高能强子–强子碰撞中硬软过程的比较分析

根据QCD中“圆锥定义”来确定喷注,对高能强子-强子碰撞中的硬、软过程作细致的分析.用Pythia产生蒙特卡罗模拟样本,得到的喷注赝快度分布在中心区有平台,喷注内部的粒子密度和横能密度,随离喷注轴的距离指数地下降,比较发现对整个事件样本,单事件平均横动量或最大横动量与多重数是正关联的,而对喷注事件它们是负关联的.引入两个物理量来描述喷注事件的硬、软程度.发现它们与单事件平均横动量是正关联的,而与多重数是负关联的.表明用单事件平均横动量比用多重数能更好地描述喷注事件的硬软程度.     

α模型中不固定多重数下的阶乘矩、粒子数关联矩

利用二维相空间自仿射分形的随机级联α模型,采用蒙特卡罗模拟的方法,研究了阶乘矩､粒子数关联矩在不固定多重数下,对应于多重数相对起伏强度n_f的依赖关系,得到:阶乘矩、粒子数关联矩依赖于多重数相对起伏n_f,但间歇指数一般不依赖于n_f,当n_f较小时这种依赖性得以消除.     

快度间隔分析与逐事件快度关联

本文推导了逐事件快度间隔的起伏与逐事件快度关联的关系. 分析表明：快度间隔分析中新的和有意义的部分是推广的两粒子快度关联矩. 对于一些特殊的两粒子和矩阶数这些矩有明确的物理意义.     

阶乘矩的归一化与间歇指数对平均横动量的依赖性

本文对阶乘矩的两种不同归一化进行了细致的分析,发现在固定多重数以及间歇程度不依赖于多重数的情况下,两种归一化得到的间歇指数相等.对于多重数不固定,而间歇程度与多重数有关的情况,给出了两种不同归一化得到的间歇指数用动力学间歇指数表示的公式.本文还在间歇程度依赖于单事件平均横动量的假定下,全面复现了实验上观察到的间歇对横动量截断的依赖性,证实了平均横动量对于决定间歇程度有重要意义.     

阶乘矩的归一化与间歇指数对平均横动量的依赖性

本文对阶乘矩的两种不同归一化进行了细致的分析,发现在固定多重数以及间歇程度不依赖于多重数的情况下,两种归一化得到的间歇指数相等。对于多重数不固定,而间歇程度与多重数有关的情况,给出了两种不同归一化得到的间歇指数用动力学间歇指数表示的公式。本文还在间歇程度依赖于单事件平均横动量的假定下,生面复现了实验上观察到的间歇对横动量截断的依赖性,证实了平均横动量对于决定间歇程度有重要意义。     

强子-强子碰撞中平均横动量随多重数变化的能量关联与三火球模型

利用三火球模型,对强子-强子碰撞中平均横动量和多重数的关系进行了计算,根据两个侧边火球贡献的变化,成功地解释了在ISR顶峰能量以下平均横动量与多重数关系曲线的斜率为负、并随能量的升高而增加、以及多重数低时平均横动量近似地与能量无关的现象.     

158GeV/c的Pb–Pb碰撞中的J/ψ抑制现象研究

在Blaizot等人建立的模型基础上,我们考虑了核–核碰撞中的参与者数与核子–核子碰撞数的起伏效应对J/?ψ产生的影响,并对NA50合作组在入射动量为158GeV/c的Pb-Pb碰撞中的实验数据进行了分析,理论结果与实验数据符合的很好     

s=630GeV pp碰撞中微喷注的新分析

根据喷注判定的圆锥法来判断喷注,重新分析了UA1-1985年的s=630GeV非单衍pp碰撞实验数据. 分析发现对事件样本,单事件平均横动量p_t与多重数n是正关联的,而对喷注事件子样本则是负关联的;分析了微喷注产生的关联和退关联,表明微喷注产生来源于非软过程和高阶效应;并首次从实验上观测到微喷注间存在大快度间隔内无粒子的事例,分析了微喷注产生时存在大快度gap的迹象.     

高能多粒子末态的多重分形维数与动力学起伏强度

研究了多重分形维数与动力学起伏强度的关系,给出了一个能直接描述高能多粒子末态动力学起伏强度的特征参量,并指出了这一参量的适用范围以及在实际高能实验中的应用.     

夸克喷注和胶子喷注硬度特性的研究

用蒙特卡洛模拟方法研究了Z⁰强子衰变中的三喷注事件.用b标记方法辨别,得到夸克喷注和胶子喷注.定义了一个新的物理量—硬度.分别计算了发射了胶子的夸克喷注和胶子喷注的硬度分布.通过胶子和夸克喷注的平均多重数和平均横动量对硬度的依赖性以及他们的多重数和横动量在相同硬度区间内的分布情况的计算与比较,发现夸克喷注和胶子喷注的硬度特性有显著的差别.夸克喷注的特性几乎与硬度无关,而胶子喷注的特性与硬度之间存在较强的关联.当Hd>10GeV时,胶子喷注的平均多重数和平均横动量都明显地大于夸克喷注的平均多重数和平均横动量;而当H_d<6GeV时,结果正好相反.这表明,只是对于较硬的胶子,胶子喷注比夸克喷注“胖”的结论才能成立.     

Transverse-momentum fluctuations in pi(+)p and K(+)p Collisions at 250 GeV/c

We report results on event-by-event fluctuations of transverse momentum, Phi(p(t)), in pi(+)p and K(+)p collisions at 250 GeV/c. For the first time, their dependence on rapidity region, transverse momentum acceptance, multiplicity, mean transverse momentum per event, and on the correlation between transverse momentum and multiplicity are systematically presented. The results are compared with those from the PYTHIA Monte Carlo generator. The fluctuations under the same acceptance cuts as used in current heavy-ion experiments are also presented.     

利用HIJING产生器对RHIC能区质子反质子产额比的研究

利用HIJING 2.0 Monte Carlo事件产生器产生了RHIC能区(质心系能量130GeV和200GeV)的Au+Au最小无偏碰撞事件.对产生的事件样本进行分析表明:碰撞参数与事件的多重数有近似线性依赖关系,两者都可用来表征碰撞的对心度;质子反质子产额比不明显依赖于碰撞对心度、横动量、快度和事件平面.     

Investigation of Antiproton to Proton Ratioby HIJING at RHIC Energies

The HIJING 2.0 is used to generate Monte Carlo events for Au+Au minimum biased collisions at RHIC energies-sNN=130 and 200 GeV. Using the Monte Carlo event sample, it is shown that the impact parameter has approximately a linear dependence on multiplicity. Both of them can be used as characteristic quantity for centrality. The results on the /p ratio show that this ratio does not change remarkably with centrality, transverse momentum and rapidity, and is independent of the reaction plane within the HIJING model.     

Comparison of the Hard and Soft Processes in High Energy Hadron-Hadron Colisions

Using the“con ealgorithm”in QCD to identify jet,the hard and soft processes in high energy hadroncic olisions are analysed indetail.A Monte Carlo simulation event sample is produced by PYTHIA.The resultant pseudorapidity distribution of jets has a plateau in the central region.The particle and transverse energy density in jets decreases exponentially with the increase of the distance from particles to jet axis.Through comparisons,we find the event average transverse momentum or maximum transverse momentum is positively correlated with multiplicity for the whole event sample,and negatively correlated with multiplicity for jet event subsample.Two ratio variables well describe the hardness of jet events,and they are positively correlated with the event average transverse momentum and negatively correlated with multiplicity,which confirms the event average transverse momentum is a better characteristic quantity to describe the hardness of jet events than multiplicity.     

用第一级反应平面测量重离子碰撞中逐事件椭圆流涨落的一种方法

A new method is presented for measuring event-by-event fluctuations of elliptic flow (v₂) using first-order event planes. By studying the event-by-event distributions of v₂ observables and first-order event-plane observables, average flow 〈v₂〉and event-by-event fluctuations with respect to that average can be separately determined, making appropriate allowance for the effects of finite multiplicity. The relation of flow fluctuations to eccentricity fluctuations in the initial-state participant region, as well as detector acceptance effects, are discussed.     

强子–强子碰撞中硬分量存在的又一实验证据

对sqr(s)=540Gev能量下的高能强子-强子碰撞得到的单事件平均横动量p. 对多重数N的散点图进行了仔细分析后指出;其中大多重数、大事件是碰撞过程中出现硬分量的又一个实验证据,并用仅含软分量的单分量模型和既含软分量又含硬分量的二分量模型的Monte Carlo模拟定性地证实了这一论断.     

Factorial Moments and Factorial Correlations in α Model for Non-Fixing Multiplicity

Using the self-affine fractal of two-dimensional phase space and Monte Carlo simulation, the dependence of the factorial moments and the factorial correlations on the multiplicity relative strength of fluctuation are studied for non-fixing multiplicity. It is discovered that the factorial moments and the factorial correlations depend on the muldplicity relative strength of fluctuation n_f, but the intermittency does not depend on n_f When n_f is smaller, these dependence are dispelled.     

Methods to study event-by-event fluctuations in the NA61/SHINE experiment at the CERN SPS

Theoretical calculations locate the critical point (CP) of strongly interacting matter at energies accessible at the CERN SPS. Event-by-event transverse momentum and multiplicity fluctuations are considered as one of the most important tools to search for the CP. Pilot studies of the energy dependence and the system size dependence of both p _T and multiplicity fluctuations were performed by the NA49 experiment. The NA61/SHINE ion program is a continuation of these efforts. After briefly recalling the essential NA49 results on fluctuations we will discuss the technical methods (removing Non-Target interactions) which we plan to apply for future transverse momentum and multiplicity fluctuation analyses.     

Event-by-event fluctuations of average transverse momentum in central Pb+Pb collisions at 158 GeV per nucleon

We present first data on event-by-event fluctuations in the average transverse momentum of charged particles produced in Pb+Pb collisions at the CERN SPS. This measurement provides previously unavailable information allowing sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-event average transverse momentum is consistent with independent particle production modified by the known two-particle correlations due to quantum statistics and final state interactions and folded with the resolution of the NA49 apparatus. For two specific models of non-statistical fluctuations in transverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement.