zhang🇨🇳 · Jin-Hui Chen🇨🇳 · Zi-Wei Lin🇺🇸 · Yu-Gang Ma🇨🇳 · Song Zhang🇨🇳
We extend our earlier study on two-particle angular correlations in $pp$ collisions at low transverse momentum ( $p_{T}$ ) to $p$ -Pb, Pb-Pb and Au-Au collisions at RHIC and LHC energies. We mainly use the string melting version of a multiphase transport model with improved quark coalescence for this study. We start from the analysis of $π^{\pm}$ , $K^{\pm}$ and $p$ ( $p ˉ$ ) $p_{T}$ and rapidity distributions at different centralities. We then focus on two-particle angular correlations in $p$ -Pb collisions at $s_{NN} = 5.02$ TeV and Pb-Pb collisions at $s_{NN} = 2.76$ TeV. For $p$ -Pb collisions, a near side depression in the angular correlation is observed for low $p_{T}$ proton pairs and $Λ$ pairs but not for pion pairs or kaon pairs, similar to our earlier finding for $pp$ collisions at $s = 7$ TeV. This is also the case for very low multiplicity Pb-Pb and Au-Au collisions. We also find that parton interactions and the improved quark coalescence are mainly responsible for the depression feature in baryon pair angular correlations. However, no such baryon-baryon anti-correlations are observed in Pb-Pb and Au-Au collisions at higher multiplicities. Therefore our results suggest that low $p_{T}$ baryon-baryon angular anti-correlations have a strong multiplicity dependence.
nucl-thhep-phnucl-exPRC(2019)·19 citations
03
Medium Modification of Charm Production in Relativistic Heavy Ion Collisions due to Pre-equilibrium Dynamics of Partons at $s_{NN}$ = 0.2--5.02 TeV
Dinesh K. Srivastava · Rupa Chatterjee
We study the production dynamics of charm quarks in the parton cascade model for relativistic heavy ion collisions at RHIC and LHC energies. The model is eminently suited for a study of the pre-equilibrium dynamics of charm quarks at modest transverse momenta. The treatment is motivated by QCD parton picture and describes the dynamics of an ultra-relativistic heavy-ion collision in terms of cascading partons which undergo scattering and multiplication while propagating. We find considerable suppression of charm quarks production in $AA$ collisions compared to those for $pp$ collisions at the same $s_{NN}$ scaled by number of collisions. This may be important for an accurate determination of energy loss suffered by charm quarks while traversing the thermalized quark gluon plasma.
nucl-th0 citations
04
Emergence of hydrodynamical behavior in expanding quark-gluon plasmas
Jean-Paul Blaizot🇫🇷 · Li Yan🇨🇳
We use a set of simple angular moments to solve the Boltzmann equation in the relaxation time approximation for a boost invariant longitudinally expanding gluonic plasma. The transition from the free streaming regime at early time to the hydrodynamic regime at late time is well captured by the first two-moments, corresponding to the monopole and quadrupole components of the momentum distribution, or equivalently to the energy density and the difference between the longitudinal and the transverse pressures. We relate this property to the existence of fixed points in the infinite hierarchy of equations satisfied by the moments. These fixed points are already present in the two-moment truncations and are only moderately affected by the coupling to higher moments. Collisions contribute to a damping of all the non trivial moments. At late time, when the hydrodynamic regime is entered, only the monopole and quadrupole moments are significant and remain strongly coupled, the decay of the quadrupole moment being delayed by the expansion, causing in turn a delay in the full isotropization of the system. The two-moment truncation contains second order viscous hydrodynamics, in its various variants, and third order hydrodynamics, together with explicit values of the relevant transport coefficients, can be easily obtained from the three-moment truncation.
nucl-thhep-phnucl-exAnnals Phys.(2020)·76 citations
05
Excitation of the electric pygmy dipole resonance by inelastic electron scattering
V.Yu. Ponomarev · D.H. Jakubassa-Amundsen · A. Richter · J. Wambach
To complete earlier studies of the properties of the electric pygmy dipole resonance (PDR) obtained in various nuclear reactions, the excitation of the 1 $^{-}$ states in $^{140}$ Ce by $(e, e^{'})$ scattering for momentum transfers $q = 0.1 - 1.2$ ~fm $^{- 1}$ is calculated within the plane-wave and distorted-wave Born approximations. The excited states of the nucleus are described within the Quasiparticle Random Phase Approximation (QRPA), but also within the Quasiparticle-Phonon Model (QPM) by accounting for the coupling to complex configurations. It is demonstrated that the excitation mechanism of the PDR states in $(e, e^{'})$ reactions is predominantly of transversal nature for scattering angles $θ_{e} \approx 9 0^{o} - 18 0^{o}$ . Being thus mediated by the convection and spin nuclear currents, the $(e, e^{'})$ like the $(γ, γ^{'})$ reaction, may provide additional information to the one obtained from Coulomb- and hadronic excitations of the PDR in $(p, p^{'})$ , $(α, α^{'})$ , and heavy-ion scattering reactions. The calculations predict that the $(e, e^{'})$ cross sections for the strongest individual PDR states are in general about three orders of magnitude smaller as compared to the one of the lowest $2_{1}^{+}$ state for the studied kinematics, but that they may become dominant at extreme backward angles.
nucl-thnucl-exEPJA(2019)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE

Mean-field potential effects in the cumulants of baryons from central Au+Au collision at Elab​= 1.23 GeV/nucleon

Two-particle angular correlations in heavy ion collisions from a multiphase transport model

Medium Modification of Charm Production in Relativistic Heavy Ion Collisions due to Pre-equilibrium Dynamics of Partons at sNN​​= 0.2--5.02 TeV

Emergence of hydrodynamical behavior in expanding quark-gluon plasmas

Excitation of the electric pygmy dipole resonance by inelastic electron scattering

Affiliations

Mean-field potential effects in the cumulants of baryons from central Au+Au collision at $E_{l ab}$ = 1.23 GeV $/$ nucleon

Medium Modification of Charm Production in Relativistic Heavy Ion Collisions due to Pre-equilibrium Dynamics of Partons at $s_{NN}$ = 0.2--5.02 TeV