中高能重离子碰撞中奇异粒子产生和超核研究进展

本文概述了中高能重离子碰撞奇异粒子产生动力学机制和超核实验测量和理论研究进展。基于量子分子动力学(Lanzhou Quantum Molecular Dynamics model,LQMD)输运模型,即引入Skyrme能量密度泛函和相对论协变密度泛函描述核子和共振态动力学演化,考虑介子-核子和超子-核子相互作用势和阈能修正效应。以反应系统^(12)C+^(12)C、^(40)Ca+^(40)Ca、^(112)Sn+^(112)Sn和^(197)Au+^(197)Au为例,研究了阈能附近K介子、Kˉ介子和超子(Λ、Σ、Ξ)产生机制并分析了核介质效应和高密区域对称能对同位旋粒子比值的影响。基于量子并合方法构造超核并研究了超核形成相空间分布,给出超核形成的质量数、电荷数、动能、快度分布、集体流等信息。引入两体、三体、四体核子碰撞和核结构效应分析了重离子碰撞中预平衡结团发射机制。介绍了考虑同位旋矢量介子ρ和δ耦合相对论协变的量子分子动力学输运模型。

生育数量对女性工资收入的边际影响*——基于多值处理效应模型的实证分析

基于2016年中国家庭追踪调查数据,运用多值处理效应模型,实证分析生育数量对女性工资收入的边际影响。研究结果表明:第一,生育数量的增加会显著降低女性工资收入;第二,生育一孩对女性工资收入的负向边际影响比二孩更大;第三,生育数量对女性工资收入的边际影响存在显著的地域差异、城乡差异和产业差异,对东部地区、城市、第二产业从业女性工资收入的负向影响远高于中西部地区、农村、第三产业从业女性。基于上述研究结果,为进一步优化人口政策,提高生育水平,缓解人口老龄化压力,一是要运用育儿补贴、个税抵扣等方式,提高对进入劳动力市场的育儿女性的补助水平,减轻女性养育子女的经济负担;二是要进一步完善《劳动法》等相关法律法规,保障女性的平等就业权利,使女性不会因为生育而被迫离开劳动力市场,同时为女性维护自身合法权益提供支持;三是要充分发挥社会组织和社会企业的作用,加强育儿女性的劳动技能培训,帮助其保持一定的职业技能、在哺育期结束后可以更快地回归劳动力市场;四是在制定人口政策时应格外关注生育一孩的女性,例如延长一孩生育产假及陪产假时间,给予更高的育儿补贴和个税抵扣,以降低未生育女性的经济压力,从而提高我国一孩生育数量;五是考虑到生育对不同女性群体工资收入的影响程度存在差异,要针对不同地区、城乡和行业的女性群体制定差异化的生育保险政策。

Isospin splitting of nucleon effective mass and isospin effect in heavy-ion collisions

Two different isospin splittings of nucleon effective mass in nuclear medium as the form of mn*>mp* and mn*<mp* have been implemented in an isospin and momentum dependent transport model.Their impacts on the isospin emission in heavy-ion collisions is investigated thoroughly.It is found that the yield ratios of energetic neutrons to protons squeezed out during the compression stage of two colliding nuclides are sensitive to the isospin splitting.The elliptic flows of free nucleons are also to be promising observables for extracting the nucleon effective mass splitting.Further experimental measurements are being expected,in particular at the CSR-CEE platform in Lanzhou.Several observables are proposed for constraining the density dependence of symmetry energy,such as the transverse flow difference of neutrons and protons,double ratios of n/p and π-/π+,excitation functions of π-/π+ and K0/K+.

1-3 In-medium and Isospin Effects on Pion Production in Heavy-ion Collisions Near Threshold Energies

Properties of hadrons in nuclear medium is interest in studying the Quantum Chromodynamics (QCD) structure in dense matter, in particular related to the chiral symmetry restoration, phase-transition from quark-gluon plasma to hadrons, dynamics of hypernucleus formation, nuclear equation of state (EoS), etc. High energy heavy-ion collisions in terrestrial laboratory provide a unique possibility to study the in-medium properties of hadrons in dense nuclear matter and to extract the high-density behavior of the nuclear symmetry energy (isospin asymmetri part of EoS). The dynamics of pseudoscalar mesons in heavy-ion collisions and the in-medium properties in dense nuclear matter have been investigated with the Lanzhou quantum molecular dynamics (LQMD) transport model[1].

1-2 Nuclear Fragmentation in Low-energy Antiproton Induced Reactions

The dynamics of antiproton-nucleus collisions is complicated, which is associated with the mean-field potentials of hadrons in nuclear medium, and also with a number of reaction channels, i.e., the annihilation channels, chargeexchange reaction, elastic and inelastic collisions. Larger yields of strange particles in antiproton induced reactions are favorable to form hypernuclei in comparison to proton-nucleus and heavy-ion collisions.

1-4 A Statistical Approach to Describe Highly Excited Heavy and Superheavy Nuclei

The synthesis of very heavy (superheavy) nuclei is a very important subject in nuclear physics motivated by reaching the island of stability predicted theoretically, which has obtained much progress in experiments with fusionevaporation reaction mechanism. The existence of superheavy nucleus (SHN) (Z  106) is due to a strong shell effect against the large Coulomb repulsion. However, the shell effect will be reduced by the increasing excitation energy of the formed compound nucleus. The fusion-evaporation reaction to form superheavy compound nucleus can be understood as three stages in accordance with the evolution of two heavy colliding nuclei, namely the capture process of the colliding system to overcome Coulomb barrier, the formation of the compound nucleus to pass over inner fusion barrier, as well as the de-excitation of the thermal compound nucleus against fission[1]. The survival probability in the last stage is particularly important in the evaluation of production cross sections of heavy and superheavy nuclei.

1-4 Strangeness Production in Antiproton Induced Nuclear Reactions.

More localized energy deposition is able to be produced in antiproton-nucleus collisions in comparison withheavy-ion collisions due to annihilation reactions. Searching for the cold quark-gluon plasma (QGP) with antiprotonbeamshas been considered as a hot topic both in experiments and in theretical calculations over the past severaldecades. Strangeness production and hypernucleus formation in antiproton-induced nuclear reactions are importancein exploring the hyperon (antihyperon)-nucleon (HN) potential and the antinucleon-nucleon interaction, whichhave been hot topics in the forthcoming experiments at PANDA in Germany.

1-3 Nuclear In-medium Effects of Strange Particles in Proton-nucleus Collisions

Extraction of the in-medium properties of strange particles from heavy-ion collisions is very complicated, since he nuclear density varies in the evolution of nucleus-nucleus collisions. To avoid the uncertainties of the baryon ensities during the stage of strange particle production, one can investigate proton-nucleus collisions where the uclear density is definite around the saturation density. Dynamics of strange particles produced in the protoninduced uclear the reactions near the threshold energies has been investigated within the Lanzhou quantum olecular dynamics (LQMD) transport model. The in-medium modifications on particle production in densenuclear matter are considered through the corrections to the elementary cross sections via the effective mass and he mean-field potentials[1].