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.     

A Non-Zero Hadronic Elliptic Flow with a Vanished Partonic Elliptic Flow in a Coalescence Scenario

The elliptic flow of a hadron is calculated using a quark coalescence model based on the quark phase space distribution produced by a free streaming locally thermalized quark in a two-dimensional transverse plane at initial time. Without assuming the quark＇s elliptic flow, it is shown that the hadron obtains a non-zero elliptic flow in this model. The elliptic flow of the hadron is shown to be sensitive to both space momentum correlation and the hadron＇s internal structure. Quark number scaling is obtained only for some special cases.     

Effects of multi-collisions and surface on elliptic flow

The non-central Au+Au collision at center-of-mass energy √s_NN=200 GeV is simulated using AMPT model. It is found that both the integral and differential elliptic flow behaves differently for partons freezing out at different stages. It is shown that the integral elliptic flow of freeze-out partons decreases with time at the early stage, but increases with time at the late stage. The curve of transverse momentum distribution of elliptic flow of partons is more flatter at the early stage than at the late stage. The effect of surface emitting on elliptic flow is argued to be not neglectable.     

The production of slow particles in 16O－Em interactions at 4.5 A GeV/c

A sample of 1233 events is used to study the general characteristics of {}^{16}O－Em interactions at 4.5 A GeV/c. Multiplicity and angular distributions of slow particles and correlations among them are discussed. The present data are compared with the corresponding results from the interactions of other projectiles at the same energy and also the same projectile at different energies. The results indicate that black particle production is independent of the energy and mass of the projectile, but for grey particles it is dependent on the mass of projectile.     

等离子体密度对激光拉曼放大机理的影响

等离子体中的背向拉曼散射机理可以用来产生超短超强的激光脉冲. 本文采用粒子模拟方法模拟研究了等离子体密度对激光拉曼放大过程的影响. 研究发现, 过低的等离子体密度会导致等离子体波提前波破而降低能量转换效率; 而过高的等离子体密度又会导致其他不稳定性的快速增长, 限制作用距离和输出能量. 因此, 拉曼放大机理的最佳等离子体密度应处于等离子体波破的密度阈值附近, 可以获得最高的能量转换效率和能量输出. 另外, 空间频谱分析显示放大激光的强度饱和主要来自于自相位调制不稳定性的发展. 利用10¹³ W·cm^-2的抽运激光脉冲, 模拟证实拉曼放大机理可有效地将种子激光的强度从10¹³ W·cm^-2 放大到10¹⁷ W·cm^-2, 脉宽压缩到40 fs, 且能量转换效率达到58%.     

Production of helium projectile fragments in {16O－emulsion interactions at 4.5 A GeV/c

The measurements of partial production cross sections of the multiple helium projectile fragments emitted at 4.5 A GeV/c {}^{16}O－Em interactions are reported. We have studied the production rate of helium projectile fragments due to fragmentation of {}^{16}O ions and compared it with that obtained from different projectiles at various energies. The dependence of on the mass number of the incident beams is formulated. The multiplicity distributions of the helium fragments produced in {}^{16}O－Em interactions at different energies exhibit Koba－Nielson－Olesen (KNO) scaling. The correlation of helium projectile fragments and target fragments is also investigated and it is found that the average of target fragments is increased with the decrease of the number of helium fragments in peripheral interactions.     

Space-momentum correlations in 8 AGeV Au+Au collisions

Within the RQMD model, space-momentum correlations, i.e. the correlations between final momentum anisotropy and initial eccentricity, are studied for 8 AGeV Au＋Au events classified according to the multi-particle azimuthal correlations. The results show that the final elliptic flow fluctuations depend on the initial collision geometry. There are clear space-momentum correlations for nucleons during the whole dynamical evolution of the collisions.     

Electromagnetic dissociation of 3.7 A GeV^16O in nuclear emulsion

The electromagnetic dissociation (ED) of 3.7 A GeV {}^{16}O in nuclear emulsion is investigated with high statistics. It is found that the electromagnetically dissociated cross section increases with increasing beam energy, the charge distribution of projectile fragments is the same as the results at 60 and 200 A GeV, and the production probability of projectile fragments with charge 3≤Z≤5 is less than that of the other projectile fragments. These results can be well explained by use of Weizsacker and Williams method for calculating the ED contributions. The percentile abundance of various decay modes for ED at 3.7 A GeV is close to the result at 60 and 200 A GeV, but it is different from the result at 14.6 A GeV. The ED of 3.7 A GeV is mainly caused by the giant dipole and quadrupole resonance of E1 and E2, which can be qualitatively explained by the multiplicity distribution of projectile proton in ED. The multiplicity distribution of the α fragments in ED and nuclear events have different functional forms. This difference may be a consequence of the different reaction mechanism involved.     

强激光与锥型结构靶相互作用准直电子束粒子模拟研究

利用PIC(particle-in-cell)方法模拟研究了超短强激光与锥型三明治结构靶相互作用快电子束的产生和传输,并与锥通道靶、锥丝靶和锥靶在相同激光参数下的作用结果进行了比较.研究发现强激光与锥三明治靶作用产生的快电子能被不同密度材料产生的准静态界面强磁场有效地准直传输.相对其他三种锥型结构靶,锥三明治靶能产生更多数目及更高能量的快电子,提高了激光到快电子的能量转换效率和快电子束的品质,这对快点火能量沉积是有利的.     

皮秒短脉冲X射线背光诊断快点火靶丸压缩面密度

为了给快点火集成耦合效率的计算提供关键参数,并为后期高密度压缩奠定高能背光的诊断基础,在神光-Ⅱ升级装置上利用皮秒短脉冲激光驱动产生了X射线背光源,测量了成像分辨率、光通量,获得了短脉冲背光源的辐射特性,进一步成功演示了基于这种短脉冲背光照相技术的间接驱动快点火预压缩密度诊断。实验所得图像与模拟图像结构一致,实测压缩过程中的面密度达到50 mg/cm2。实验还发现了压缩不对称引起的流体不稳定性特征,为后续实验提供了改进方向。