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.

8B的库仑离解和天体物理学S17因子的测量

对太阳中微子问题，即在地球上观测到的太阳中微子通量同标准太阳模型理论预言之间的巨大差异的解释，依赖于~7Be(p,γ)~8B反应在低能区的反应截面，即S_(17)因子，而目前测量结果中过大的不确定性(>20%)，使得有必要对这一因子重新给予精确的测定。作为对直接质子俘获截面测量的替代，库仓离解方法被利用以获取S_(17)因子。采用入射能量E(~8B) = 254MeV/u的放射性~8B次级束流，并利用其大接收度磁谱仪KaoS，我们在GSI进行的实验通过对反应事例的逐个鉴别和不变质量分析，得到对应于S_(17)因子的质子俘获反应~7Be(p,γ)~8B的时间反演过程~8B(p,γ)~7Be的反应总截面σ_(CD) = 287 ± 15mb，以及作为反应碎片间相对动能函数的微分反应截面(dσ_(CD))/(dE_(rel))(E_(rel))。通过对微分反应截面中各种多级跃迁成份的分离，并经由细致平衡原理，我们计算得到了S_(17)因子，并在理论计算的帮助下，将其外推到太阳能区：S_(17)(0) = 21.2 ± 0.9eV·b及S_(17)(20KeV) = 20.6 ±0.9eV·b。