在RHIC能区质子—质子和金—金原子核对撞中重味夸克产额

发布时间：2017-12-28 19:19

本文关键词：在RHIC能区质子—质子和金—金原子核对撞中重味夸克产额　出处：《华中师范大学》2017年博士论文　论文类型：学位论文

【摘要】：相对论重离子碰撞的一个主要目的是研究在非常高的温度和能量密度下,解禁闭的夸克和胶子等离子体(QGP)的形式和性质,以及它们和硬部分子之间的相互作用。位于布鲁克海文国家实验室(BNL)的相对论重离子对撞机(RHIC)和欧洲的大型强子对撞机(LHC)的实验结果表明,这种新的物质形态可以通过超高能相对论重离子碰撞产生。但是在实验上很难直接观察这种新的物质形态,因为夸克和胶子带色荷,因此它们会禁闭在强子内部。在实验上观测到的是末态的冷却的粒子,这种末态的粒子受到冷核和热核效应的影响,所以很难从末态粒子观测早期的QGP的演化过程。重夸克被认为是研究QGP的完美探针,因为它们在重离子碰撞初期通过部分子的硬散射过程产生,而且质量很大,在RHIC能级下很难在QGP的演化中再产生。因此重夸克携带了系统的早期阶段的碰撞信息和QGP的热介质信息。在系统的演化过程中,重味夸克穿过介质并且和QGP相互作用,因此重夸克的性状中携带有QGP演化的信息,因此精确地分别测量charm夸克和bottom夸克的产额对于理解重夸克与介质的相互作用,以及介质的性质,部分子的能量损失机理是非常重要的。由于重味夸克质量(charm 和 bottom 夸克,mc≈1.3 GeV/c2 and mb≈ 4.2 GeV/c2)远高于量子色动力学QCD标度(大约200 MeV),所以重味夸克的产生过程伴随着较高的横动量转移。由于QCD的渐近自由,这个过程可以很好地用微扰QCD描述。在试验中精确的测量重味夸克的产生可以很好地检验微扰QCD计算,而且为模型计算提供较准确的参数。在2014年,STAR实验组安装了一个重味夸克劲迹探测器(HFT),这是一个新的硅探测器,具有非常好的位置分辨率用于测量衰变顶点和碰撞顶点之间的最近距离(DCA)。由于charm和bottom强子的寿命不一样,通过DCA的差异,就能够分开charm和bottom强子半轻子衰变产生的电子。半轻子衰变道可以通过测量重味介子衰变产生的电子来测量重味夸克,尽管这是一种间接测量的办法,但也是一种非常有效的测量方法。在RHIC能区下重味夸克的产生截面比较小,所以测量一直受统计量的影响。和强子衰变道相比,半轻子衰变道衰变的电子有较好的统计量。在本论文中,除非有特别说明,所有的电子包括正电子和负电子。我们最新的实验数据是在质心系200 GeV质子-质子对撞中charm和bottom强子半轻子衰变产生的电子的产额,分析结果和微扰QCD的次领头阶(FONLL)计算在误差范围内一致。电子在质子-质子对撞的产额可以作为原子核对撞电子产额的基线,来研究热部分子在高温高密的介质中的能量损失。我们测量结果表明,非光电子的核修正因子在所有的中心度区间,高横动量(4 GeV/cpr)范围有比较大的压低,且压低随着中心度的增加而不断减少,在低横动量区间核修正因子有加强,但是系统误差很大。我们分别测量了charm和bottom强子通过半轻子衰变道产生的电子在质心系200 GeV金-金对撞的产额。本次测量结果表明bottom强子半轻子衰变产生的电子的核修正因子压低比charm强子衰变产生的电子要小,这一结果被认为bottom夸克和charm夸克相比,在热部分子中损失的能量要小。
[Abstract]:The main purpose of relativistic heavy ion collisions is to study the form and properties of quark and gluon plasma (QGP) at the very high temperature and energy density, and the interaction between them and hard part molecules. Brook is located at the Brookhaven National Laboratory (BNL) of the Relativistic Heavy Ion Collider (RHIC) and Europe's Large Hadron Collider (LHC). The experimental results show that this new material can form by ultra high energy relativistic heavy ion collisions. However, it is difficult to directly observe the new form of material in the experiment because the quarks and gluons are charged with color, so they are confined within the hadron. In the experiments of the final cooling of particles, the final particles affected by cold nuclear and thermonuclear effect, so it is difficult from the evolution process of final particles in early QGP observation. Heavy quark is considered to be a perfect probe for studying QGP, because they are produced by hard scattering process of partial ions in the early stage of heavy ion collisions, and the mass is very large, so it is difficult to generate in the evolution of QGP at RHIC level. So the heavy quark carries the collision information at the early stage of the system and the hot media information of the QGP. In the evolution process of the system, through the medium and heavy quark and QGP interaction, so the characters of heavy quark carries the evolution of QGP information, so the accurate measurement of charm and bottom respectively, the quark quark yield for understanding the interaction of heavy quark and medium, and the nature of the medium, the energy loss mechanism of it is very important. Due to the heavy quark mass (charm and bottom quarks, MC = 1.3 GeV/c2 and MB = 4.2 GeV/c2) is much higher than the quantum chromodynamics QCD scale (about 200 MeV), so the process of heavy quark with high transverse momentum transfer. Due to the asymptotic freedom of QCD, this process can be well described with the perturbation of QCD. The precise measurement of the production of heavy quark in the test can well test the perturbation QCD calculation and provide more accurate parameters for the model calculation. In 2014, the STAR experimental group installed a heavy flavor quark detector (HFT), which is a new silicon detector. It has very good position resolution to measure the closest distance between the decay point and the collision vertex (DCA). Because of the different lifetime of charm and bottom hadrons, the electrons produced by the decay of the charm and bottom hadrons can be separated through the difference between the DCA and the hadrons. The semi lepton decay channel can be used to measure the heavy flavor quark by measuring the electrons generated by heavy flavor meson decay. Although this is an indirect measurement method, it is also a very effective measurement method. The cross section of the heavy quark in the RHIC energy region is smaller, so the measurement has been influenced by the statistics. Compared with the hadron decay path, the electrons in the decay of the semi lepton decay channel have a better statistic. In this paper, all electrons include positron and negative electrons unless there is a special description. Our latest experimental data is the yield of electrons generated by the half lepton decay of charm and bottom hadronic protons in the 200 GeV proton proton collision, and the analysis results are in agreement with the minor leader rank (FONLL) of perturbation QCD in the error range. The proton proton collision yield of electrons can be used as the baseline of the nuclear collision electron yield to study the energy loss of heat molecules in high temperature and dense medium. The results of our measurements show that the non electron nuclear modification factor in all of the central region of high transverse momentum (4 GeV/cpr) is lower relatively large, and depress continuously decrease with the increase of the center, in the low transverse momentum range nuclear modification factor to strengthen the system, but the error is large. We measured the amount of electrons produced by the charm and bottom hadrons through the semi - lepton decay channel in the mass of the 200 GeV gold - Gold colliding in the mass. The measurement results show that the electron correction factor of bottom hadronic decay is less than that produced by charm hadron decay. This result is considered that the energy loss of bottom quark and charm quark is smaller in the hot part molecule.
【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;O572.2

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