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Study on the proton-induced spallation reactions and the equation of state for asymmetry nuclear matter(7)Au+Au三分裂反應的輸運理論研究(42)質(zhì)子引起的散裂反應及介質(zhì)內的核子－核子有效相互作用和兩體散射截面(33)
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李慶峰博士的博士畢業(yè)論文
題目：重離子碰撞中的同位旋及近閾K產(chǎn)生
目錄
第一章 序言
第二章 研究基礎
2.1 量子分子動(dòng)力學(xué)模型（QMD）
2.1.1 QMD理論
2.1.2 QMD輸運過(guò)程
2.1.3 QMD模型的發(fā)展
2.2 相對論Boltzmann-Uehling-Uhlenbeck (RBUU)
2.2.1 傳統BUU理論的發(fā)展歷史
2.2.2 自洽RBUU理論
2.2.3 RBUU輸運過(guò)程及與QMD模型的比較
第三章 中能重離子碰撞中的同位旋
3.1 對稱(chēng)勢
3.2 介質(zhì)中兩體彈性散射截面的同位旋依賴(lài)
3.3 同位旋相關(guān)性在QMD程序中的實(shí)現
3.4 關(guān)于同位旋問(wèn)題的一些模型計算及討論
3.4.1 對稱(chēng)勢對多重碎裂產(chǎn)物的同位旋分布影響
3.4.2 系統平衡程度探索
3.4.3 兩體截面的同位旋效應對核阻止本領(lǐng)的影響
第四章 中高能重離子碰撞中的K產(chǎn)生
4.1 K介子勢
4.2 K介子產(chǎn)生基本截面
4.3 計算結果及討論
4.3.1 SIS能區重離子碰撞的K+產(chǎn)生及集體流
4.3.2 SIS能區重離子碰撞的K－吸收對其產(chǎn)生的影響
4.4 K介子研究進(jìn)展
第五章 總結及展望
Abstract
The isospin effect and K production in intermediate and high energy Heavy Ion Collisions (HICs) are hot topics in the nuclear physics. Based on the Isospin-dependent Quantum Molecular Dyanmics (IQMD) model and self-consistent Relativistic Boltzmann-Uehling-Uhlenbeck (RBUU) model, we have studied them and obtained some interesting results.
As for the study of isospin in intermediate energy HICs, we’ve investigated how stength (CS) affects many measurable observables, such as the yield, phase-space, and isospin distributions of fragments. The aim is to find sensitive observables for strength of SP. Our results show the rapidity distribution of differential neutron-proton counting (Nnp) from more neutron-rich reactions can be favorable to extract the information of SP. In the study of isospin-dependent nucleon-nucleon elastic cross sections in nuclear medium we find the medium correction of nucleon-nucleon scattering cross sections is also isospin dependent, depends on the baryon density weakly and depends on the baryon density significantly. And based on these findings, we further study the dependence of nuclear stopping on system size, initial N/Z, SP and the medium correction of two-body cross sections. It’s found that the effect of initial N/Z ratio and isospin SP on stopping is weak, and the excitation function of stopping depends on the form of medium correction of two-body cross sections and the equation of state of nuclear matter strongly. For probing the isospin dependence of the medium correction of two-body cross sections, the results show that the behavior of the excitation function of stopping for medium size nuclear collisions can provide clearer information than that for heavier systems. We have further studied equilibration with respect to isospin degree of freedom and proposed that the neutron-proton differential rapidity distribution is a sensitive probe to the energy dependence of the degree of equilibration: there exists memory effect in multifragmentation process; the degree of equilibration at E=400A MeV is higher than that at E=100A MeV; the average N/Z ratio of IMF reduces largely as beam energy increases from 100A MeV to 400A MeV.
As for the K production in high energy HICs, we firstly study K+ production. The results show that the kaon flow is sensitive to both the kaon-nucleon sigma term (SKN) and the equation of state of nuclear matter. The collective flows of both nucleons and K+ mesons need a “soft” EoS with compressibility K»200-300 MeV, and SKN=200-400 MeV seems suitable to explain the measured K+ flow. We further find that anti-flow appears at certain large impact parameter, which seems to be more sensitive to SKN and might provide more definite information of the magnitude of SKN. The absorption effect of mesons is also studied, we find although there exists strong absorption, spectrum can still contain the messages of in nuclear medium. Our investigations show the ratio of the yield of K+ to Ｋ－ depends on the size of the nuclear systems, which is mainly caused by the absorption effect of the Ｋ－ in the nuclear medium. By detailed studies on both mean-absorptions path of the Ｋ－ in different nuclear systems and the individual effect of each of elementary production channels, we find both Ｋ－ production and Ｋ－ absorption effect depend on the size of nuclear system and the elementary production processes. It should be emphasized that the channels and play important roles in theＫ－ production.
Key words: heavy ion collisions, isospin, K production
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