Systematics of central heavy ion collisions in the 1A GeV regime

Using the large acceptance apparatus FOPI, we study central collisions in the reactions (energies in A GeV are given in parentheses): Ca-40 + Ca-40 (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), Ni-58 + Ni-58 (0.15, 0.25, 0.4), Ru-96+Ru-96 (0.4, 1.0. 1.5), (96)zr+(96)zr 1.0, 1.5), Xe-129+CsI (0.15, 0.25, 0.4), Au-197 + Au-197 (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include cluster multiplicities, longitudinal and transverse rapidity distributions and stopping, and radial flow. The data are compared to earlier data where possible and to transport model simulations. (C) 2010 Elsevier B.V. All rights reserved.

Probing high-density behavior of symmetry energy from pion emission in heavy-ion collisions

Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, the emission of pion in heavy-ion collisions in the region 1 A GeV as a probe of nuclear symmetry energy at supra-saturation densities is investigated systematically, in which the pion is considered to be mainly produced by the decay of resonances Delta(1232) and N*(1440). The total pion multiplicities and the pi(-)/pi(+) yields are calculated for selected Skyrme parameters SkP, SLy6. Ska and SIB, and also for the cases of different stiffness of symmetry energy with the parameter SLy6. Preliminary results compared with the measured data by the FOPI Collaboration favor a hard symmetry energy of the potential term proportional to (rho/rho(0))(gamma s) with gamma(s) = 2. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

Higher Moments of Net Proton Multiplicity Distributions at RHIC

200 GeV corresponding to baryon chemical potentials (mu(B)) between 200 and 20 MeV. Our measurements of the products kappa sigma(2) and S sigma, which can be related to theoretical calculations sensitive to baryon number susceptibilities and long-range correlations, are constant as functions of collision centrality. We compare these products with results from lattice QCD and various models without a critical point and study the root s(NN) dependence of kappa sigma(2). From the measurements at the three beam energies, we find no evidence for a critical point in the QCD phase diagram for mu(B) below 200 MeV.

gamma cross section in p plus p collisions at root s=200 GeV

We report on a measurement of the gamma(1S + 2S + 3S) -> e(+)e(-) cross section at midrapidity in p + p collisions at root s = 200 GeV. We find the cross section to be 114 +/- 38(stat + fit)(-24)(+23)(syst) pb. Perturbative QCD calculations at next-to-leading order in the color evaporation model are in agreement with our measurement, while calculations in the color singlet model underestimate it by 2 sigma. Our result is consistent with the trend seen in world data as a function of the center-of-mass energy of the collision and extends the availability of gamma data to RHIC energies. The dielectron continuum in the invariant-mass range near the gamma is also studied to obtain a combined yield of e(+)e(-) pairs from the sum of the Drell-Yan process and b-(b) over bar production.

Dynamics of strangeness production in heavy-ion collisions near threshold energies

Within the framework of the improved isospin-dependent quantum molecular dynamics (ImIQMD) model, the dynamics of strangeness (K-0,K-+, Lambda, and Sigma(-,0,+)) production in heavy-ion collisions near threshold energies is investigated systematically, with the strange particles considered to be produced mainly by inelastic collisions of baryon-baryon and pion-baryon. Collisions in the region of suprasaturation densities of the dense baryonic matter formed in heavy-ion collisions dominate the yields of strangeness production. Total multiplicities as functions of incident energies and collision centralities are calculated with the Skyrme parameter SLy6. The excitation function of strangeness production is analyzed and also compared with the KaoS data for K+ production in the reactions C-12 + C-12 and Au-197 + Au-197.

Importance of self-consistency in relativistic continuum random-phase approximation calculations

A fully consistent relativistic continuum random phase approximation (RCRPA) is constructed, where the contribution of the continuum spectrum to nuclear excitations is treated exactly by the single-particle Green's function technique. The full consistency of the calculations is achieved that the same effective Lagrangian is adopted for the ground state and the excited states. The negative energy states in the Dirac sea are also included in the single-particle Green's function in the no-sea approximation. The currents from the vector meson and photon exchanges and the Coulomb interaction in RCRPA are treated exactly. The spin-orbit interaction is included naturally in the relativistic frame. Numerical results of the RCRPA are checked with the constrained relativistic mean-field theory. We study the effects of the inconsistency, particularly the currents and Coulomb interaction in various collective multipole excitations.

Transport parameters in neutron stars from in-medium N N cross sections

We present a numerical study of shear viscosity and thermal conductivity of symmetric nuclear matter, pure neutron matter, and beta-stable nuclear matter, in the framework of the Brueckner theory. The calculation of in-medium cross sections and nucleon effective masses is performed with a consistent two- and three-body interaction. The investigation covers a wide baryon density range as needed in the applications to neutron stars. The results for the transport coefficients in beta-stable nuclear matter are used to make preliminary predictions on the damping time scales of nonradial modes in neutron stars.

Phenomenological analysis of the double-pion production in nucleon-nucleon collisions up to 2.2 GeV

With an effective Lagrangian approach, we analyze several NN -> NN pi pi channels by including various resonances with mass up to 1.72 GeV. For the channels with the pion pair of isospin zero, we confirm the dominance of N*(1440) -> N sigma in the near-threshold region. At higher energies and for channels with the final pion pair of isospin one, we find large contributions from N*(1440) -> Delta pi, double-Delta, Delta(1600) -> N*(1440)pi, Delta(1600) -> Delta pi and Delta(1620) -> Delta pi. There are also sizable contributions from Delta -> Delta pi, Delta -> N pi, N -> Delta pi, and nucleon pole at energies close to the threshold. We give a good reproduction to the total cross sections up to beam energies of 2.2 GeV except for the pp -> pp pi(0)pi(0) channel at energies around 1.1 GeV and our results agree with the existing data of differential cross sections of pp -> pp pi(+)p pi(-), pp -> nn pi(+)pi(+), and pp -> pp pi(0)pi(0) which are measured at CELSIUS and COSY.

Spectra of identified high-p(T) pi(+/-) and p((p)over-bar ) in Cu + Cu collisions at root s(NN)=200 GeV

We report new results on identified (anti) proton and charged pion spectra at large transverse momenta (3 < p(T) < 10 GeV/c) from Cu + Cu collisions at root s(NN) = 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider (RHIC). This study explores the system size dependence of two novel features observed at RHIC with heavy ions: the hadron suppression at high-p(T) and the anomalous baryon to meson enhancement at intermediate transverse momenta. Both phenomena could be attributed to the creation of a new form of QCD matter. The results presented here bridge the system size gap between the available pp and Au + Au data, and allow for a detailed exploration of the onset of the novel features. Comparative analysis of all available 200 GeV data indicates that the system size is a major factor determining both the magnitude of the hadron spectra suppression at large transverse momenta and the relative baryon to meson enhancement.

Role of five-quark components in radiative and strong decays of the Lambda(1405) resonance

Within an extended chiral constituent quark model, the three- and five-quark structure of the S-01 resonance Lambda(1405) is investigated. Helicity amplitudes for electromagnetic decays [Lambda(1405)->Lambda(1116)gamma, Sigma(1194)gamma] and transition amplitudes for strong decays [Lambda(1405)->Sigma(1194)pi, K- p] are derived, as well as the relevant decay widths. The experimental value for the strong decay width, Gamma(Lambda(1405)->(Sigma pi)degrees) = 50 +/- 2MeV, is well reproduced with about 50% of a five-quark admixture in the Lambda(1405). Important effects owing to the configuration mixing among Lambda P-2(1)A, Lambda P-2(8)M, and Lambda P-4(8)M are found. In addition, transitions between the three- and the five-quark components in the baryons turn out to be significant in both radiative and strong decays of the Lambda(1405) resonance.

Relativistic photoionization cross sections for atomic Mg

The photoionization cross sections of the ground level (3s(2) S-1(0)) of atomic Mg have been studied theoretically in the energy region between the Mg+(3s) and Mg+(3p) threshold using the fully relativistic R-matrix method. The positions and widths of resonances have also been obtained and compared with a recent experiment (Wehlitz et al 2007 J. Phys. B 40 2385). Excellent agreement is shown between our theoretical calculations and experimental measurements. In the present calculations, five Rydberg series of doubly excited states have been exhibited, i.e. 3pns P-1, 3pnd P-1, 3pns P-3, 3pnd D-3 and 3pnd P-3, where 3pnd P-3 are confirmed as the fifth series in contrast to the previous theoretical results.

Relativistic Continuum Random Phase Approximation and Applications II. Applications

The fully consistent relativistic continuum random phase approximation (RCRPA) has been constructed in the momentum representation in the first part of this paper. In this part we describe the numerical details for solving the Bethe-Salpeter equation. The numerical results are checked by the inverse energy weighted sum rules in the isoscalar giant monopole resonance, which are obtained from the constraint relativistic mean field theory and also calculated with the integration of the RCRPA strengths. Good agreement between the misachieved. We study the effects of the self-consistency violation, particularly the currents and Coulomb interaction to various collective multipole excitations. Using the fully consistent RCRPA method, we investigate the properties of isoscalar and isovector collective multipole excitations for some stable and exotic from light to heavy nuclei. The properties of the resonances, such as the centroid energies and strength distributions are compared with the experimental data as well as with results calculated in other models.

PROBING THE SYMMETRY ENERGY AT SUPRA-SATURATION DENSITIES FROM PION EMISSION IN HEAVY-ION COLLISIONS

Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, the emission of pion in heavy-ion collisions in the region 1 A GeV as a probe of nuclear symmetry energy at supra-saturation densities is investigated systematically, in which the pion is considered to be mainly produced by the decay of resonances Delta(1232) and N*(1440). The pi(-)/pi(+) yields are calculated for selected Skyrme parameters SkP, SLy6, Ska and SIII, and also for the cases of different stiffness of symmetry energy with the parameter SLy6. Preliminary results compared with the measured data by the FOPI collaboration favor a hard symmetry energy of the potential term proportional to (rho/rho(0))(gamma s) with gamma(s) = 2.

重子磁矩及粲重子谱研究

强子内部的有效自由度是强子物理研究的一个重要内容。本文利用含有五夸克成份的重子波函数计算了重子八重态的磁矩；利用含有偶夸克的弦模型研究单粲夸克重子谱。计算结果显示，在由轻夸克组成的重子八重态中，五夸克成分对粒子自旋磁矩有很大贡献；在含有重味夸克的重子中，将两个轻夸克近似看作偶夸克能得出合理的结果。磁矩和 衰变率的计算常常是检验重子模型是否合理的第一步。三夸克重子模型无法解释近些年来实验上发现的核子自旋丢失以及海夸克的非对称性等现象。三个价夸克与核子内的海夸克对可以形成瞬时稳定的五夸克态。邹冰松等在其模型中构造出这样一个态，它能同时给出奇异夸克对质子负的自旋贡献和正的磁矩贡献。而且该模型也能很好的解释夸克海中 被压低的实验结果。基于此模型，我们把奇异夸克的贡献推广到所有夸克贡献得出质子磁矩，然后由对称性构造其他八重态波函数并计算它们的磁矩。通过拟合实验，我们分析了重子内多夸克成分的几率，然后计算了 衰变系数以及轨道角动量对核子自旋的贡献等。含有重味夸克的重子是研究重子结构的一个非常理想的场所。近些年来，实验上发现了大量含粲夸克的重子，但是没有给出这些重子的宇称和角动量。通过分析单粲夸克重子谱，我们发现能级图中出现的劈裂可以分成宽度不同的两类。这可由引入两类偶夸克与粲夸克不同的的耦合给出解释。我们首先对含粲夸克重子按不同偶夸克进行了分类，进而给出部分粒子的宇称和角动量；然后利用A. Selem等推广的弦模型，计算了单粲夸克重子谱。 我们预测了实验上发现的一些高激发态的宇称和角动量同时给出了各种偶夸克的质量，并对其作了定性分析。我们还计算了含有粲夸克的五夸克态重子能谱。最后，对取得的结果作了讨论以及指出未来工作的方向

原子核巨共振温度变化机制

我们利用流体动力学宏观理论与HF微观理论对同位旋标量多极巨共振能量随温度的变化机制做了讨论。首先用流体动力学方法导出了同位旋标量多极巨共振能量随温度变化的一般关系式。公式表明巨共振能量随温度的变化受制于热核体积膨胀和核子平均动能增加两个因素之间的竟争，它们分别使共振能减小和增加。接着又用Skyrme-HF方法得到了核半径系数和核子平均动能随温度变化的关系式。最后得到同位旋标量多极巨共振能量随温度变化的一个简单关系式。体积膨胀和核子平均动能增加这两种因素的影响大体互相抵消，最终导致热核同位旋标量多极巨共振能量基本不随温度变化。我们用Boltzmann-Nordherin-Vlasov方程数值计算和分析了重离子反应中单极巨共振OMR的形成与衰减。为了系统地比较入射能、碰撞参数对不同反应系统GMR的形成与衰减的影响，我们计算了不同条件下不同重离子反应系统的四极矩、动能和单极矩随时间的演化。计算表明，1)GMR能量与入射能和碰撞参数无关，仅仅是核子数的函数。2) 入射能愈大GMR形成稍有提前，GMR振幅也越大但OMR振幅衰减越快GMR消亡越早。3) 碰撞参数越大GMR振幅越小GMR消亡越早。4) GMR在40fm/c左右形成，依照入射能和碰撞参数的不同在200到400fm/c后消亡，入射能愈大或碰撞参数愈大GMR消亡越早。概括地讲，GMR能量是核子数的光滑函数，与入射能或激发能无关；入射能越大GMR振幅越大，GMR形成时间稍早但衰减和消亡更快。我们用经典唯象输运模型和量子输运模型讨论了核系统扩张过程中OQR模式的密度涨落并用它们来模拟系统的集体行为。我们讨论了集体坐标Q与集体动量P的涨落随时间的演化。计算显示集体变量Q的涨落发展主要取决于通过随机驱动力引入的初始统计涨落，统计涨落与量子涨落行为相似。在核系统扩张阶段耗散与涨落机制对于动量分布的影响是重要的。量子涨落在初值中已经存在，对于低温系统，量子涨落所起的作用尤为重要，它能够缩短涨落达到特定值的临界时间，从而在动力学对称性破缺中发挥重要作用。由于量子涨落的作用，处于spinodal状态的核系统将更早地分解。我们也讨论了双核系统GDR的形成与性质，还探讨了GDR宽度随温度变化的机制。