RHIC能区铀核铀核对撞中双轻子产生

发布时间：2018-06-10 19:58

  本文选题：RHIC + 能区　； 参考：《中国科学技术大学》2016年博士论文

【摘要】：量子色动力学是用来描述夸克和胶子间强相互作用的规范场理论。格点量子色动力学预言在高温或高重子化学势的条件下会发生从强子物质到夸克胶子等离子体(QGP)的相变。坐落在美国布鲁克海文国家实验室(BNL)的相对论重离子对撞机(RHIC)是专门用于研究夸克胶子等离子体性质以及量子色动力学相图的实验装置。双轻子不参与强相互作用,并且可以在重离子对撞整个演化过程中产生,因此,双轻子的测量在研究这种高温高密物质中起着至关重要的作用。根据不同的产生机制,双轻子的不变质量谱一般被划分成三个质量区间。高质量区间(HMR, Mll MJ/ψ),双轻子主要由初始的硬过程产生,例如Drell-Yan,夸克偶素的衰变。中间质量区间(IMR, MφMllMJ/ψ),双轻子主要由夸克胶子等离子体的热辐射以及开粲的半轻子衰变产生,其中热辐射的双轻子产额可用于测量夸克胶子等离子体的温度。低质量区间(LMR, MuMφ),双轻子主要由在强子介质中矢量介子(ρ,ω,φ,等)的衰变产生,他们可用于研究介质中的手征对称性恢复。此外,ALICE合作组最近观察到在质心能量为2.76 TeV的铅核-铅核偏心对撞中,超低横动量(pT0.3 GeV/c)的前向快度J/(?)产额有非常大的增强。这部分增强有可能来自相干光产生过程。如果在偏心重离子对撞中,也可以通过相干光产生生成ρ介子,这部分ρ介子可用作一个直接测量夸克胶子等离子体性质的探针。本论文利用位于相对论重离子对撞机上的螺旋径迹探测器(STAR),首次研究了双轻子在铀核-铀核对撞中的产生。用于该分析研究的数据采集于2012年。利用时间投影室测量的电离能损以及飞行时间探测器测量的粒子速度进行正负电子的鉴别。在铀核-铀核的最小无偏对撞中(中心度：0-80%),鉴别出来的电子整体纯度可以达到95%。通过对比在最小无偏对撞中测量的STAR接收度内(pTe 0.2 GeV/c, |ηe|1, and |yee|1)的双轻子不变质量谱和不包含ρ介子贡献的强子衰变模拟(cocktail),我们发现在类ρ质量区间0.3-0.76 GeV/c2内,测量的双轻子产额比模拟的产额高2.1±0.1(stat.)±0.2(sys.)±0.3(cocktail)倍。我们还系统的测量了不同横动量以及中心度区间的双轻子不变质量谱,发现此增强因子并没有很强的中心度以及横动量依赖性。为了定量的研究这些双轻子增强,我们还测量了修正STAR接收度的双轻子增强谱(data-cocktail ).上面提到的所有双轻子增强谱都可以用一个包含ρ展宽的谱函数以及夸克胶子等离子体热辐射贡献的理论模型描述。ρ介子谱在高温高密介质中的展宽被认为和手征对称性恢复有关。进一步的分析研究表明,带电粒子密度(dNch/dy)归一的修正了STAR接收度的积分增强产额(积分区间：0.4Mee0.75 GeV/c2)有很强的中心度以及对撞能量的依赖性。中心对撞中的归一积分增强产额比偏心对撞以及低能量对撞的产额要高。最近一个理论模型指出,在质心能量为6到200 GeV区间内,dNch/dy归一的积分增强产额正比于重离子对撞中产生介质的寿命。这预示着在铀核-铀核中心对撞中产生的介质的寿命比在偏心对撞中或者低质心能量重离子对撞中产生的介质寿命长。本论文还首次测量了铀核-铀核对撞中STAR接收度内超低横动量(Pr 0.15 GeV/c)的双轻子不变质量谱。相对于强子衰变的模拟产额,偏心对撞中的双轻子产额在整个质量区间都有很大的增强。在质量区间0.4-0.76 GeV/c2和2.8-3.2 GeV/c2中,增强因子分别为16.4±1.1(stat.) ±2.6(sys.)± 4.2(cocktail), 20.4±4.2(star.)±3.0(sys.)±3.2(cocktail)。这些增强可能来自于相干光产生过程。我们还测量了铀核-铀核对撞中STAR接收度内不同质量区间的双轻子横动量谱(0.4Meκε 0.76 GeV/c2, 1.2 Meε2.67GeV/c2, and 2.8 Meε 3.2 GeV/c2),发现这些横动量谱的形状在偏心对撞中在0.1 GeV/c附近发生急剧变化。此外,本论文还报告了两种气体探测器-迷你漂移厚气体电子倍增室(mini-drift THGEM )和多气隙阻性板室(MRPC)的研制以及测试结果。THGEM用作穿越辐射探测器(TRD)的读出探测器,用来鉴别电子离子对撞机上的前向散射电子和提供额外的电离能损(dE/dx )测量,后者对小角度散射的带电粒子径迹重建非常重要。这是首次提出用THGEM作为TRD的读出探测器。宇宙线测试结果表明，，在工作电压下,THGEM的探测效率高于94%,位置分辨能达到220μm。由于THGEM具有非常好的位置分辨以及相对厚的电离区,THGEM展现出非常卓越的径迹重建能力。最后,测试结果表明THGEM增益均匀性以及稳定性也非常好。为了提高北京谱仪的粒子鉴别能力,MRPC被用来升级北京谱仪端盖飞行时间探测器(eTOF)。我们在正负电子对撞机E3束流线上用动量为600MeV/c的质子束测试了单端读出和双端读出MRPC、~在工作高压下,两种MRPC的探测效率都高于98%。单端读出MRPC的时间分辨为47 ps,但有带电粒子入射位置的依赖性。双端读出MRPC的时间分辨为40 ps,且没有带电粒子入射位置的依赖性。根据这次束流测试结果,双端读出MRPC被用于北京谱仪的eTOF升级。北京谱仪的eTOF升级已于2015年11月完成,对电子的时间分辨可达到60 ps,远好于其设计指标(80 ps)。
[Abstract]:Quantum chrodynamics is a standard field theory used to describe the strong interaction between quarks and gluons. Lattice quantum chromo dynamics predicts that the phase transition from hadron matter to quark gluon plasma (QGP) occurs under the condition of high temperature or high baryon chemical potential. The relativistic heavy ion pair located in the Brook National Laboratory (BNL) of the United States The Collider (RHIC) is an experimental device specially used to study the properties of the quark gluon plasma and the quantum chromatic phase diagram. The double lepton does not participate in the strong interaction and can be produced during the entire evolution of heavy ion collisions. Therefore, the measurement of the double lepton plays a vital role in the study of the high temperature and high density material. In the same generation mechanism, the invariant mass spectra of the dual leptons are generally divided into three mass intervals. The HMR, Mll MJ/ are mainly produced by the initial hard processes, such as the decay of Drell-Yan, quarkeven, the intermediate mass interval (IMR, M phi MllMJ/), and the dual leptons mainly by the heat radiation of the quark gluon plasma and the charm of the quark plasma. Semi lepton decay in which the double lepton yield of heat radiation can be used to measure the temperature of the quark gluon plasma. The low mass interval (LMR, MuM phi), the two leptons are mainly produced by the decay of the vector mesons (rho, Omega, phi, etc.) in the hadronic medium, and they can be used in the chiral symmetry recovery in the study medium. In addition, the ALICE cooperation group recently looked at it. It is observed that in the eccentricity of the lead core eccentricity of the centroid energy of 2.76 TeV, the forward fast J/ (?) output of the ultra low transverse momentum (pT0.3 GeV/c) is greatly enhanced. This part of the enhancement may come from the coherent light production process. If in the eccentrically heavy ion collisions, the P meson can also be generated by the coherent light. This part of the P meson can be used as a meson. A probe to directly measure the properties of the quark gluon plasma. This paper first studied the production of double leptons in uranium nuclear uranium nuclear collisions by using the spiral track detector (STAR) on the Relativistic Heavy Ion Collider. The data used in this analysis were collected in 2012. The ionization energy loss and flight measured by the time projection chamber. The particle velocity measured by the row time detector is identified by the positive and negative electrons. In the minimum unbiased collision (center degree: 0-80%) in the uranium nuclear uranium core (center degree: 0-80%), the identified electronic purity can reach the two lepton invariant mass spectra (pTe 0.2 GeV/c, pTe e|1, and |yee|1) measured by the contrast in the minimum unbiased collision. And the hadron decay simulation (cocktail), which does not contain the contribution of the P meson (cocktail), we find that the measured double lepton yield is 2.1 + 0.1 (stat.) + 0.2 (sys.) + 0.3 (cocktail) times higher than the analog output in the class Rho mass interval (stat.). We also systematically measured the two lepton invariant mass spectra of different transverse momentum and central degree, and found this The enhancement factor does not have a strong centrality and transverse momentum dependence. In order to quantify these dual lepton enhancements, we also measured the double lepton enhancement spectrum (data-cocktail) for the correction of the STAR reception. All of the two lepton enhancement spectra mentioned above can be used by a spectral function containing Rho and the heat of the quark gluon plasma. The theoretical model of the radiation contribution is described. The broadening of the P meson spectrum in high temperature and high density media is considered to be related to the chiral symmetry recovery. Further analysis shows that the integral enhancement of the charged particle density (dNch/dy) is corrected by the integral enhancement of the STAR receiver (integral interval: 0.4Mee0.75 GeV/c2) with a strong centrality and collision energy. The last theoretical model indicates that the integral enhancement of the dNch/dy return is proportional to the lifetime of the medium in the heavy ion collisions, which indicates that in the uranium nuclear uranium nuclear center, the latest theoretical model points out that in the center of mass energy is 6 to 200 GeV intervals. The lifetime of the medium produced in the collision is longer than that produced in the eccentrically collided or low centroid energy heavy ion collisions. This paper also first measured the two lepton invariant mass spectra of the ultra low transverse momentum (Pr 0.15 GeV/c) in the STAR receiving degree of uranium nuclear and uranium nuclear pair collisions. The yield of lepton is greatly enhanced in the whole mass range. In the mass interval 0.4-0.76 GeV/c2 and 2.8-3.2 GeV/c2, the enhancement factors are 16.4 + 1.1 (stat.) + 2.6 (sys.) + 4.2 (cocktail), 20.4 + 4.2 (star.) + 3 (sys.) + 3.2 (cocktail). These enhancements may come from the coherent light production process. We also measured uranium nuclear uranium nucleation The two lepton transverse momentum spectra (0.4Me kappa e 0.76 GeV/c2, 1.2 Me e 2.67GeV/c2, and 2.8 Me e 3.2 GeV/c2) in the different mass intervals in the STAR receiving degree are found. It is found that the shape of these transverse momentum spectra changes sharply near 0.1 GeV/c in the eccentricity collision. In addition, this paper also reported two gas detectors - Mini drift thick gas electrons. The development and test results of the multiplier chamber (mini-drift THGEM) and multi air gap resistive plate chamber (MRPC),.THGEM is used as a read-out detector to cross the radiation detector (TRD) to identify the forward scattering electrons on an electron ion collider and provide an additional ionization energy loss (dE/dx) measurement. The latter reconstructs charged particle tracks for small angle scattering. It is often important. This is the first time to propose a readout detector using THGEM as a TRD. The results of the cosmic ray test show that the detection efficiency of THGEM is higher than 94% under the operating voltage and the position resolution can reach 220 M. because THGEM has a very good position resolution and a relatively thick ionization area, and the THGEM shows excellent track reconstruction ability. Finally, the test is tested. The results show that the THGEM gain uniformity and stability are very good. In order to improve the particle identification ability of the Beijing spectrometer, MRPC is used to upgrade the end cover flight time detector (eTOF) of the Beijing spectrometer. We test the single end readout and double end readout MRPC with the proton beam of 600MeV/c on the E3 beam line of the positive and negative electron collider. Under high pressure, the detection efficiency of the two kinds of MRPC is higher than the time resolution of the 98%. single end readout MRPC is 47 PS, but it has the dependence on the incident position of charged particles. The time resolution of the dual end readout MRPC is 40 PS, and there is no dependence on the incident position of the charged particles. According to the results of the beam test, the dual end readout MRPC is used for the eTOF upgrade of the Beijing spectrometer. The eTOF upgrade of the Beijing spectrometer has been completed in November 2015. The time resolution of the electron can reach 60 PS, much better than its design index (80 PS).
【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】：O572.33


本文编号：2004414