基于ATLAS探测器对重味夸克偶素的产生及其在核介质中的性质的研究

发布时间：2018-03-19 17:31

  本文选题：ATLAS探测器　切入点：重离子碰撞　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：重味夸克偶素(简称夸克偶素)指有正反粲夸克或底夸克对组成的介子。本论文主要基于ATLAS探测器收集的实验数据通过双缪子衰变道对五个S波夸克偶素(J/Ψ、Ψ(2S)和γ(nS)(n= 1,2,3))在核子-核子对质心系能量为5.02 TeV的质子-质子对撞、质子-铅核对撞和铅核-铅核对撞中的产生过程进行了重建,其中粲夸克偶素根据产生来源的不同区分为:直接由部分子相互作用产生的瞬发粲夸克偶素和由6强子衰变而来的非瞬发粲夸克偶素。本论文对于5.02 TeV的质子-质子碰撞中对于不同横动量和快度区间的S波夸克偶素产生截面,以及粲夸克偶素和底夸克偶素激发态相对于基态的产额比进行了测量。由于探测器性能约束,本论文仅给出了横动量区间为8pT40 GeV和快度区间为|y|2.0的粲夸克偶素的测量结果。其中瞬发和非瞬发粲夸克偶素的截面分别与对应的理论模型预言相符合,同时粲夸克偶素激发态到基态产额比和已发表的ATLAS测量结果符合较好。底夸克偶素的测量是基于横动量区间pT40 GeV和快度区间|y|2.0。相对于粲夸克偶素,底夸克偶素具有更大的不变质量和较小的对末态缪子的Lorentz推动,因而可以将横动量测量量区间扩展到0 GeV。底夸克偶素的激发态到基态产额比在5.02 TeV质子-质子碰撞中的测量结果和7 TeV的结果类似。粲夸克偶素核底夸克偶素的测量结果都说明在质子-质子碰撞中,激发态到基态产额比相对于碰撞质心系能量的依赖较弱。夸克偶素产生在重离子碰撞中的核修正因子和双重产额比,可以通过对比其在重离子碰撞中和在质子-质子碰撞的产额得到。本论文中对于质子-铅核碰撞的研究表明,在ATLAS探测器测量的运动学区间内没有发现核效应对J/Ψ的产额有显著影响,而低横动量的γ(1S)在质子-铅核对撞的产额表现出被压制。也就是说质子-铅核碰撞对高横动量的夸克偶素表现为质子-质子碰撞的简单叠加,而同时也存在对于影响低横动量的夸克偶素产额的机制。质子-铅核对撞中夸克偶素双重产额比,即质子-铅核中的激发态到基态产额比与质子-质子中的激发态到基态产额比之比,可以给出末态相互作用效应对于基态和激发态的影响的比较。粲夸克偶素核底夸克偶素双重产额比的测量结果都预示着质子-铅核碰撞中存在着依赖于夸克偶素大小和核介质大小的末态相互作用。受限于实验精度,该结果仅有一个标准差的显著度。在质子-铅核碰撞测量结果的基础上,本论文也对铅核-铅核碰撞中的粲夸克偶素产生进行了测量。测量的运动学区间和质子-质子以及质子-银核碰撞保持一致。测量结果表明瞬时和非瞬时J/Ψ的产生在铅核-铅核碰撞中被显著压低。结合质子-铅核碰撞中的测量结果,这种压低应该全部贡献于高温高密夸克胶子等离子中所独有的"热效应"。也就说ATLAS探测器提供了一个干净的、基于粲夸克偶素来专门研究热效应的窗口。瞬时粲夸克偶素关于碰撞中心度的依赖在定性上和Debye色屏蔽效应的预言一致,但定量上还有待和模型预言进行仔细比对。而非瞬时粲夸克偶素产额的压低对研究b强子在夸克胶子等离子体的能量损失提供了一个间接的工具。铅核-铅核碰撞中的双重产额比的结果表明Ψ(2S)的产额相较于J/Ψ经历了程度更强的压低。这可能是Debye色屏蔽效应存在的另外一个信号,但是我们也不能排除这种更强的压制由冷核效应贡献的可能性。
[Abstract]:Heavy quarkonium (the quarkonium) refers to has a charm quark or bottom quark meson pairs in the thesis. The experimental data collected by ATLAS detector based on double muon decay channel of five S wave quarkonium (J/ psi, psi (2S) and gamma (n= (nS) 1,2,3)) in the nuclear energy - nuclear confrontation with sub - 5.02 TeV proton proton collisions, proton nuclear generating process of lead and lead - lead at the nuclear nuclear collisions were reconstructed, the charmonium according to different sources of distinction: direct by Parton interactions, instant charm positronium and by 6 hadronic decay from non prompt charmonium collision. This paper for 5.02 TeV proton proton in S wave quarkonium for different transverse momentum and rapidity region in cross section, and charmonium and bottomium excited state relative to the ground state yield ratio in the measurement. Because the detector performance constraints, this paper only gives the transverse momentum range of 8pT40 GeV and speed range for the measurement results of charmonium |y|2.0. The section of instant and non instant charmonium respectively with the corresponding theoretical model predictions are consistent with the charmonium excited state to ATLAS measurement the ground state yield ratio and published in good agreement with the measurements. The bottom quarkonium is transverse momentum and rapidity interval interval pT40 GeV |y|2.0. relative to the charmonium based bottomium has a constant quality and less more of the final muon Lorentz drive, which can measure the transverse momentum the amount of range extended to 0 GeV. bottomium excited state to the ground state yield ratio measurement results in proton proton collision of 5.02 TeV and 7 TeV in the similar results. The charmonium nuclear bottomium measurement results are described in the proton Proton collisions in the excited state to the ground state yield ratio relative to the weak dependence of mass system collision energy. Quarkonium nuclear modification factor in heavy ion collisions and double yield ratio, can yield by contrast in the heavy ion collisions in proton proton collisions. Research on proton nuclear lead this paper shows that the collision, in the Sports School District ATLAS detector measuring room not found significantly affected the yield of J/ is the nuclear effect, while the low transverse momentum gamma (1S) suppressed by proton nuclear collisions lead yield show. That is to say of quarkonium proton nuclear collisions lead to high transverse momentum in the performance of the simple superposition of proton proton collisions, but also has influence on low transverse momentum quarkonium production mechanism. Proton nuclear collisions lead quarkonium double yield ratio, namely the ratio of the yield of excited state to the ground state proton nuclear in the lead With the proton proton in the excited state to the ground state yield ratio, can be given the final state interaction effect on the ground and excited state. The charmonium nuclear bottomium double yield ratio measurement results indicate that there exists interaction depends on the size of the quark positronium and nuclear medium size of final proton nucleus collisions. Lead is limited by the accuracy of the experiment, the results of only one standard deviation of significant degree. Based on measurement results of proton nuclear collisions on the lead, the lead - lead nuclear charm even in nuclear collisions generate were measured. The measurement of sports school and the proton proton proton collision and silver core consistency. The measurement results show that the instantaneous and non instantaneous J/ psi production was significantly lower in the lead - lead nuclear nuclear collisions. Combined with the measurement results of proton - lead in nuclear collisions, this should all contribute to the high temperature down High density quark gluon plasma in the unique "thermal effect". It said ATLAS detector provides a clean window, I have devoted to the study of the charm quark. Based on the thermal effect on instantaneous charmonium on collision centrality in qualitative and Debye color screening effect is consistent, but quantitative also need to be carefully compared. And the model predicted and non instantaneous charmonium yield down to study B hadron provides an indirect tool of energy loss in the quark gluon plasma. Nuclear lead - lead in nuclear collisions double yield ratio (2S) results show that only the yield compared to in J/ only experienced more depression. This may be another sign of Debye color screening effect, but we can not rule out the possibility of suppressing the stronger by the cold nuclear effect contribution.

【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】：2017
【分类号】：O572.2
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本文编号：1635288