相对论重离子碰撞中背向喷注关联的测量

发布时间：2018-03-18 05:24

本文选题：相对论　切入点：离子　出处：《中国科学技术大学》2016年博士论文　论文类型：学位论文

【摘要】：相对论重离子对撞机(RHIC)上进行的重离子碰撞实验产生了一种被称为夸克胶子等离子体(QGP)的物质形态。这种高温高密度系统中的大动量的部分子(parton)来自于核子中夸克和胶子的硬散射。部分子经过硬散射之后碎裂成的高能量的粒子束被称为喷注(jet)。部分子在穿过高温高密度介质(medium)的时候将会损失很多能量,因为可以被用来作为探针探测介质的性质。部分子穿过介质的路程越长损失的能量越大,因而被探测到的高能量的粒子通常产生于碰撞系统的边缘。所以单纯研究高能量粒子的产生对于理解QCD介质的性质和喷注介质的相互作用只能提供有限的信息。然而,喷注由于动量守恒总是背对背的产生,高能量粒子的背向(方位角差别大于π/2)喷注将会穿过整个介质并且与介质产生最大的相互作用。由高横动量粒子触发的双强子关联和多强子关联将是研究部分子在介质中的能量损失机制的有用工具。在双强子关联中,两种奇异的现象被观测到。一个是在近端(near-side方位角差别小于π/2)长程赝快度关联,另外一个是背端关联中(away-side方位角差别大于π/2)出现的双峰结构。前者被称之为“脊”(ridge),因为近端关联粒子的赝快度近似于均匀分布。后者被称之为“锥”(cone)关联,因为目前背端关联双峰结构的流行解释是马赫锥(Mach cone)。然而在这些关联测量中只有椭圆流(elliptic flow v2)的本底被扣除。更高阶流(flow harmonics),特别是三角流(triangular flow v3)的贡献被忽视。而“脊”和远端的双峰关联很有可能是由于更高阶流引起的。扣除椭圆流的背景包含两个方面,一是确定椭圆流系数的大小,二是椭圆流背景的绝对幅度。椭圆流系数可以通过独立的流的测量得到。在确定了椭圆流系数之后,人们通过假设在方位角之差等于1处(△φ=1)喷注关联的信号为零来确定椭圆流背景的绝对幅度。这种确定椭圆流背景贡献的方法被称为ZYAM方法。ZYAM方法通常会在测量中引入很大的不确定度。本论文提出了一种新的方法用于扣除喷注关联中的集体流背景。这种方法并不假设集体流的形状和幅度,而是使用已测量到的每个事例中粒子的方位角信息(data)并且可以扣除所有阶的集体流背景贡献。我们挑选在赝快度区间(0.5|η|1)相对于一个高横动量粒子有很大的反冲横动量(recoil transverse momentum, Px)的事例来增强背向喷注位于这个赝快度区间中的概率,然后在关于中心快度区对称的两个赝快度区间(一0.5|η|0和0|η|0.5)分析双强子关联。其中一个赝快度区间("close-region")离挑选反冲横动量的赝快度区间很近,另外一个赝快度区间("far-region")离挑选反冲横动量的赝快度区间很远。背向喷注由于不同的赝快度间隔对‘'close-region''的贡献大而对"far-region"的贡献小,而集体流背景对这两个关于中心快度区对称的赝快度区间的贡献一致。假设喷注关联△φ方向上的形状不依赖△η。两个赝快度区间的双强子关联之差测量了背向喷注的形状。集体流的背景被干净的扣除。论文测量了金金碰撞200GeV下背向喷注关联在不同碰撞中心度和关联粒子横动量下的宽度。背向喷注的宽度被发现随着碰撞中心度的升高而变大。背向喷注关联宽度的变大可能来源于喷注和介质的相互作用,或者是在每个事例中喷注被介质集体流弹开的平均效应,也可能是简单的nuclear KT效应。为了进一步区分不用的物理机制,论文研究了三强子关联。三强子关联也采用了类似于双强子关联的利用数据扣除各阶集体流背景的方法。基于三强子关联的结果我们讨论了可能的导致背向喷注关联展宽的物理机构。
[Abstract]:The Relativistic Heavy Ion Collider (RHIC) heavy ion collisions are produced is called a quark gluon plasma (QGP) material form. This part of large momentum of high temperature and high density in the system (Parton) hard scattering from quarks and gluons in high energy nuclear. The particle beam part after hard scattering after fragmentation into called injection (jet). In part through high temperature and high density medium (medium) will lose a lot of energy, because it can be used as a probe of nature of media. Parton medium, the longer the distance and the energy loss is high. The energy of the particles detected are usually created by the impact system of the edge. So the simple research on high energy particle QCD for understanding the nature of the medium and the jet medium interaction can only provide limited information. However, due to dynamic injection Conservation is always back-to-back production, back to the high energy particles (azimuth difference greater than PI /2) injection will be through the media and interact with the media. The biggest dihadron correlation triggered by high transverse momentum particles and the hadron correlation is a useful tool for energy loss mechanism research in medium the dihadron Association. In two, a strange phenomenon is observed. One is in the proximal (near-side azimuth difference is less than /2) long Cheng Yan rapidity correlation, the other is a back end Association (away-side azimuth difference is greater than PI /2) Shuangfeng structure. The former is called as the "ridge" (ridge), because the proximal particle Pseudorapidity is similar to the uniform distribution. The latter is called "cone" (cone), because the popular explain the back end of Shuangfeng structure is the Maher cone (Mach cone). However, in these correlation measurement Only the elliptic flow (elliptic flow V2) of the base is deducted. Higher order streams (flow harmonics), especially the river flow (triangular flow V3) contribution was ignored. "Shuangfeng Association ridge" and the distal end is likely due to the higher order streams caused. Deduction of elliptic flow background contains two that one is to determine the elliptic flow coefficient is two, the absolute magnitude of the elliptic flow background. By measuring the elliptic flow coefficient can be through independent flow. After determining the elliptic flow coefficient is equal to 1 in people by assuming the azimuth difference (delta phi =1) signal injection associated with absolute amplitude zero to determine the elliptic flow background. Determination method of elliptic flow background contribution is called ZYAM method and.ZYAM method are used in measuring the uncertainty of this. This paper proposes a new method for the deduction of collective flow in injection related background. This method does not assume the shape and amplitude of collective flow, but the use of particles has been measured in each case to the azimuth information (data) and can be deducted all order contributions. We choose the background of collective flow in Pseudorapidity intervals (0.5| |1) with a high transverse momentum with large transverse momentum recoil particle (recoil transverse momentum, Px) to enhance the case back to the injection in the Pseudorapidity probability interval, and then in two pseudo symmetrical about a central rapidity region (a region of 0.5| |0 and 0| ETA ETA |0.5) dihadron correlation analysis. One Pseudorapidity interval ("close-region") from the selection of the transverse momentum recoil Pseudorapidity interval is near another Pseudorapidity interval ("far-region") from the selection of the transverse momentum recoil Pseudorapidity interval far away. Back to the jet due to the contribution of different Pseudorapidity intervals on the "'close-region''" F and Ar-region "contribution is small, and the background of the collective flow interval two symmetrical about a central rapidity region Pseudorapidity contribution. Assuming injection direction of the shape of phi delta connection delta ETA. Do not depend on the difference of two dihadron correlation Pseudorapidity intervals measured back to the jet shape the background is set. Flow measurement of clean deduction. The Jin Jin collision 200GeV back to the injection Association in different collision centrality and particle transverse momentum under the backward jet width. The width was found with increasing collision centrality becomes larger. The interaction of backward jet width Association change can come from injection and medium, or in each case the injection was opened by collective medium average effect, it could be nuclear KT effect. In order to further distinguish the physical mechanism in use, the thesis studies three. Three hadron hadron correlation Association A method similar to the two hadron correlation is used to deduce the background of the collective flow of every order. Based on the results of the three hadron correlation, we have discussed the possible physical mechanism leading to the correlation expansion of the backjet.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O571.6

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