Cold-Nuclear-Matter Effects on Heavy-Quark Production in d+Au Collisions at root S-NN=200 GeV

The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d + Au and p + p collisions at root S-NN = 200 GeV in the transverse-momentum range 0.85 <= p(T)(e) <= 8.5 GeV/c. In central d + Au collisions, the nuclear modification factor R-dA at 1.5 < p(T) < 5 GeV/c displays evidence of enhancement of these electrons, relative to those produced in p + p collisions, and shows that the mass-dependent Cronin enhancement observed at the Relativistic Heavy Ion Collider extends to the heavy D meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-flavor mesons could contribute to the observed differences between the pi(0) and heavy-flavor-electron nuclear modification factors R-AA. DOI: 10.1103/PhysRevLett.109.242301

Investigation of the nuclear matter density distributions of the exotic 12 Be, 14 Be and 8 B nuclei by elastic proton scattering in inverse kinematics

The proton-nucleus elastic scattering at intermediate energies is a well-established method for the investigation of the nuclear matter distribution in stable nuclei and was recently applied also for the investigation of radioactive nuclei using the method of inverse kinematics. In the current experiment, the differential cross sections for proton elastic scattering on the isotopes $^{7,9,10,11,12,14}$Be and $^8$B were measured. The experiment was performed using the fragment separator at GSI, Darmstadt to produce the radioactive beams. The main part of the experimental setup was the time projection ionization chamber IKAR which was simultaneously used as hydrogen target and a detector for the recoil protons. Auxiliary detectors for projectile tracking and isotope identification were also installed. As results from the experiment, the absolute differential cross sections d$sigma$/d$t$ as a function of the four momentum transfer $t$ were obtained. In this work the differential cross sections for elastic p-$^{12}$Be, p-$^{14}$Be and p-$^{8}$B scattering at low $t$ ($t leq$~0.05~(GeV/c)$^2$) are presented. The measured cross sections were analyzed within the Glauber multiple-scattering theory using different density parameterizations, and the nuclear matter density distributions and radii of the investigated isotopes were determined. The analysis of the differential cross section for the isotope $^{14}$Be shows that a good description of the experimental data is obtained when density distributions consisting of separate core and halo components are used. The determined {it rms} matter radius is $3.11 pm 0.04 pm 0.13$~fm. In the case of the $^{12}$Be nucleus the results showed an extended matter distribution as well. For this nucleus a matter radius of $2.82 pm 0.03 pm 0.12$~fm was determined. An interesting result is that the free $^{12}$Be nucleus behaves differently from the core of $^{14}$Be and is much more extended than it. The data were also compared with theoretical densities calculated within the FMD and the few-body models. In the case of $^{14}$Be, the calculated cross sections describe the experimental data well while, in the case of $^{12}$Be there are discrepancies in the region of high momentum transfer. Preliminary experimental results for the isotope $^8$B are also presented. An extended matter distribution was obtained (though much more compact as compared to the neutron halos). A proton halo structure was observed for the first time with the proton elastic scattering method. The deduced matter radius is $2.60pm 0.02pm 0.26$~fm. The data were compared with microscopic calculations in the frame of the FMD model and reasonable agreement was observed. The results obtained in the present analysis are in most cases consistent with the previous experimental studies of the same isotopes with different experimental methods (total interaction and reaction cross section measurements, momentum distribution measurements). For future investigation of the structure of exotic nuclei a universal detector system EXL is being developed. It will be installed at the NESR at the future FAIR facility where higher intensity beams of radioactive ions are expected. The usage of storage ring techniques provides high luminosity and low background experimental conditions. Results from the feasibility studies of the EXL detector setup, performed at the present ESR storage ring, are presented.

Systematic study of the pi(-)/pi(+) ratio in heavy-ion collisions with the same neutron/proton ratio but different masses

A systematic study of the pi(-)/pi(+) ratio in heavy-ion collisions with the same neutron/proton ratio but different masses can help single out effects of the nuclear mean field on pion production. Based on simulations using the IBUU04 transport model, it is found that the pi(-)/pi(+) ratio in head-on collisions of Ca-48 + Ca-48, Sn-124 + Sn-124, and Au-197 + Au-197 at beam energies from 0.25 to 0.6 GeV/nucleon increases with increasing the system size or decreasing the beam energies. A comprehensive analysis of the dynamical isospin fractionation and the pi(-)/pi(+) ratio as well as their time evolution and spatial distributions demonstrates clearly that the pi(-)/pi(+) ratio is an effective probe of the high-density behavior of the nuclear symmetry energy.

Symmetry energy and isovector giant dipole resonance in finite nuclei

We study the relationship between the properties of the isovector giant dipole resonance of finite nuclei and the symmetry energy in the framework of the relativistic mean field theory with six different parameter sets of nonlinear effective Lagrangian. A strong linear correlation of excited energies of the dipole resonance in finite nuclei and symmetry energy at and below the saturation density is found. This linear correlation leads to the symmetry energy at the saturation density at the interval 33.0MeV <= S(po) <= 37.0 MeV. The comparison to the present experimental data in the soft dipole mode of (132) Sn constrains approximately the symmetry energy at p = 0.1 fm(-3) at the interval 21.2MeV similar to 22.5 MeV. It is proposed that a precise measurement of the soft dipole mode in neutron rich nuclei could set up an important constraint on the equation of state for asymmetric nuclear matter.

CONSISTENT THREE-BODY FORCE WITH BONN B POTENTIAL AND NEUTRON STAR STRUCTURE

Microscopic three-nucleon force consistent with the Bonn B two-nucleon potential is constructed, which includes Delta(1232), Roper, and nucleon-antinucleon excitation contributions. Recent results for the choice of the meson parameters are discussed. The forces are used in Brueckner calculations and the saturation properties of nuclear matter are determined. At the high densities,the nuclear equation of state and the symmetry energy are calculated. The corresponding neutron star mass-radius relations are presented.

中能重离子碰撞中的同位旋效应及非对称核物质的状态方程研究

本论文介绍了放射性核束物理研究的现状以及当前常用的几种同位旋相关的重离子微观输运理论，系统描述了非对称核物质的状态方程、中能重离子碰撞中的同位旋效应以及中子星的性质。基于 Hartree-Fock 理论和扩展的 Skyrme 相互作用，在核物质近似下得到了一个非相对论性的密度、温度和同位旋相关的核物质状态方程 (IEOS)。系统研究了核物质状态方程的同位旋效应。讨论了核子的平均场、核物质的不可压缩系数、核子的有效质量以及核物质临界温度的同位旋相关性，并且给出了核物质饱笔点处的饱和密度、不可压缩系数以及单核子结合能的抛物线规律。同时，探讨了对称能的温度和密度相关性，给出了零温度时对称能的解析表达式，并提出了对称能温度相关性的抛物线规律，发现对称能随着温度的升高而减小。另外，基于以上的同位旋相关的核物质状态方程，对 ALADIN's Caloric Curve 给出了一种静态解释。在传统量子分子动力学 (QMD) 模型的基础上，通过在相互作用平均场、两体碰撞、泡利阻塞、初始化以及碎片构造过程中适当地考虑同位旋自由度，得到了一个同位旋相关的 QMD 模型 (IQMD 模型)。利用IQMD模型系统研究了中能重离子碰撞中的同位旋效应。例如，中能重离子碰撞中同位旋自由度的弛豫、重离子碰撞中核子前平衡发射的同位旋效应、重离子碰撞中的集体流（包括直接流、转动流、挤出流和径向流）及其同位旋相关性、原子核多重碎裂的同位旋效应及其消失、重离子碰撞中的化学不稳定性以及中能重离子碰撞中如何选取事件的碰撞参数及其同位旋效应等。同样，在传统的 Boltzmann-Langevin 方程中适当地考虑同位旋自由度，得到了同位旋相关的Boltzmann-Langevin方程 (IBLE)，利用IBLE研究了 ~(19)Na的产生截面。另外，利用IQMD模型探讨了多重碎裂的"neck" 机制以及重离子碰撞中局域势的有限程效应。基于前面给出的非相对论的核物质状态方程，系统研究了中子星的性质，如中子星的化学组份、质量、结合能、半径、密度剖面、转动惯量及表面红移等。结果表明，使用一些常用的 Skyrme 势参数能够给出与天文学观测相一致的结果。

基于重离子输运理论对超重核合成及非对称核物质状态方程的研究

本论文基于重离子输运理论模型对当前人们感兴趣的超重核合成及非对称核物质状态方程做了研究。基于双核系统概念建立了一个描述超重核合成的理论模型。这个模型中通过求解Fokker-Planck方程来描述重离子碰撞过程的能量、角动量以及形变等的弛豫过程，从而合理地包含了重离子熔合过程中的动力学效应。在求解弹靶的质量扩散时采用了数值求解主方程的方法，避免对势能面做任何近似，因此能够充分地体现重离子熔合过程中弹靶的结构效应。本文利用这一模型计算了重离子熔合形成超重元素的最佳激发能、熔合几率、复合核的存活几率以及蒸发剩余核截面等，并给出了合成超重核的最佳弹靶组合。计算了超重核形成的最佳激发能，在符合已有最佳激发能实验数据的基础上预言了基于冷熔合反应合成114，116和118号元素的最佳激发能。计算了重离子熔合反应的熔合几率。结果表明，随着反应系统变得越来越重，重离子的熔合几率呈指数规律下降，准裂变变得越来越严重。这解释了实验上观测到的超重剩余核截面随体系的变重而急剧下降的现象。研究了重离子熔合截面的弹靶相关性。结果表明弹靶的质量非对称度越高越有利于熔合生成复合核，同时重离子熔合截面还强烈地依赖于弹靶结构。重离子的熔合过程是合成超重元素的关键因素之一，另一个影响超重核合成的因素是超重复合核的存活几率。基于统计模型，系统的研究了超重复合核存活几率的质量、能量、角动量等相关性。计算了基于冷熔合反应的蒸发剩余截面，得到的结果与实验基本符合，并预言了基于冷熔合反应生成114，116和115号元素的截面。在研究超重核蒸发剩余截面的弹靶相关性的基础上给出了合成超重核的最佳弹靶组合。计算表明，在挑选弹靶组合时使得合成的超重复合核是奇A核则会得到更高的奇数中子蒸发剩余核截面。计算给出了超重复合核的自旋布居及其对裂变位垒和鞍点态形变的依赖性。发现超重复合核的自旋布居强烈地依赖于复合核的裂变位垒，高的裂变位垒会给出宽的自旋布居；而超重复合核的自旋布居对鞍点态形变不是很敏感。另外研究了多核子转移反应合成超重元素的可能性。结果表明基于多核子转移反应合成大于108号的元素是很困难的。非对称核物质状态方程由于其对天体物理及理解奇异核结构的重要性，因此是人们长期以来一直感兴趣的研究内容，然而直到现在人们对核物质状态方程特别是高密核物质和非对称核物质状态状态方程仍了解甚少。基于Skyrme-Hartree-Fock理论以及同位旋相关的量子分子动力学（IQMD）模型研究了非对称核物质的化学不稳定性，结果表明非对称核物质可以发生化学不稳定性，且化学不稳定性发生的条件依赖于单粒子势能的密度相关形式。同时计算表明化学不稳定性是可以发生在真实的重离子碰撞过程中的，且在入射能量较高时化学不稳定性会消失。另外首次研究了高密核物质的化学不稳定性及其发生的条件。由于实验室很难达到很高密度的核物质，而中子星是由致密的极丰中子物质组成，因此提供了研究高密非对称核物质的自然实验室。基于Skyrme-Hartree-Fock理论研究了两种典型的非对称核物质状态方程（软对称势和硬对称势）对中子星中质子百分比的影响。另外研究了热中子星中质子百分比的温度相关性，发现热中子星中质子百分比随温度的升高而减小。基于IQMD模型研究了同位旋相分化现象的产生机制。通过与MSU的实验数据比较指出核物质应该有软的对称势。研究了重离子碰撞过程中的径向流现象，及其同位旋效应。计算了径向流产生的能量闭，并给出了实验上利用径向流产生的能量闭来提取非对称核物质状态方程的方法。

利用重离子碰撞探测非对称核物质状态方程

相对于非对称核物质状态方程，对称核物质的状态方程己基本确定。然而不同的微观·唯象多体方法对非对称核物质状态方程（尤其是对称能）的预言很不一致。利用动量相关的标量势与矢量势（对称势）及介质修正的核子一核子散射截面，在工Buuo4输运模型框架下我们对重粒子碰撞产生的丰中子核物质的状态方程进行了研究。我们发现在低密情况下对称能E32（p／po)，核物质同位旋依赖部分的等压不可压缩系数为K-55OMeF时能够较好地再现NSCL／MSU实验数据。在高密情况下π~-/π~+谱的横动量与动能分布，π~-谱的动能分布，π-的多重数，中快度前平衡核子发射的中一质比，中快度前平衡核子发射的同位旋非对称度，发射核子的中一质微分流，中一质微分椭圆流以及质子椭圆流是对对称能敏感的几个探针。其中对对称能最理想的探针是π-／π+谱的横动量与动能分布、中快度前平衡核子发射的同位旋非对称度以及发射核子的中一质微分流。利用这些对对称能敏感的观测量，通过与实验数据的对照我们就可以得出关于对称能的高密行为的重要信息。

Pauli blocking and medium effects in nucleon knockout reactions

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The Milky Way's Dark Matter Halo Appears To Be Lopsided

The atomic hydrogen gas (H I) disk in the outer region (beyond similar to 10 kpc from the center) of Milky Way can provide valuable information about the structure of the dark matter halo. The recent three-dimensional thickness map of the outer H I disk from the all sky 21 cm line Leiden/Argentine/Bonn survey, gives us a unique opportunity to investigate the structure of the dark matter halo of Milky Way in great detail. A striking feature of this new survey is the north-south (N-S) asymmetry in the thickness map of the atomic hydrogen gas. Assuming vertical hydrostatic equilibrium under the total potential of the Galaxy, we derive the model thickness map of the H I gas. We show that simple axisymmetric halo models, such as softened isothermal halo (producing a flat rotation curve with V-c similar to 220 km s(-1)) or any halo with density falling faster than the isothermal one, are not able to explain the observed radial variation of the gas thickness. We also show that such axisymmetric halos along with different H I velocity dispersion in the two halves, cannot explain the observed asymmetry in the thickness map. Amongst the nonaxisymmetric models, it is shown that a purely lopsided (m = 1, first harmonic) dark matter halo with reasonable H I velocity dispersion fails to explain the N-S asymmetry satisfactorily. However, we show that by superposing a second harmonic (m = 2) out of phase onto a purely lopsided halo, e. g., our best fit and more acceptable model A (with parameters epsilon(1)(h) = 0.2, epsilon(2)(h) = 0.18, and sigma(H I) = 8.5 km s(-1)) can provide an excellent fit to the observation and reproduce the N-S asymmetry naturally. The emerging picture of the asymmetric dark matter halo is supported by the. cold dark matter halos formed in the cosmological N-body simulation.

Quark distributions in nuclei and nuclear effects on nucleon structure functions

Extended quark distribution functions are presented obtained by fitting a large amount of experimental data of the l-A DIS process on the basis of an improved nuclear density model. The experimental data of l-A DIS processes with A >= 3 in the region 0.0010 <= x <= 0.9500 axe quite satisfactorily described by using the extended formulae. Our knowledge of the influence of nuclear matter on the quark distributions is deepened.

Three-body force effect on P-3 F-2 neutron superfluidity in neutron matter, neutron star matter, and neutron stars

We investigate the effect of microscopic three-body forces on the P-3 F-2 neutron superfluidity in neutron matter, beta-stable neutron star matter, and neutron stars by using the BCS theory and the Brueckner-Hartree-Fock approach. We adopt the Argonne V18 potential supplemented with a microscopic three-body force as the realistic nucleon-nucleon interaction. We have concentrated on studying the three-body force effect on the P-3 F-2 neutron pairing gap. It is found that the three-body force effect considerably enhances the P-3 F-2 neutron superfluidity in neutron star matter and neutron stars.

Effective mass of kaons in hyperon-rich matter

By including the scalar isovector meson delta, we extend the relativistic mean field model and the one-boson exchange model of changing K-meson in the framework of Schaffner's relativistic mean field model. We re-consider the coupling constants for the interactions between the meson and the baryon and the interactions of the K meson with different mesons as well in various parameter sets. Using our model, we discuss the effective masses of K mesons in the hyperon-rich nuclear matter. We find that the density modification of the K meson mass in the strange nuclear matter is smaller than that in the pure nuclear matter. The influence of the scalar isovector meson 6 on the effective mass of kaon is rather evident. But the extent of the influence is different in different parameter sets.