相对论重离子碰撞中整体喷注观测量的研究

发布时间：2018-03-29 19:34

本文选题：相对论重离子碰撞　切入点：夸克胶子等离子体　出处：《华中师范大学》2017年博士论文

【摘要】：描述强相互作用的量子色动力学理论认为,自然条件下组成物质的基本粒子夸克和胶子被禁闭在强子中,但是在极端高温高密条件下会解禁闭形成一种新的物质形态-夸克胶子等离子体(QGP)。在实验室中创造这种极端条件的手段是相对论重离子碰撞。找到夸克解禁闭的相变临界点并研究这一新物质形态的性质,一直是重离子物理理论和实验工作的热点。碰撞过程中QGP存在的时间极短,在当前实验条件下无法直接观测。经过几十年理论和实验的积累,人们发展了一系列间接研究QGP的探针,其中一个就是“喷注淬火”效应,即碰撞初期产生的快速部分子在穿越核介质时损失能量的现象,它不仅可以体现在重离子碰撞中领头强子产额的压低,还可修正整体喷注观测量。相较于领头强子,整体喷注由于携带更多物理信息是更具优势的观测量。本文中,我们系统的研究了喷注淬火效应对多个整体喷注观测量的核修正。在重离子碰撞中,初态冷核效应和末态喷注淬火效应都会对观测量造成影响。为了不受干扰的研究喷注淬火效应,我们单独计算了多个碰撞对心度区间冷核物质效应对领头强子和单举整体喷注产额的修正,结果发现从对心到边缘碰撞,冷核物质效应逐渐减弱,对我们之后研究喷注淬火效应修正的整体喷注观测量具有指导意义。紧接着,我们研究了重离子碰撞中整体喷注形状的核修正,发现核环境中整体喷注的形状与介质诱导辐射胶子的角分布直接相关,通过与CMS实验测量值对比,我们验证了多个辐射胶子的角分布模型,发现角分布倾向于dNg/dθ∝1/√θ。以此角分布模型描述介质诱导辐射的胶子,我们预测了未来超高能级重离子碰撞中整体喷注形状的核修正,以及不同尺寸重建的单举整体喷注产额的核修正,结果都表明更高能级重离子碰撞中整体喷注产额和形状的核修正与此前LHC能级中的结果接近。在同一理论框架下,我们还计算了重离子碰撞中W玻色子标记喷注产额的核修正,W玻色子标记喷注产生的微分散射截面在小横动量区域被抬升,而在大横动量区域被压低。此外,喷注的平均电荷可以完全区分夸克喷注和胶子喷注,为我们研究部分子能量损失的味道依赖提供了可能。我们首次计算了重离子碰撞中整体喷注的平均电荷。发现,相较于质子-质子碰撞,整体喷注的平均电荷值有大约20%的抬升。为了分析这一核修正的来源,我们计算了夸克喷注平均电荷的核修正因子,结果表明夸克喷注的平均电荷几乎不受核效应的影响。在我们的计算模型中,夸克喷注和胶子喷注由于各自的色因子不同而损失不同的能量,△Eq/△Eg=4/9,胶子喷注损失更多的能量导致末态观测到的同一能量区间的整体喷注中夸克喷注所占的份额增加,体现在观测量中则是使整体喷注的平均电荷值增加。因此整体喷注平均电荷的核修正仅来自于核效应对夸克和胶子相对份额的修正。我们进一步假设△Eq/△Eg=1,即夸克喷注和胶子喷注损失相同的能量,它们的相对份额不发生改变。在此假设条件下得到的喷注平均电荷的核修正验证了我们之前的结论。未来实验中精确测量重离子碰撞中整体喷注平均电荷的核修正,可以加深我们对部分子能量损失对味道的依赖的理解。
[Abstract]:Think of quantum chromodynamics theory to describe the strong interaction, under natural conditions, the material particles of quarks and gluons is confined in hadrons, but under extreme conditions of high temperature and high density will be lifted and closed to form a new state of matter quark gluon plasma (QGP). To create such extreme conditions in the laboratory means is the relativistic heavy ion collision. The critical point and find quark Deconfinement properties of this new form of matter, has been a hot topic in Heavy Ion Physics, theoretical and experimental work. Time in the collision process of QGP is very short, can not be observed directly under the present experimental conditions. After decades of experimental and theoretical accumulation. People have developed a series of indirect probe QGP research, which is a "jet quenching" effect, namely the collision energy loss produced in the early stage of the fast subsystem across the nuclear medium when the phenomenon , it can not only reflect the depression in heavy ion collisions leading hadron yields, can also be modified jet observables. Compared to the leading hadrons, jet due to carry more physical information is the measuring value of more advantages. In this paper, we systematically studied the nuclear modification of jet quenching effect on multiple the whole injection measurements. In heavy ion collisions, the initial and final state effects of cold nuclear jet quenching will have an impact on the concept of measurement. In order to study the effect of jet quenching interference, we calculated separately modified multiple collisions on heart interval cold nuclear matter effect on leading hadrons and single lift the overall yield of the jet, results from collision to the edge of the heart, cold nuclear matter effect gradually weakened, to us after the whole jet quenching effect of modified injection spray measurements have guiding significance. Then, we studied from Zi Peng Nuclear modification jet crashed into shape, that is directly related to the angular distribution and the shape of the medium in the nuclear jet induced gluon radiation, by comparing with the CMS experimental data, we verify the angular distribution of multiple gluon radiation model, found that the angular distribution tends to dNg/d / 1/ theta theta tick. This angular distribution model to describe the gluon medium induced by radiation, we predict the nuclear modification of ultra high energy heavy ion collisions in the overall level of injection in the shape of the future, and different sizes of single injection for reconstruction of the overall yield of the nuclear modification, results show that the higher level of heavy ion collision jet yield and shape the nuclear modification and after LHC levels are close to the results. In the same framework, we also calculated the nuclear modification in heavy ion collisions W boson marker injection yield, W boson marker injection produced by differential cross section of the small transverse momentum region Domain were uplifted, was down in the large transverse momentum region. In addition, the average charge injection can distinguish between quark and gluon jets, study the parton energy loss for our taste on possible. We first calculated the average charge in heavy ion collision integral injection. The results show that the phase compared with the proton proton collisions, the average overall charge injection value of about 20% uplift. In order to analyze this nuclear modified source, we calculate the nuclear modification factor quark jet average charge, the result shows that the average charge quark jet is hardly affected by the nuclear effect. In our calculation model in, quark and gluon jets due to their different color factor and the loss of different energy, Delta Eq/ and delta Eg=4/9, the energy of gluon more losses caused by quark jet injection with a total energy range observed in the final Increase the share, reflected in the observation is that the average overall charge injection increased. So the overall average injection charge of nuclear modified only from the nuclear effect to quarks and gluons. We further assume that the relative share of delta Eq/ Delta Eg=1, namely quark and gluon jets loss the same the relative share of energy, they do not change. The nuclear modification injection average charge obtained based on the assumption we show the conclusion. The accurate measurement of nuclear modification in heavy ion collisions overall average charge injection experiments in the future, can deepen our understanding of the parton energy loss of taste depends on understanding.

【学位授予单位】：华中师范大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O571.6

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