【作者】 王瑞芹；

【导师】 梁作堂； 邵凤兰；

【作者基本信息】 山东大学 ， 理论物理， 2014， 博士

【摘要】 对高能反应过程中强子化机制的研究一直是高能物理研究的一个重要且具有挑战性的课题。由于支配强子化的非微扰量子色动力学(Non-Perturbati ve Quantum ChromoDynamics)远未解决,至今人们仍然主要利用与实验相结合的唯象方法,通过研究一些对强子化机制敏感的可观测量来探索解禁闭的部分子物质的强子化机制。强子产额关联,主要指不同种类强子的产额比以及这些强子产额比之间的内在关系,是一类能够有效揭示强子化机制的可观测量。早在上个世纪70年代,人们就利用强子产额关联来研究e++e-湮灭、p+p、π+p等基本粒子反应中的强子化机制问题。近年来,对强子产额关联的研究被广泛地拓展到高能重离子碰撞中来探索高能核核反应中的强子化机制问题。众所周知,夸克组合机制是高能重离子碰撞早期产生的热密部分子物质强子化机制的有力候选者,它在重离子碰撞中的有效性是碰撞早期有解禁闭的夸克胶子等离子体(Quark Gluon Plasma)形成的一个信号。因此,检验夸克组合机制在重离子碰撞中是否适用不仅可以促进人们更好地理解高能反应中的强子化机制问题,还可以帮助人们寻找核核反应中解禁闭发生的临界碰撞能量点,完善QCD相图结构。研究强子产额关联恰恰提供了检验夸克组合机制适用性、探索高能反应强子化机制的有效途径。欧洲大型强子对撞机(Large Hadron Collider)实验和美国布鲁克海文国家实验室的相对论重离子对撞机(Relativistic Heavy Ion Collider)实验对质心系碰撞能量从几个GeV到几个TeV的重离子对撞中产生的各种强子产额关联量进行了精细的测量,积累了大量的实验数据。超级质子同步加速器(Super Proton Synchrotron)实验中的NA4、NA62、CBM等实验组测量了打靶能量20-158AGeV的Pb+Pb实验中的各种强子产额关联。交变梯度同步加速器(Alternating Gradient Synchrotron)实验提供了打靶能量从几个AGeV到十几AGeV的重离子打靶实验中产生的各种强子产额关联量数据。到目前为止,实验上已经积累了海量的有关不同碰撞能量、不同碰撞核反应、不同运动学区间上的强子产额关联的数据。这些实验数据为检验夸克组合机制在重离子碰撞中的适用性提供了必要的前提条件。通过比较组合类模型的理论计算结果与实验数据,人们可以判断各种组合模型是否有效。不同的组合模型,像ALCOR模型、夸克重组合模型、部分子融合模型等等都对强子产额关联做了大量的研究,定量地解释了实验上观测到的很多强子产额关联现象。但是,不同的组合模型采用了不同的假设和近似条件。研究清楚用不同的组合模型得出的结果是否依赖于具体的模型,在多大程度上依赖这些模型,以及得出的理论结果依赖哪些假设和近似条件对于判断夸克组合机制的有效性是非常重要的。针对这一目标,本论文对夸克组合机制下各种强子的产额关联做一系统研究。在夸克组合图像下,我们从一个一般的夸克反夸克系统出发,在尽可能不依赖于具体组合模型的情况下,解析地推导出各种强子的产额表达式,进而研究各种强子的产额关联。本论文的主要研究内容和结论总结如下：(一)从夸克组合机制的一般思想出发,在因子化假设条件下,即在夸克组合函数(也称为夸克组合的内核函数)的味道动量因子化假设和归一化的夸克联合分布函数的味道无关假设条件下,解析地推导出各种直生的轻强子和奇异强子的产额公式,并计入短寿命共振态粒子衰变,得到各种末态强子的产额表达式。这些强子产额除依赖总介子平均产额<NM>、总重子平均产额<NB>和总反重子平均产额<NB>外,只依赖于几个熟知的参数：具有相同夸克组分的矢量介子与赝标量介子比Rv/p、具有相同夸克组分的八重态重子与十重态重子比RO/D、反夸克的奇异性抑制因子λ和夸克的有效奇异性抑制因子λ。。将Rv/P和Ro/D分别取为RV/PP=3,RO/D=2时,各种强子产额除依赖(NM)、<NB>和<NB>)外,只依赖于λ和λ。。当不考虑净夸克的影响时,λ=λ。,这些强子产额公式可进一步简化并存在一系列简单的关系。(二)从因子化假设条件下推导出的强子产额公式出发,系统分析各类强子产额关联。首先,讨论在极端高能区净夸克的影响可以忽略时,有λ=λq成立,得出许多不依赖任何参数、或仅依赖λ、或依赖λ和(NB>/<NM>的结果,并与LHC能区√s=2.76TeV的Pb+Pb碰撞中中间快度区的实验数据进行比较。然后,考虑净夸克的影响,得到仅依赖于λ和λq的不同重子或不同反重子之间的产额比,依赖λ、λq和<NB>/<NM>的重子或反重子与介子的产额比,并将这些结果与RHIC能区√s=200,130,62.4GeV的Au+Au对撞和SPS能区Ebeam=158,80,40,30AGeV的Pb+Pb打靶实验数据进行比较。最后,考虑到重子和反重子受共振态粒子衰变的污染较小,能够更为干净地揭示强子化机制,我们从三个方面对各种重子反重子的味道关联进行系统的研究。第一方面是各种反重子重子比与K介子比值之间的关系。在夸克组合图像下,采用上面提到的因子化假设条件,推导出各种反重子重子比,如(Np)/(Np)、(NA)/(NA)、(Ng+)/(Ng-)、(NΩ+)/(NΩ-)与(NK-)、(NK+)之间有解析的函数关系式。这些函数关系式只与奇异性抑制因子λ有关,而且对λ的取值并不敏感。第二方面是参数无关的强子产额比恒等式。我们定义了强子产额关联量发现在夸克组合图像下有A=B=1和dAΞ=dpΩ成立。另外,我们还研究了一些混合的强子产额比,发现有成立。组合机制下得到的这些理论结果都与LHC.RHIC.SPS和AGS能区现有的实验数据进行了系统的比较。第三方面在忽略夸克整体味道补偿与考虑夸克整体味道补偿两种情况下,计算了各种重子反重子的味道关联因子,给出一些清晰的预言,等待实验的进一步检验。这些系统研究表明：组合机制下得出的有关轻强子和奇异强子产额关联的理论结果与LHC能区(?)s=2.76TeV.RHIC能区√s=200,130,62.4,39,19.6,11.5GeV和SPS能区Ebeam=158,80,40,30AGeV的实验数据符合得很好,这为夸克组合的强子化机制在这些能区的有效性提供了重要的证据。组合机制下得到的理论结果与较低的RHIC(?)s=7.7GeV.SPS Ebeam=20AGeV和AGS Ebeam=14.6,11.7,8AGeV的实验数据有所偏离,特别是在AGS能区偏离比较明显,这说明夸克组合机制在这些低能区可能已经失效。(三)ALICE实验组最新发表了一些关于LHC能区重味粲强子的实验数据,我们将夸克组合机制下得到的SU(3)强子的产额公式进行拓展,将单粲强子包括进来,研究各种单粲强子的产额关联,得出不同种类的单粲强子产额之间存在一系列简单的关系,还发现不同的单粲介子产额比能够揭示粲夸克强子化的不同性质,单粲介子产额比的横动量依赖还可以有效地反映粲夸克强子化的动力学信息。本论文的研究结果表明：在夸克组合机制的一般思想下,采用因子化假设条件之后,各种轻强子、奇异强子、单粲强子的产额之间展示出一系列简单的关联。这些强子产额之间的关联不依赖于具体的组合模型,不依赖于夸克联合分布函数和夸克组合函数的具体形式,是夸克组合图像下的一般结果。只要夸克组合机制有效,采用的因子化假设条件成立,这些强子产额关联就是成立的。因此,它们为检验夸克组合机制的适用性提供了有效的途径。组合机制下得到的这些强子产额关联特征与较高能量,像LHC、高的RHIC和SPS能区的实验数据符合得很好,表明夸克组合的强子化机制在这些反应能量下是有效的,进一步支持解禁闭的QGP物质在这些能量下已经形成的结论。但是,组合机制下的强子产额关联特征与低能区实验数据特别是AGS能区实验数据有较大的偏差,表明夸克组合机制在这些低能区反应中已经失效,进而暗示我们QGP物质在这么低的重离子碰撞反应中可能没有形成。更多还原

【Abstract】 The study of the hadronization mechanisms of high energy reactions is always an important but challenging issue in high energy physics. So far, researchers still in-vestigate indirectly the hadronization mechanisms of the deconfined partonic matter mainly by studying some hadronic observables sensitive to the hadronization mecha-nisms with phenomenological methods, since the Non-Perturbative Quantum Chromo-Dynamics (QCD) has difficulties in dealing with it directly. Hadron yield correlations, measured by the ratios of the average yields of different hadrons and the relationships of such yield ratios, are one kind of characteristic properties of hadronization mecha-nisms. They were therefore considered as good probes for the hadronization mechanism in e++e-annihilations and p+p, π+p reactions already in the1970s. Recently, many people extend the study of hadron yield correlations to high energy heavy ion collisions. As is well known, the quark combination mechanism is a powerful candidate for deal-ing with the hadronization of the partonic matter created at the early stage of heavy ion collisions. Testing the quark combination in heavy ion collisions is interesting be-cause whether the combination mechanism works might be considered as one of the signatures for the formation of the bulk color-deconfined quark matter system before the hadronization takes place. Besides, it can set lights to the search for the onset of deconfinement in nucleus-nucleus collisions and the further comprehension of the QCD phase diagram.Experimental data on hadron yield correlations are available from the BNL Rela-tivistic Heavy Ion Collider (RHIC), from relatively low energy collisions such as those obtained by NA49, NA61, and CBM Collaborations at the CERN Super Proton Syn-chrotron (SPS), and more recently from the very high energy reactions at the CERN Large Hadron Collider (LHC). So far, lots of experimental data at different collision en-ergies with different nuclei and in different kinematic regions have been accumulated. These data provide opportunities for different combination models to test the quark combination mechanism in heavy ion collisions.One can justify the quark combination mechanism by comparing the results calcu-lated by combination models with the experimental data. Different combination models, such as ALCOR model, quark (re-)combination or coalescence models have extensively studied hadron yield correlations and explained many observed interesting phenomena. However, different models use different assumptions and/or approximations. It is impor-tant to see whether, if so, to what extent, the theoretical results depend on the particular assumptions and/or approximations used in obtaining these results. For this purpose, we systematically investigate hadron yield correlations in the framework of the quark combination. We will start the study by considering the general case of the combination of quarks and antiquarks in a system from the basic ideas of the combination mecha-nism. We will make the study as independent of the particular models as possible but present the assumptions and/or approximations explicitly whenever necessary. We first deduce the general formalism of the yields of various hadrons and then systematically investigate different kinds of hadron yield correlations.The outline of the contents and conclusions of this thesis is as follows:(1) We deduce the general formalism of the yields of different hadrons in the frame-work of the quark combination. Adopting the factorization assumption, i.e., the assump-tion of the factorization of flavor and momentum dependences of quark combination functions (kernel functions) and the assumption of the flavor independence of the nor-malized quark joint momentum distributions, we analytically deduce the formulae of different directly produced light and strange hadron yields in the quark combination mechanism. Adding the decay contributions from resonances, the formulae of different final state hadron yields are obtained. Besides the total average yield of mesons (NM), the total average yield of baryons (NB) and that of antibaryons{NB), these hadron yields only depend on several familiar parameters:the ratio of the Jp=1-vector mesons to the Jp=0-pseudoscalar mesons of the same flavor composition RV/p, the ratio of the Jp=(1/2)+octet to the Jp=(3/2)+decuplet baryons of the same flavor composition Ro/d, the strangeness suppression factor for antiquarks A, and the effective strangeness suppression factor for quarks λq. Especially, when RV/P=3and Ro/D=2are taken, these hadron yields only depend on λ and λq, besides (NM),(NB) and (NR). If the influence of the net quarks can be ignored, we have λ=λq and the further simpler hadron yield formulae can be obtained.(II) With the above deduced hadron yield formulae, we further study different kinds of hadron yield correlations. Firstly, we consider ultra high energy collisions where the net quark influence can be ignored. In this case, λ=λq and many yield corre-lation results independent of any parameters or only depending on A or depending on λ and (NB)/(NM) are obtained and compared with the experimental data from LHC (?)s=2.76TeV Pb+Pb collisions. Then, including net quarks, we get the yield ratios between different baryons or antibaryons depending only on λ and λq, the yield ratios between baryons or antibaryons and mesons related with λ, λq and (NB)/(NM) and compare these results with the data from RHIC (?)s=200,130,62.4GeV Au+Au collisions and SPS Ebeam=158,80,40,30AGeV Pb+Pb collisions. Finally, we systematically study the baryon-antibaryon flavor correlations from three aspects since baryons and antibaryons suffer less decay contaminations from resonances and can probe the hadronization mechanism more clearly. One is the relationships between different species of antibaryon-to-baryon ratios and (NK-)/(NK+). In the quark com-bination, we get that different antibaryon-to-baryon ratios, e.g.,(Np)/(NP),(NA)/(NA),(N(?)+)/(N(?)-) and (NΩ+)/(NΩ-) relate with (NK-)/(NK+) by λ, but not sensitive to the values of λ. Two is several interesting regularities independent of any parame-ters. We define the following hadron yield correlation quantities In the quark combination, A=B=1and d∧≡=dpΩ. In addition, we discuss the mixed ratios and find that All these results in the QCM are compared with the available data from different experimental collabo-rations at LHC, RHIC, SPS and AGS. Three is the baryon-antibaryon flavor correlation factors. We provide predictions in cases of ignoring and considering the global flavor compensation of quarks and antiquarks, respectively, for comparison with the future measurements.The study shows that the results of the yield correlations of different light and strange hadrons in the QCM are consistent with the data from LHC (?)s=2.76TeV, RHIC (?)s=200,130,62.4,39;19.6,11.5GeV and SPS Ebeam=158,80,40,30AGeV, which justifies the quark combination in heavy ion collisions at these energies; but they disagree with the data from RHIC (?)s=7.7GeV, SPS Ebeam=20AGeV and AGS Ebeam=14.6,11.7,8AGeV, and even deviate seriously from the AGS data, which indicates the invalidity of the quark combination at these low reaction energies.(Ⅲ) With a few data of charm hadrons in Pb+Pb collisions at LHC published by the ALICE Collaboration, we extend the quark combination to the charm sector and point out that the measurement of the yields of hadrons with single charm valence quark can provide important insights into charm quark hadronization mechanism and properties of the hot and dense matter produced in high energy reactions. We propose several types of yield ratios of hadrons with single charm valence quark to measure various properties of low PT charm quark hadronization. We argue that ratios of open charm mesons as the function of PT can serve as good probes for the dynamics of charm quark hadronization.All the results we obtained in this thesis show that with the assumption of the fac-torization, the yields of different light, strange and charm hadrons exhibit a series of simple and interesting relations. These relations are independent of particular combina-tion models, independent of precise forms of quark joint momentum distributions and quark combination functions and they are the general results of the quark combination. They are valid as long as the quark combination is at work and the factorization as-sumption is valid, so they can be used to test the validity of the quark combination. The experimental data at LHC, high RHIC and SPS energies agree well with these results obtained in the general quark combination mechanism, which shows the validity of the quark combination and further indicates the deconfined QGP has been produced in these collision energies. The data at low energies, i.e., at AGS energies, deviate from these results in the QCM. This suggests the invalidity of the quark combination and further indicates QGP has not been created in such low energy collisions.更多还原