高能重离子碰撞多粒子产生的热力学模型研究

评述了高能重离子碰撞中多粒子产生的热力学模型,并根据该模型的最新发展,研究了有关高能核－核碰撞中簇射粒子的赝快度分布问题． The thermodynamic models for multiparticle production in high energy heavy ion collisions are reviewed.According to the recent developments of the thermodynamic models,the pseudorapidity distributions of shower particles produced in high energy nucleus nucleus collions are investigated.     

K介子协变动力学及其准粒子模型的性质

简要综述了中高能重离子碰撞中K介子的产生及研究进展。重点介绍了K介子协变动力学模型, 并在此框架内分析了中高能重离子碰撞中K+介子以及与其伴随产生的Λ超子的集体流特征。 结果表明: 协变动力学模型能够很好地给出K+介子和Λ超子的微分直接流。 相对而言, 软势给出的集体流与实验值符合更好。同时, 通过对不同输运模型中K介子准粒子模型的基本属性进行对比分析, 明确了协变动力学模型中K介子准粒子模型的质量及能量随核物质密度的变化特征, 以及周围核子的运动对于K介子基本属性的影响。In the present paper, we briefly review the progress in the study of kaon production in heavy\|ion collisions at intermediate and high energies and introduce the covariant kaon dynamics model. The collective flows of positively charged kaon and the lambda hyperon associated produced with kaon are studied in the framework of the dynamics. It shows that the directed differential flow of K+ meson and Λ hyperon can be reasonably reproduced in the covariant kaon dynamics model. The calculated results with soft equation of nuclear matter are in better agrement with experimental data. Meawhile, a detailed comparison of the properites of different quasi\|particle models in various transport model and the influence of nucleon’s movement on the effective mass and energy of the quasi\|particle in the covariant kaon dynamics model are discussed.     

Medium effects in ΛK~+ pair production by 2.83 GeV protons on nuclei

We study ΛK~+ pair production in the interaction of protons of 2.83 GeV kinetic energy with C, Cu,Ag, and Au target nuclei in the framework of the nuclear spectral function approach for incoherent primary proton–nucleon and secondary pion–nucleon production processes, and processes associated with the creation of intermediate Σ~0K~+ pairs. The approach accounts for the initial proton and final Λ hyperon absorption, final K~+ meson distortion in nuclei, target nucleon binding, and Fermi motion, as well as nuclear mean-field potential effects on these processes.We calculate the Λ momentum dependence of the absolute ΛK~+ yield from the target nuclei considered, in the kinematical conditions of the ANKE experiment, performed at COSY, within the different scenarios for the Λ-nucleus effective scalar potential. We show that the above observable is appreciably sensitive to this potential in the low-momentum region. Therefore, direct comparison of the results of our calculations with the data from the ANKE-at-COSY experiment can help to determine the above potential at finite momenta. We also demonstrate that the two-step pion–nucleon production channels dominate in the low-momentum ΛK~+ production in the chosen kinematics and, therefore, they have to be taken into account in the analysis of these data.     

高压条件下高能重离子辐照材料研究进展

高能重离子辐照处于高压条件下材料的研究,是随着高能重离子加速器技术的快速发展而出现的一个新的研究领域, 研究结果涉及材料学、 地质学、地质年代学、核废料处理学等学科。简要介绍最近几年国内外在高能重离子辐照高压条件下材料研究领域的研究现状及已取得的结果,并对未来在兰州重离子加速器冷却储存环（HIRFL CSR）上开展相关研究工作的前景作了展望。With development of high energy heavy ion accelerator, it is possible to perform heavy ion irradiation experiments of pressurized materials in diamond anvil cells(DACs). It is a new research field. The results expected from irradiation experiments under high pressure will have impacts on several scientific fields such as materials science,geo science,geochronology,and nuclear waste storage. In this paper, some of recent works in this field are presented and reviewed. Furthermore,the research plan of materials under high pressure based on HIRFL-CSR is introduced.     

中高能核反应的新进展

简介了中高能核反应中四个基本问题方面的新进展．它们是热化与统计热平衡、气化与相变、瞬时碎裂、阈下Ｋ＋产生与Ｋ＋／π＋增强． The new development of four problems in intermediate and high energy reaction is breifly commented. The four problems are thermalization and statistically thermal equilibrium, evaporization and phase transition, simultaneous breakup and subthreshold K +production and K +/ π + enhancement.     

η production in proton-nucleus collisions near threshold

The η-meson production in proton-nucleus (pA) collisions near threshold is studied within a relativistic meson-exchange model. The primary production amplitude is presented in the distorted-wave impulse approximation for the nucleus with isospin 0 or 1 by assuming that N^*(1535) is excited via a meson exchange and then decays into η and nucleon pair(ηN). Taking ¹⁸O and ¹²C nuclei as examples, we evaluate the production cross sections as a function of the incident proton energy, and analyze the effects of nuclear medium and various meson-exchange contributions. Finally we discuss implications for further     

高能p-A碰撞的碰撞几何、能量损失和横能分布

采用一种仔细考虑了作用截面、表面弥散和形变效应的核碰撞几何,同时考虑到在每一次碰撞中领头质子损失能量,得到了高能ｐ－Ａｌ碰撞的横能分布,计算结果与２００ＧｅＶ／ｃｐ－Ａｌ、Ｃｕ及Ｕ碰撞的实验数据符合.In this paper, the nuclear collision geometry which was considered carefully in the interaction cross sections, surface effects and nuclear deformations is adopted. The energy loss of leading proton in each collision is considered. The transverse energy distributions in high energy p A collisions are obtained. The calculated results are in agreement with the experiment data of 200 GeV/ c p Al, Cu and U collisions.     

聚合物材料的快重离子辐照效应

简要介绍了快重离子辐照损伤的特点,通过与低电离辐射粒子辐照在聚合物材料中产生的效应的类比论述了快重离子辐照在聚合物材料中产生的效应及其研究现状 ,并结合快重离子辐照效应的应用展望了该领域未来的发展.The irradiation effects in polymers induced by swift heavy ions were reviewed in comparison with that induced by low ionization particles based on the characteristics of swift heavy ion irradiations. It is shown that bond breaking and cross linking, gas releasing, amorphization and carbonization of polymers depend strongly on the electronic energy loss. Besides special effects such as alkynes production, can be induced under swift heavy ion irradiation. The perspectives...     

Production of Λ-hypernuclei in A(p,K~ )ΛB reactions

The production of Λ-hypernuclei in the A(p,K )ΛB reaction is investigated in the framework of the distorted wave impulse approximation(DWIA). The total cross sections and differential cross sections for various nuclear targets are calculated with an elementary process pN→NKΛ where the additional contributions from the N*(1535) resonance and the final state interaction between p and Λ are included. The dependence of the production cross sections of Λ-hypernuclei on the phenomenological nuclear density and the nucleon number in the target, as well as the distortion effect of the incident proton and outgoing kaon, are also explored. It is shown that the distortion effect tends to decrease the cross sections by a factor of about 3—10. The production cross sections are sensitive to the adopted nuclear density.     

Antikaon production and medium effects in proton-nucleus reactions at subthreshold beam energies

The inclusive K ^--meson production in proton-nucleus collisions in the subthreshold energy regime is analyzed in the framework of an appropriate folding model for incoherent primary proton-nucleon and secondary pion-nucleon production processes, which takes properly into account the struck target nucleon momentum and removal energy distribution (nucleon spectral function), novel elementary cross-sections for proton-nucleon reaction channel close to threshold as well as nuclear mean-field potential effects on the one-step and two-step antikaon creation processes. A detailed comparison of the model calculations of the K ^- differential cross-sections for the reactions p + ⁹Be and p + ⁶³Cu at subthreshold energies with the first experimental data obtained at the ITEP proton synchrotron is given, that displays both the relative role of the primary and secondary production channels at considered incident energies and the contributions to the K ^- production coming from the use of the single-particle part as well as high-momentum-energy part of the nucleon spectral function. It is found that the pion-nucleon production channel does not dominate in the subthreshold “hard” antikaon production in p ⁹Be-, p ⁶³Cu-collisions and the main contributions to the antikaon yields here come from the direct K ^- production mechanism. The influence of the nucleon, kaon and antikaon mean-field potentials on the K ^- yield is explored. It is shown that the effect of the nucleon mean-field is of importance in explaining the considered experimental data on “hard” antikaon production, whereas the K ⁺ and K ^- optical potentials play a minor role. The sensitivity of the subthreshold “soft” antikaon production in p ⁹Be-, p ¹²C-reactions to the nucleon, kaon and antikaon mean fields is studied. It is demonstrated that, contrary to the case of “hard” antikaon production, the K ^- potential has a very strong effect on the K ^- yield, which is greater than that from nucleon effective potential. Received: 20 July 2000 / Accepted: 4 December 2000     

Subthreshold and near threshold K+ meson photoproduction\newline on nuclei

The inclusive K⁺ meson production in photon–induced reactions in the near threshold and subthreshold energy regimes is analyzed with respect to the one–step (γN→K ⁺ Y, Y=Λ,Σ) incoherent production processes on the basis of an appropriate new folding model, which takes properly into account the struck target nucleon removal energy and internal momentum distribution (nucleon spectral function), extracted from recent quasielastic electron scattering experiments and from many–body calculations with realistic models of the NN interaction. Simple parametrizations for the total and differential cross sections of the K⁺ production in photon–nucleon collisions are presented. Comparison of the model calculations of the K⁺ differential cross sections for the reaction γ+C¹² in the threshold region with the existing experimental data is given, that displays the contributions to the K⁺ production at considered incident energies coming from the use of the single–particle part as well as high momentum and high removal energy part of the nucleon spectral function. Detailed predictions for the K⁺ total and differential cross sections from γH², γC¹² and γPb²⁰⁸ reactions at subthreshold and near threshold energies are provided. The influence of the uncertainties in the elementary K⁺ production cross sections on the K⁺ yield is explored. Received: 12 April 1999 / Revised version: 11 September 1999     

基于Pluto事件产生器对兰州强子物理谱仪上主要反应道的模拟研究

为了在 GeV 能区开展核子核子相互作用中强子的产生和衰变的实验研究, 将在 HIRFL CSR 主环上建造一台兰州强子物理谱仪（HPLUS）。 首先结合 HPLUS 的初步构型阐明了针对不同极角区域的粒子鉴别方法, 接着介绍了在蒙特卡罗模拟中使用的 Pluto 事件产生器, 并针对 HPLUS上主要的反应道模拟研究了: Pluto 产生的质子质子弹性散射的角分布和实验数据的符合程度; 在产生 K 介子的反应道中, HPLUS 前角区对 K 介子的接收度; 强子衰变产生光子的最大能量和两个光子的最小夹角随极角区域的变化情况; 不同的重建方法对核子激发态质量谱形状的影响。以上研究说明了 Pluto 事件产生器可以满足 HPLUS 模拟的需要。 Hadron Physics Lanzhou Spectrometer (HPLUS) is designed for the study of hadron production and decay from nucleon nucleon interaction in the GeV region. The current formation of HPLUS and the particle identification methodsfor three polar angle regions are discussed. The Pluto event generator is applied to simulate the primary reactions on HPLUS, concerning four issues as followed: the agreement on pp elastic scattering angular distribution between Pluto samples and experimental data; the acceptance of charged K mesons in the strangeness production channels for the forward region of HPLUS; thedependence of the maximum energy of photons and the minimum vertexangle of two photons on the polar angle; the influence on the mass spectrum of excited states of nucleon with large resonant width from different reconstruction methods. It is proved that the Pluto event generator satisfies the requirements of Monte Carlo simulation for HPLUS.     

Fireball production in a quark-gluon plasma and the equilibrium of strange quarks

We study the quark-gluon plasma produced in nucleus-nucleus collisions where the laboratory kinetic energy goes from 4 to 25 GeV/ nucleon. The strange quark production is analyzed in detail and we look at the possibility for the plasma to lose energy by fireball production. Such fireballs are created inside the plasma via the dominent two-gluon fusion mechanism. Our results disagree with those of Biró and Zimányi concerning the equilibrium of the strange quark population. A prediction is made for the 15 GeV/nucleon BNL sulfur beam and for uranium-uranium collisions at 25 GeV/nucleon. In the most energetic case of uranium we obtain a saturation ratio of no more than 25%. On the other hand, a low amount of energy carried by the fireballs leads to an important increase of the ratio \({{N_s } \mathord{\left/ {\vphantom {{N_s } {N_{\bar q} }}} \right. \kern-0em} {N_{\bar q} }}\) . Using reasonable values for the parameters, we find that this ratio may reach a value of 3.5 in the most favorable case of uranium.     

电子-离子对撞机上开展核子及其激发态研究的建议

核子及其激发态性质研究一直是中高能核物理的一个重要研究领域。然而,到目前为止,对核子及其激发态内部结构的了解还处在初级阶段。首先介绍了核子及其激发态研究现状,指出了三夸克模型在描述核子特别是核子激发态内部结构方面存在很大的缺陷。为解决传统三夸克模型的不足,有一种新的观点认为虽然独立的五夸克态不存在,但是核子及其共振态中存在可观的五夸克激发。这种五夸克图像提供了一个描述核子内部结构的新见解,给出了与经典三夸克图像相当不同的核子激发态谱预言,还有待实验检验。目前国内外正在论证的电子–离子对撞机(EIC)将是研究核子结构下一代最重要的加速器装置,被视为"超级电子显微镜"。由于EIC有较高的能量和亮度,特别是低本底等优势,可以开展核子及其激发态性质的研究以及新强子态研究。     

Dissipation,mass exchange and the microscopic time scale of heavy-ion collisions

The time scale provided by the nucleon exchange mechanism in heavy-ion reactions is employed to study kinetic energy damping. The experimental kinetic energy lost per nucleon exchanged in Kr- and Xe-induced reactions is observed to decrease linearly with the total kinetic energy loss. These results, which are consistent with energy dissipation and nucleon exchange occuring on a similar time scale, are compared with the predictions of a one-body dissipation mechanism and a diffusion model.     

THE PROPERTIES OF NUCLEAR MATTER AT LOW TEMPERATURE IN A POSSIBLE QUARK MECHANISM

In this paper,the nucleon is described by the MIT bag model,and the internal quark motion in the nucleon is modified by the scalar and vector meson fields.The Fermi motion of nucleon in nuclear matter is considered.The changes for intrinsic properties of nucleon in nuclear matter at different temperature are calculated as a function of the density.The binding energy per nucleon for different temperature is given.     

A discrepancy between measured and calculated cosmic-ray spectra in the atmosphere

The flux of nucleons, pions, and muons in the energy range 1–1000 GeV and in atmospheric altitudes of 0–48 km has been calculated to a high degree of accuracy and without gross simplifications. Thus a discrepancy indicated already in 1964 byBrooke, Hayman, Kamiya andWolfendale has been firmly established. The discrepancy means, that it has proved impossible to derive the measured nucleon and muon spectra near sea-level from the measured primary nucleon spectrum unless the primary spectrum is reduced by a factor of about 2.5 or the high-energy collision models commonly used are changed. The latter would mean that the fraction of energy lost by the nucleon in a collision is passed over to the muon component to a minor extent than so far accepted, and this may be achieved in two ways: either the ratio of collision energy passed on to the electron-photon component to the energy passed on to the pion-muon component is increased in favour of the former, or about 10–20% of the collision energy are passed on to unspecified particles which do not contribute appreciably to the hard and weak components of cosmic rays. — The possibility is discussed that the missing fraction of 10–20% is spent in production of baryonantibaryon pairs.