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.

Can the nuclear symmetry potential at supra-saturation densities be negative?

In the framework of an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, for the central Au-197 + Au-197 reaction at an incident beam energy of 400 MeV/nucleon, the effect of nuclear symmetry potential at supra-saturation densities on the preequilibrium clusters emission is studied. It is found that for the positive symmetry potential at supra-saturation densities the neutron-to-proton ratio of lighter clusters with mass number A less than or similar to 3 [(n/p)(A less than or similar to 3)] is larger than that of the heavier clusters with mass number A > 3 [(n/p)(A>3)], whereas for the negative symmetry potential at supra-saturation densities the (n/p)(A less than or similar to 3) is smaller than the (n/p)(A>3). This may be considered as a probe of the negative symmetry potential at supra-saturation densities.

Medium effects on pi(-)/pi(+) in heavy-ion collisions at intermediate energies

Based on the isospin-dependent transport model IBUU and on the scaling model according to nucleon effective mass, effects of elastic and inelastic NN scattering cross-sections on pi(-)/pi(+) in the neutron-rich reaction Ca-48 + Ca-48 at a beam energy of 400MeV/nucleon are studied. It is found that cross-section effects of both NN elastic and inelastic scatterings affect Delta(1232), pi(-) and pi(+) productions as well as the value of pi(-)/pi(+).

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.

中能重离子碰撞中激发热核性质同位旋效应的实验研究

中能重离子碰撞中的核反应机制及其形成的高激发热核的性质是中能重离子物理研究的重要领域，而高激发热核性质的同位旋效应研究是这一领域的热点之一。选取了具有不同N亿比的反应体系以研究激发热核性质的同位旋效应。本论文涉及的反应系统三对共六个反应体系：55MeV／u~(40)Ar+~(58.64)Ni、30MeV/u~(40)Ar+~(112,124)Sn、35Mev／u~(36)Ar+~(112,124)Sn，这六个反应体系的N／z比分别为1.13，1.26、1.24，1.41、1.18，1.35。分别从带电粒子多重性、相对态布居核温度、关联函数等角度研究了这三对反应体系高激发热核性质的同位旋效应。在55MeV／u 40Ar+58,64Ni核反应中，用兰州4π带电粒子探测器阵列测量带电粒子多重性，研究了He和中等质量碎片的产额与反应系统的同位旋的关系，以及这种同位旋效应与反应系统的碰撞参数（即碰撞的激烈程度）、系统的激发能的变化关系。对两个反应系统，观察到带电粒子多重性中He的比分随带电粒子多重性的增加而增大，带电粒子多重性中IMF的比分随带电粒子多重性的增加而先增大，后减小的规律。两个反应系统虽然具有相同的核电荷数，但轻粒子He和中等质量碎片在多重性中的比分有明显的同位旋相关性。在30Mev／u40Sn、35MeV/u~(40)Ar~(112，124)Sn、35Mev／u 36Ar＋112,124Sn反应中用13单元望远镜探测器阵列测量了小角关联粒子。由价a关联函数提取了30Mev／u 40Ar＋112，12Sn反应系统中激发热核的态布居核温。对于不同同位旋反应系统舜UAr＋112Sn和4VAr+124Sn，提取的相对杰布居核温度分别是4.18+0.28/0.21MEV和4.10士0.22/0.20MeV；考察态布居核温度和粒子能量的关薰时，观察到两个系统的发射温度均随着粒子能量的增加而降低，缺中子系统40Ar＋l12Sn中由低能时的5.13士.30/0.26MEV降低到高能时的3.87士0.37/0.29MeV，丰中子系统40Ar＋124Sn中由低能时的5．39士0.30/0.26MeV降低到高能时的3．32士MeV。讨论了这种布居态核温度的同位旋相关性。在35Mev／u 36Ar＋112，124Sn反应中提取了洲F（3‘25）的约化速度关联函数。相对丰中子36Ar＋124Sn系统的IMF关联函数在小约化速度处反关联程度更强，表明36Ai＋124Sn系统的发射IMF的平均时间更短。用MENEKA程序提取了两个系统IMF的平均发射时间，36Ai＋112sn反应中IMF的发射时间约为150fm/c，而36Ar十124Sn反应IME的发射时间稍短，约为120fm／c。以关联IMF的单核子总能量／动量为窗条件，发现低能IMF关联函数几乎没有差别，而高能IMF关联函数在小约化速度处的差别更为明显，表明两个系统IMF关联函数的同位旋效应可能来自于IMF的早期发射。为了得到进一步的信息，我们提取了高动量窗条件下的IMF发射时间，它们比平均发射时间短，36Ar＋112Sn反应中高能IMF的发射时间约为100蒯c，而36Ai＋124Sn反应中IMF的发射时间则更短，约为50fm/c。

Possible probe on the momentum dependent interaction in the equation of state of nuclear matter

The effects of momentum dependent interaction on the kinetic energy spectrum of the neutron-proton ratio r(b)(E-k) in the equation of state of nuclear matter was investigated. We found that the kinetic energy spectrum of the neutron-proton ratio r(b)(E-k) depends sensitively on the momentum dependent interaction and weakly on the in-medium nucleon-nucleon cross section and symmetry potential so that the r(b) (E-k) is a sensitive physical probe for extracting the information of momentum dependent interaction in the heavy ion collisions. At the same time, the comparing investigate between r(b)(E-k) for the neutron-rich collision system and the same mass stable collision system gives a important judgment for extracting the information of momentum dependent interaction in the heavy ion collisions.

核物质状态方程中动量相关作用可能的探针；Possible probe on the momentum dependent interaction in the equation of state of nuclear matter

研究了动量相关作用对于中子-质子比动能谱rb(Ek)的效应,发现rb(Ek)灵敏的依赖于动量相关作用而弱的依赖于介质中核子-核子碰撞截面和对称势.因此rb(Ek)是提取重离子碰撞中动量相关作用信息的可能探针.同时,对于丰中子弹核和相同质量稳定弹核在相同入射道条件下,丰中子碰撞系统明显加强了动量相关作用对rb(Ek)的效应.故两个碰撞系统rb(Ek)结果的比较为在重离子碰撞中提取动量相关作用的知识提供了另一个重要的判据。

Finding a Probe for Extracting Information on the Momentum Dependent-Interaction in Heavy Ion Collisions

The effect of momentum-dependent interaction on the kinetic energy spectrum of the neutron-proton ratio. <(n/p)(gas)>(b)(E-k) for Zn-64 + Zn-64 is studied. It is found that. <(n/p)(gas)>(b)(E-k) sensitively depends on the momentum-dependent interaction and weakly on the in- medium nucleon- nucleon cross section and symmetry potential. Therefore <(n/p)(gas)>(b)(E-k) is a possible probe for extracting information on the momentum-dependent interaction in heavy ion collisions.