Simulation of energy scan of pion interferometry in central Au+Au collisions at relativistic energies

We present a systematic analysis of two-pion interferometry for the central Au+Au collisions at √s_NN=3, 5, 7, 11, 17, 27, 39, 62, 130 and 200 GeV/c with the help of a multiphase transport (AMPT) model. Emission source-size radius parameters R_long, R_out, R_side and the chaotic parameter λ are extracted and compared with the experimental data. Transverse momentum and azimuthal angle dependencies of the HBT radii are also discussed for central Au+Au collisions at 200 GeV/c. The results show that the HBT radii in central collisions do not change much above 7 GeV/c. For central collisions at 200 GeV/c, the radii decrease with the increasing of transverse momentum p_T but are not sensitive to the azimuthal angle. These results provide a theoretical reference for the energy scan program of the RHIC-STAR experiment.     

Rapidity dependence of hadron PT spectra in central Au＋Au collisions at √^SNN = 200 GeV

The transverse momentum spectra for identified hadrons at different rapidities in central Au＋Au collisions at √^SNN= 200 GeV are studied in a quark combination model. The results for PT spectra of π^±, K^±, p（p^-） and for the p/π ratios in a broader PT range at midrapidity agree well with the data. The transverse momentum spectra of pions, protons and antiprotons at various rapidities y - 1, η= 2.2 and y ≈ 3.2 are calculated and compared with the data.     

Rapidity dependence of hadron PT spectra in central Au+Au collisions at = 200 GeV

The transverse momentum spectra for identified hadrons at different rapidities in central Au+Au collisions at = 200 GeV are studied in a quark combination model. The results for PT spectra of π±,K±, p(p-) and for the p/π ratios in a broader PT range at midrapidity agree well with the data. The transverse momentum spectra of pions, protons and antiprotons at various rapidities y 1, η= 2.2 and y≈3.2 are calculated and compared with the data.     

Effects of a phase transition on two-pion interferometry in heavy ion collisions at■=2.4-7.7 GeV

Hanbury-Brown-Twiss(HBT) correlations for charged pions in central Au+Au collisions at■=2.4-7.7 GeV(corresponding to beam kinetic energies in the fixed target frame from E_lab=1.23 to 30 GeV/nucleon) are calculated using the ultra-relativistic quantum molecular dynamics model with different equations of state(EoSs).The effects of a phase transition at high baryon densities are clearly observed in the explored HBT parameters.The results show that the available data on the HBT radii,R     

Properties of Dihadron Correlations for p＋p Collisions at √8NN = 200 GeV

The dihadron azimuthal angular correlations for p＋p collisions at √8NN = 200 GeV are simulated by a multiphase transport model. The dispersions of near-side and away-side peaks, indicated by the width of Gaussian fit functions and the rms width, decrease with the transverse momentum of associated particles. This trend is consistent with the experimental results. Conditional-yields are also calculated to obtain distributions of the associated particle transverse momentum for both away-side and near-side. Furthermore, the hadronic rescattering effects make the conditional-yield distributions softer.     

Properties of Dihadron Correlations for p+p Collisions at √sNN= 200 GeV

The dihadron azimuthal angular correlations for p+p collisions at√s_NN=200 GeV are simulated by a multi-phase transport model. The dispersions of near-side and away-side peaks, indicated by the width of Gaussian fit functions and the rms width, decrease with the transverse momentum of associated particles. This trend is consistent with the experimental results. Conditional-yields are also calculated to obtain distributions of the associated particle transverse momentum for both away-side and near-side. Furthermore, the hadronic rescattering effects make the conditional-yield distributions softer.     

Baryonic Effect on χcJ Suppression in Au＋Au Collisions at RHIC Energies

We predict that χcJ mesons at low transverse momentum in the central rapidity region are almost dissociatedby nucleons and antinucleons in hadronic matter produced in central Au Au collisions at relativistic high-ioncollider (RHIC) energies √^sNN = 130 and 200 GeV. In the calculations the nucleon and antinucleon distributionsin hadronic matter are results of evolution from their freeze-out distributions which well fit the experimentaltransverse momentum spectra of proton and antiproton.     

Centrality dependence of pT spectra for identified hadrons in Au Au and Cu Cu collisions at (~SNN)~(1/2)=200 GeV

The centrality dependence of transverse momentum spectra for identified hadrons at midrapidity in Au Au collisions at (~SNN)~(1/2) = 200GeV is systematically studied in a quark combination model. The pT spectra of π±, K±, p() and Λ(■) in different centrality bins and the nuclear modification factors (RCP) for these hadrons are calculated. The centrality dependence of the average collective transverse velocity β (r) for the hot and dense quark matter is obtained in Au Au collisions, and it is applied to a relative smaller Cu Cu collision system. The centrality dependence of pT spectra and the RCP for π0, Ks0 and Λ in Cu Cu collisions at (~SNN)~(1/2) =200 GeV are well described. The results show that β(r) is only a function of the number of participants Npart and it is independent of the collision system.     

Φ Meson Production in Heavy Ion Collisions at RHIC

We present Φ meson production in Cu+Cu and Au+Au collisions measured by the STAR experiment at RHIC.The hadronic decay mode Φ→K~+K~- is used in the analysis.The yields for Φ meson in Cu+Cu and Au+Au collisions at a given beam energy are scaled by the number of participant.The N_(part) normalized Φ meson yields in heavy ion collisions over those from p+p collisions are larger than 1 and increase with collision energy.These results suggest that the source of enhancement of strange hadrons is related to the formation of a dense medium in high energy heavy ion collisions and can not be only due to canonical suppression of their production in smaller systems.We also present STAR results on the Φ meson elliptic flow υ_2 from 2~(1/SNN)=200 GeV Cu+Cu at RHIC.The elliptic flow in Cu+Cu system that has the similar relative magnitude and qualitative features as that in Au+Au system.The observations imply the hot and dense matter with partonic collectivity has been formed in heavy ion collisions at RHIC.However,eccentrality normalized υ_2,υ_2/(n_qε_(part)) is lower for Cu+Cu than for Au+Au collisions at 200 GeV.So this might indicate thermalization has not been reached in 200 GeV Cu+Cu collisions.     

Centrality dependence of pT spectra for identified hadrons in Au+Au and Cu+Cu collisions at √SNN=200 GeV

The centrality dependence of transverse momentum spectra for identified hadrons at midrapidity in Au+Au collisions at √SNN=200GeV is systematically studied in a quark combination model.The pT spectra of π±,K±,P(p-)and A(A)in different centrality bins and the nuclear modification factors(Rcp)for these hadrons are calculated.The centrality dependence of the average collective transverse velocity(β(r)) for the hot and dense quark matter is obtained in Au+An collisions,and it is applied to a relative smaller Cu+Cu collision system.The centrality dependence of pT spectra and the Rcp for π0,K0/s and A in Cu+Cu collisions at √SNN=200 GeV are well described.The results show that(β(r))is only a function of the number of participants Npart and it is independent of the collision system.     

Trace initial interaction from final state observable in relativistic heavy ion collisions

In order to trace azimuthal angle dependence of the initial interaction in ultra-relativistic heavy ion collision, two azimuthal multiplicity-correlation patterns neighboring and fixed-to-arbitrary angularbin correlation patterns -- are suggested. From the simulation of Au ＋ Au collisions at √SNN = 200 GeV by using the Monte Carlo models RQMD with hadron re-scattering and AMPT with and without string melting, we observe that the correlation patterns change gradually from out-of-plane preferential one to inplane preferential one when the centrality of collision shifts from the central collision to peripheral collision, meanwhile the anisotropic collective flow v2 keeps positive in all cases. This regularity is found to be collision energy independent. The physics behind the two opposite trends of correlation patterns, in particular, the presence of out-of-plane correlation patterns at RHIC energy, are discussed.     

Multiparticle azimuthal correlations in central nucleus-nucleus collisions at high energy

Multiparticle azimuthal correlations in central nucleus-nucleus collisions at high energy are described by a simple formula. The calculated results are in agreement with the experimental data of carbon and oxygen induced interactions at Dubna energy. The comparison between the calculated results and experimental data shows that particles are emitted isotropically in the rest frame of the emission sources, and the emission sources have movements in momentum space.     

Size of the freeze-out source in high energy heavy ion collisions

Based on a hydro-inspired azimuthally symmetric emission function, we analyze the HBT radius R_s and the single-particle transverse momentum spectra in Au+Au collisions measured by the STAR Collaboration at √s_NN=200 GeV. The results show that consistent assumptions about transverse density (and/or flow profile) in the calculation of the HBT radius R_s and single-particle spectral analyses play an important role for understanding the size of the freeze-out source.     

Emissions of fragments and mesons produced in heavy-ion collisions at CSR and related energies

Using a multisource ideal gas (MSIG) model, we reconstruct the transverse emission source in the momentum space for light fragments produced in reactions ⁸⁶Kr-¹²⁴Sn at 25 MeV/nucleon and b=7—10 fm based on the theoretical predictions of the Isospin-Dependent Quantum Molecular Dynamics (IDQMD) model. We show that the MSIG model can reasonably describe the IDQMD-predicted results for the azimuthal distribution and the transverse momentum dependence of elliptic flow v₂ and fourth-order anisotropic flow v₄ but can only qualitatively describe the transverse momentum spectra. The azimuthal distributions of nuclear fragments produced in heavy-ion collisions at intermediate energies are studied by the MSIG model. The calculated results are compared and found to be in agreement with the experimental data of Ca-Ca, Nb-Nb, and Au-Au collisions at 150—800 MeV/nucleon beam energies. Meanwhile, the angular distributions of pions and kaons produced in heavy-ion collisions at the low-energy end (1—2 GeV/nucleon) of high energies are investigated by the MSIG model, too. The calculated results are compared and found to be in agreement with the experimental data of the KaoS Collaboration.     

Search for the origin of double-peak structure at RHIC by AMPT model with triggered di-jet

With a multi-phase transport （AMPT） model,a γ-jet with known production point and momentum is triggered to search for the origin of double-peak structure in di-hadron azimuthal correlation in central Au＋Au collisions at RHIC energy.The different configurations of triggered γ-jet produce different shapes of medium responses.The key of the double-peak structure is found to be a strong shadowing effect of dense core,which is related to transverse expansion and radial flow of partonic matter.     

-超子在RHIC的Au Au碰撞中的整体极化(英文)

We present the-hyperon global polarization in Au Au collisions at S_(NN)~(1/2)=62GeV and 200GeV measured with the STAR detector at RHIC.The observed(?)-hyperon global polarization is consistent with zero, what is in agreement with recent measurements of A global polarization,as well asφ(1020)and K~(*0)(892)vector mesons spin alignment with respect to the reaction plane.The possible dependence of the global polarization on relative azimuthal angle between the orbital momentum of the system and the hyperon 3-momentum is discussed.The corresponding systematic uncertainty due to detector acceptance is found to be less than 20%.     

Azimuthal distributions of radial momentum and velocity in relativistic heavy ion collisions

Azimuthal distributions of radial (transverse) momentum, mean radial momentum, and mean radial velocity of final-state particles are suggested for relativistic heavy ion collisions. Using the AMPT transport model with string melting, the distributions of Au+Au collisions at 200 GeV are presented and studied. It is demonstrated that the distribution of total radial momentum is more sensitive to the anisotropic expansion, as the anisotropies of final-state particles and their associated transverse momentums are both counted in the measurement. The mean radial velocity distribution is compared with the radial flow velocity. The thermal motion contributes an isotropic constant to the mean radial velocity.     

Effects of Surface Emitting and Cumulative Collisions on Elliptic Flow

The integral and differential elliptic flow of partons is calculated using the multiphase transport model for Au＋Au collisions at centre-of-mass energy √SNN=200 GeV. It is shown that elliptic flow of partons freezing out at early time, which is affected mainly by surface emittance, decreases with time and elliptic flow of partons freezing out at late time, which is dominated by cumulative collisions, increases with time. The elliptic flow of partons freezing out early has a large contribution to the flatting of curve of final differential elliptic flow at large transverse momentum. It is argued that the effect of surface emittance is not neglectable.     

Effects of bulk viscosity on hadron spectra and the Hanbury-Brown Twiss radius by causal viscous hydrodynamics

The particle spectra and Hanbury-Brown Twiss (HBT) radius of Au+Au collisions at RHIC energy are investigated by a hydrodynamical expanding source with both shear and bulk viscosities ($\zeta$). With a large width of the ratio of $\zeta$ to entropy density s, both the particle transverse momentum spectra and the ratio R_\rm out/R_\rm side of HBT radii in the direction of the total transverse momentum of detected two particles (R_\rm out) and perpendicular to both this direction and the beam direction (R_\rm side) become a little steeper.     

Strange particle production in relativistic nucleus-nucleus collisions at RHIC and LHC energy regions

PACIAE, a parton and hadron cascade model, is utilized to systematically investigate strange particle production and strangeness enhancement in Au＋Au collisions and in Pb＋Pb collisions with the √SNN = 200 GeV at the RHIC and 2.76 TeV at the LHC, respectively. The experimental results at different centralities, using data from the STAR collaboration and the ALICE collaboration, are well described by the PACIAE model. This may represent the importance of the parton and hadron rescatterings, as well as the reduction mechanism for strange quark suppression, that are implemented in the PACIAE model.