在RHIC-PHENIX中(s_(NN))~(1/2)=200GeV Au Au碰撞中直接光子的椭圆流测量(英文)

Azimuthal anisotropy of direct photon is measured in S_(NN)~(1/2)=200GeV Au Au collisions at RHIC- PHENIX.Direct photon is one of the most effective probes to study properties of hot dence medium at initial state(also QGP state)of heavy ion collisions because photons almost do not interact strongly with any other particles caused by its long mean free path and they keep their conditions when they axe created.Within statistical and systematic errors,the elliptic flow parameter(v_2)of direct photon is consistent with zero. Direct photon v_2 is estimated by hadron decay photon contamination are subtracted from inclusive photon v_2 in intermediate to high transverse momentum(p_T)region(0 to 10GeV/c)for 3 centrality selections(20% steps)and minimum bias.     

金核——金核与质子-质子对撞中矢量介子K0(892)和φ(1020)的自旋排列

We present the preliminary results on the spin alignment matrix element ρ₀₀ for vector mesons K^*0(892) and φ(1020) in mid-central (20%—60%) Au+Au and p+p collisions at s_NN=200GeV. The values of ρ₀₀ with respect to reaction plane in Au+Au collisions are 0.36±0.02(stat)±0.13(sys) for K^*0(892) and 0.38±0.01 (stat)±0.04 (sys) for φ(1020). No evident global spin alignment with respect to reaction plane is observed in the measured p_T region up to 5GeV/c with current sensitivity. ρ₀₀ with respect to the production plane of the vector meson is also measured for K^*0(892) and φ(1020) in Au+Au collisions, and for φ(1020) in p+p collisions. No significant difference for the ρ₀₀ between Au+Au and p+p collisions is observed with our data sample.     

200GeV AuAu碰撞中前快度区的微分椭圆流

Identified particle elliptic flow results are presented for the Au+Au reaction at s_NN=200GeV as a function of transverse momentum and pseudorapidity. Data at pseudorapidities η≈0,1, and 3.4 were obtained using the two BRAHMS spectrometers. Differential v₂ (η,p_t) values for a given particle type are found to be essentially constant over the covered pseudorapidity range, in contrast to the integral v₂ values which have previously been observed to decrease at forward rapidities. A softening of the particle spectra at forward angles is found to account for at least part of the integral v₂ falloff. The data are found to be consistent with existing constituent quark scaling systematics.     

Λ-超子在RHIC的Au+Au碰撞中的整体极化

We present the Λ-hyperon global polarization in Au+Au collisions at s_NN=62GeV and 200GeV measured with the STAR detector at RHIC. The observed Λ-hyperon global polarization is consistent with zero, what is in agreement with recent measurements of Λ global polarization, as well as φ(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%.     

Eccentricity and elliptic flow at fixed centrality in Au+Au collisions at √<SPAN style=

In this paper, elliptic flow is studied at fixed centrality in Au+Au collision at √s_NN=200 GeV in the AMPT model. It is observed that with the participant increasing, elliptic flow has an increase or a decrease at different fixed impact parameter, but it does not have a trivial fluctuation. It is analyzed that the initial space anisotropy dominates the participant dependence of elliptic flow in near-central collisions(b=5 fm) and mid-central collisions(b=8 fm), while the interaction between particles can mainly answer for the behavior of elliptic flow with participant in peripheral collisions (b=12 fm). To distinguish the pure geometrical effect, elliptic flow scaled by initial eccentricity is studied. It is found that the ratio v₂/ε increases with participant and reaches a saturation when the participant is large enough, indicating that the collision system may reach the local equilibrium.     

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

The centrality dependence of transverse momentum spectra for identified hadrons at midrapidity in Au+Au collisions at √s_NN= 200GeV is systematically studied in a quark combination model. The p_T spectra of π^±, K^±, p(p) and Λ(Λ) in different centrality bins and the nuclear modification factors (R_CP) 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 p_T spectra and the R_CP for π⁰, K_s⁰ and Λ in Cu+Cu collisions at √s_NN= 200GeV are well described. The results show that 〈β(r)〉 is only a function of the number of participants N_part and it is independent of the collision system.     

在RHIC-PHENIX中观测到的AuAu和CuCu碰撞中已鉴别强子产物的标度率特性

Particle type dependences of hadron yield and emission patterns, especially its difference between mesons and baryons, at intermediate p_{T(2—5GeV/c) is one of the findings in heavy ion collisions at RHIC. A systematic study of identified hadron production was performed in Au+Au/Cu+Cu collisions at sNN=62.4/200GeV, to investigate the possible origins of this difference. In this paper, we show particle ratios, elliptic flow strengths, and their scaling properties.}     

Various flows of black and grey particles produced in Mg-emulsion collisions at 4.5 A GeV/c

Various flow phenomena of black particles (b-particles) and grey particles (g-particles) produced in magnesium-emulsion (Mg-Em) collisions at 4.5 A GeV /c are reported. These flows are directed and elliptic transverse flows (v₁ and v₂) related by the azimuthal angle (φ), directed and elliptic reaction plane flows (v_R1 and v_R2) related by the projected angle (ψ) on the reaction plane, and directed and elliptic polar direction flows (v_P1 and v_P2) related by the polar angle (θ). We extract absolute flows as the direct experimental values minus the isotropic theoretical values. The dependence of the various flows on the target particle multiplicity and on the angles (θ,φ,ψ) is investigated. Our results show that the dependence of b-particle flows on the target size is obvious and for heavy targets the dependence on target particle multiplicity is slight. Compared with b-particles, g-particles have a slight dependence on the target size and target particle multiplicity.     

Jet production at next-to-leading order in p+Au collisions at the RHIC

We calculate jet productions in p+Au collisions at the RHIC at next-to-leading order with perturbative QCD. Inclusive jet transverse energy spectrum, dijet invariant mass spectrum, dijet angular distribution, and corresponding nuclear modification factors for the three observables in p+Au collisions at √s=200 GeV are given, where the initial-state cold nuclear matter (CNM) effects are included by taking advantage of four parametrization sets of nuclear parton distribution functions (nPDFs) - EPS, nCTEQ, HKN and DS. We demonstrate that inclusive jet transverse energy (E_T) spectrum, dijet invariant mass (M_JJ) spectrum with all 4 nPDFs are increased at low E_T or M_JJ, whereas at high E_T or M_JJ large deviation of results with different nPDFs is observed. It is found that the dijet angular distributions in p+Au collisions do not vary relative to those in p+p collisions for all 4 nPDFs.     

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.     

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.     

Pseudorapidity distribution of multiplicity in Au+Au collisions at √sNN=200GeV

Using the Glauber model, we discuss the number of binary nucleon-nucleon collisions in heavy-ion collisions. Based on the latter, after considering the effect of energy loss of the nucleons in multiple collisions, we derive the pseudorapidity distribution of the multiplicity as a function of the impact parameter in nucleus-nucleus collisions. Using this, we analyze the experimental measurements carried out by the BRAHMS Collaboration in Au+Au collisions at √s_NN=200GeV. The results are in good agreement with the experimental observations.     

金核-金核与质子-质子对撞中矢量介子K*0(892)和φ(1020)的自旋排列

We present the preliminary results on the spin alignment matrix elementρ_(00)for vector mesons K~(*0)(892)andφ(1020)in mid-central(20%—60%)Au Au and p p collisions at S_(NN)~(1/2)=200GeV.The values ofρ_(00)with respect to reaction plane in Au Au collisions are 0.36±0.02(stat)±0.13(sys)for K~(*0)(892)and 0.38±0.01(stat)±0.04(sys)forφ(1020).No evident global spin alignment with respect to reaction plane is observed in the measured p_T region up to 5GeV/c with current sensitivity,ρ_(00)with respect to the production plane of the vector meson is also measured for K~(*0)(892)andφ(1020)in Au Au collisions,and forφ(1020)in p p collisions.No significant difference for theρ_(00)between Au Au and p p collisions is observed with our data sample.     

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.     

Squeezed back-to-back correlations of K~+K~- in d+Au collisions at sNN~(1/2)=200 GeV and Au+Au collisions at sNN~(1/2)=62.4 GeV

We investigate the squeezed back-to-back correlations(BBC) of K~+K~-, caused by the mass modification of particles in the dense medium formed in d + Au collisions at sNN~(1/2)= 200 GeV and Au + Au collisions at sNN~(1/2)= 62.4 GeV. Considering that some kaons may not be affected by the medium, we further study the BBC functions of K~+K~-when parts of all kaons have a mass-shift. Our results indicate that the BBC functions of K~+K~-can be observed when only ～10% of all kaons have a mass-shift in d + Au collisions at sNN~(1/2) = 200 GeV and the peripheral collisions of Au + Au at sNN~(1/2)= 62.4 GeV. Since the BBC function is caused by the mass-shift due to the interactions between the particle and the medium, the successful detection of the BBC function indirectly marks that the dense medium has formed in these collision systems. We suggest the experimental measurement of the BBC function of K~+K~- in d + Au collisions at sNN~(1/2) = 200 GeV and peripheral collisions of Au + Au at sNN~(1/2) = 62.4 GeV.     

Impact parameter and beam energy dependence for azimuthal asymmetry of direct photons and free protons in intermediate energy heavy-ion collisions

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have calculated the impact parameter and beam energy dependence for azimuthal asymmetry, characterized by directed transverse flow parameter F and elliptic asymmetry coefficient v₂, of direct photons and the corresponding free protons in intermediate energy heavy-ion collisions. It is further shown the anti-correlated azimuthal asymmetry between direct photons and free protons.     

Drell-Yan dilepton production in relativistic heavy-ion collisions at RHIC

We investigate the lepton pair production with the Drell-Yan process in relativistic heavy ion collisions by computing the double differential cross section dσ/dM²dy and dσ/dM²dx_F at the next-to-leading order in p+Au and Au+Au collisions with √s_NN =200 GeV at RHIC. The resulting nuclear modification factors R^pAu and R^AuAu show strong sensitivity to the cold nuclear matter (CNM) effects and could probe the CNM effects at a very wide region of the longitudinal momentum fraction x. The variation of R with the invariant mass M, the rapidity y and the Feynman variable x_F is shown and we find that the nuclear modification factor for the double differential cross section could be smaller than 0.4 in some kinematic regions of high-energy nucleus-nucleus reactions at RHIC.     

FIRST-PRINCIPLE SELF-CONSISTENT PSEUDOPOTENTIAL CALCULATION OF THE ELECTRONIC STRUCTURES OF SHORT-PERIOD (GaAs)m(AlAs)n SUPERLATT1CES

With the local density approximation, the band structares of the short-period (GaAs)₁(AlAs)₁ and (GaAs)₂(AlAs)₁ superlattices are calculated by using the first-principle self-consistent pseudopotential method. The results show that the (GaAs)₁(AlAs)₁ superlattice is an indirect semiconductor, and the lowest conduction band state is at point R in the Brillouin zone; the (GaAs)₂(AlAs)₁ superlattice is a direct semiconductor and the lowest conduction band state is at point Γ. The squared matrix elements of transition are calculated. The pressure coefficients of energy gaps of the (GaAs)₁(AlAs)₁ and (GaAs)₂(AlAs)₁ superlattices are calculated and compared with those obtained by hydrostatic pressure experiments.     

Hadronic rapidity spectra in heavy ion collisions at SPS and AGS energies in a quark combination model

The quark combination mechanism of hadron production is applied to nucleus-nucleus collisions at the CERN Super Proton Synchrotron (SPS) and the BNL Alternating Gradient Synchrotron (AGS). The rapidity spectra of identified hadrons and their spectrum widths are studied. The data of π^-, K^±, φ, Λ, Λ, Ξ^- and Ξ⁺ at 80 and 40 A GeV, and in particular at 30 and 20 A GeV where the onset of deconfinement is suggested to happen, are consistently described by the quark combination model. However, at AGS 11.6 A GeV below the onset, the π^±, K^± and Λ spectra cannot be simultaneously explained, indicating the disappearance of the intrinsic correlation of their production in the constituent quark level. The collision-energy dependence of the rapidity spectrum widths of the constituent quarks, and the strangeness of the hot and dense quark matter produced in heavy ion collisions, are obtained and discussed.     

-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%.