本文關(guān)鍵詞：KN勢對中能重離子碰撞中K介子產(chǎn)生影響的研究　出處：《沈陽師范大學》2017年碩士論文　論文類型：學位論文

  更多相關(guān)文章： 重離子碰撞 對稱能 集體流 KN勢

【摘要】：核物質(zhì)狀態(tài)方程(EOS)一直都是核物理領(lǐng)域一個十分重要的課題。重離子碰撞中產(chǎn)生的K介子可以作為核反應(yīng)中形成的高密核物質(zhì)的一個有效探針,結(jié)合輸運模型模擬可以提取出高密核物質(zhì)狀態(tài)方程的相關(guān)信息。目前人們對同位旋對稱(中子、質(zhì)子數(shù)目相同)核物質(zhì)的狀態(tài)方程已經(jīng)有一定的了解,認為其具有“軟”的性質(zhì),但對于同位旋不對稱的核物質(zhì)仍舊不是十分清楚。近年來隨著研究的不斷深入,同位旋非對稱核物質(zhì)的EOS漸漸引起了大家的關(guān)注,其中引起熱議的便是其最大的不確定部分,即來自于密度依賴的對稱能部分。通過對實驗數(shù)據(jù)和輸運模型的模擬相結(jié)合可以作為探究高密核物質(zhì)狀態(tài)方程的一個有效方法。本文首先對K介子以及國內(nèi)外重離子碰撞領(lǐng)域運用的輸運模型作以相關(guān)介紹,并在最近更新的極端相對論量子分子動力學(UrQMD)模型基礎(chǔ)上,以中能區(qū)(入射能量為0.6-2.0GeV/nucleon)Au+Au碰撞為例,探究了時間步長對各種觀測量(質(zhì)子以及π介子的產(chǎn)額和集體流)的影響。發(fā)現(xiàn)觀測量會不同程度的受到時間步長的影響,其對π介子相關(guān)觀察量的影響更明顯于對質(zhì)子的作用。本文進一步在UrQMD模型中引入了K介子與核子間相互作用勢(KN勢),詳細給出了KN勢推導過程以及如何應(yīng)用到現(xiàn)有模型當中。同樣以中能區(qū)Au+Au碰撞為例,研究了KN勢對K介子產(chǎn)額和直接流、橢圓流的影響。研究結(jié)果表明,KN勢使得K~+和K~0介子與核子之間存在排斥作用,從而產(chǎn)生與核子反向的直接流。當考慮KN勢后,能夠更好的再現(xiàn)K介子集體流的實驗數(shù)據(jù)。還研究發(fā)現(xiàn)了K~0/K~+產(chǎn)額比依賴于對稱能的“軟硬”,發(fā)現(xiàn)“軟”的對稱能給出的K~0/K~+產(chǎn)額比更高;入射能量越低時,K~0/K~+產(chǎn)額比對對稱能的敏感性就越強。入射能量為0.8 GeV/nucleon時,K~0/K~+產(chǎn)額比對對稱能的敏感性要高于π~-/π~+產(chǎn)額比。隨著實驗上對重離子碰撞過程中K介子相關(guān)觀察量的進一步準確測量,以及輸運模型的不斷優(yōu)化,可以在這一能量下,利用K介子對對稱能進行合理有效的約束。
[Abstract]:The state equation of state of nuclear matter (EOS) has always been a very important subject in the field of nuclear physics. K mesons generated in heavy ion collisions can be used as an effective probe for high-density nuclear matter formed in nuclear reactions. Combined with transport model simulation, we can extract relevant information of high-density nuclear matter equation of state. At present, people have known a lot about the equation of state of isospin symmetry (the same number of neutron and proton), and think it has a "soft" nature, but for isospin asymmetric nuclear matter, it is still not very clear. In recent years, with the deepening of research, the EOS of isospin asymmetric nuclear materials has attracted more and more attention. The most uncertain part is the density dependent symmetric energy part. The combination of the experimental data and the simulation of the transport model can be used as an effective method to explore the state equation of high density nuclear matter. The transport model firstly by ion collision domain of K meson at home and abroad as well as heavy as related to, and in a recent update of the relativistic quantum molecular dynamics (UrQMD) model based on the energy region (incident energy 0.6-2.0GeV/nucleon) Au+Au collision as an example, to explore the time step to measure various views (proton and pion yield and collective flow effect). It is found that the observable measurements are affected by the time step in varying degrees, and the effect on the pion correlation observation is more obvious to the protons. In this paper, we further introduce the K meson and nucleon interaction potential (KN potential) in the UrQMD model, and give the detailed derivation of the KN potential and how to apply it to the existing models. The effects of KN potential on the K meson yield, direct flow and elliptical flow are also studied with the Au+Au collision in the middle energy region as an example. The results show that the KN potential rejects the K~+ and K~0 mesons and nucleons, resulting in a direct flow against the nucleon. When the KN potential is considered, the experimental data of the K meson collective flow can be reproduced. It is also found that the K~0/K~+ yield ratio is dependent on the "soft and hard" dependence of the symmetric energy. It is found that the K~0/K~+ yield ratio of the "soft" symmetry energy is higher; the lower the incident energy is, the more sensitive the K~0/K~+ yield ratio to the symmetry energy is. The incident energy is 0.8 GeV/nucleon, the sensitivity of K~0/K~+ yield ratio is higher than that of the symmetry energy ~-/ Pi Pi + yield ratio. With the further accurate measurement of K meson related observations in heavy ion collisions and the continuous optimization of transport models, we can use the K meson to reasonably and effectively constrain the symmetry energy.
【學位授予單位】：沈陽師范大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：O571.6

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