相对论重离子碰撞中π介子椭圆流劈裂

近年来,美国布鲁克海文国家实验室的相对论重离子对撞机上正在进行着束流能量扫描实验, STAR国际合作组的研究人员发现π介子椭圆流劈裂与电荷不对称度存在着线性关系.该现象被认为是手征磁波效应的重要信号.本文基于拓展的多相输运模型,利用三味Nambu-Jona-Lasinio (NJL)模型研究了构成π⁺和π^-介子不同的夸克同位旋平均场势,为解释π介子椭圆流劈裂与电荷不对称度线性关系的实验现象提供了新思路,可为同质异素体碰撞以及致密星体中夸克物质同位旋效应研究提供理论依据.     

π介子的非对称发射与核媒质态方程

本文采用VUU模型研究了1.8AGeV Ar+Pb碰撞中π介子子非对称发射携带的核物质态方程信息.指出在靶核旁观者吸收较弱的入射核快度区域,末态π介子的集体运动中保留着同重子集体关联类似的特性.其发射方位角分布的非对称性是对核物质态方程敏感的参量.由π介子方位角关联函数方法对Bevalac激光室1.8AGeV Ar+Pb碰撞实验数据的分析结果和对硬核媒质态方程模型模拟事件的计算相符合.     

B→π跃迁形状因子中扭度为3的分布振幅

我们选择了恰当的手征流关联函数,用光锥QCD求和规则去计算B到π的跃迁形状因子,得到的结果仅仅依赖于π介子的3扭度光锥分布振幅.这样从f+?Bπ的研究中,我们就可以对π介子的3扭度光锥分布振幅给出一个约束条件.     

核物理中的π介子

在强子层次上,原子核或强子物质的基本组元是核子和介子.弄清这些强子的结构,并由基本原理出发研究它们的性质,是当代核物理的重要课题.在各种介子中,π介子是最轻且最重要的介子.关于自由空间中π介子的结构与性质、核介质内π介子的性质、π 核子相互作用与π 核相互作用等问题,始终受到相当多的关注.π介子在核物理中的作用直接联系着手征对称性,汤川秀树关于π介子的最初概念已经大大发展了.有清楚的实验证据表明,核内存在π介子的集体模式,这种集体模式与以前观测到的所有核集体运动模式截然不同.拟对π 核物理的研究现状及值得进一步研究的主要问题予以简要评述. At the hadronic level, nucleons and mesons are constituents of nuclei and hadronic matter. Understanding the structures of hadrons, finding the physics of how the properties of these particles arise from the first principle, are major interests in modern nuclear physics. Among mesons, the lightest and most important one is certainly the pion, thus it is no accident that its structure, properties (both in free space and in nuclear matter) and interactions with nucleons and nuclei have gotten considerable ...     

π介子单电荷交换对无中微子双β衰变的贡献

本文计算了π介子单电荷交换机制对传递重中微子的0νββ衰变振幅的贡献,并与以前的π介子双电荷交换机制下的计算结果进行了比较,我们发现:对此衰变有重要贡献的π介子自由度只是π介子双电荷交换机制.     

介绍一种“π凝聚”的理论模型

一、引言 π分子是一种基本粒子,属介子旅.根据据所带电荷为 、 、0,可分为π ,π-,πu三种π介子π介子的自旋转为零,宇称为负,同位旋为1,静止质量为139, 物理MeV,寿命为10-8see.它在核物理中占有十分突出的地位.自从1935年日本　川秀树提出了核力介子理论以来,现在一般都认为,核子-核了间的相互作用是通过π分子来传递的。在原子核内存在着瞬时出现的π介子,与自由π介子不同,它不满足的质能关系式,因此说它是“虚”的π介子. 最近几年,有不少理论物理工作者[1]在探讨这样一个问题:在原子核内是否有真实的自由π介子存在?他们考虑的基点…     

热密π介子环境中的ρ介子谱函数

利用描述ρ-π耦合的有效模型, 研究了热密π介子环境中的ρ介子谱函数. 数值计算的结果表明, 随着温度和π介子化学势的升高, 谱函数变宽, 且峰的位置向高不变质量区移动.     

核物质中内介质等效手征Lagrange量和π介子质量

在核物质中从手征等效Lagrange量得到的π介子有效质量是单值的,并且与π介子场的离壳扩展无关,例如PCAC选择.同位旋对称核物质中的有效π介子质量随增加的核密度有些上升,因此有效类时π介子衰变常数和密度相关的夸克凝聚渐渐下降.另外研究了内介质Gell–Mann–Oakes–Renner关系和其它内介质同一性.最后讨论了同位旋对称、各向同性和均匀的核物质中关于介子传播的等效Lagrange量的几个限制.     

π介子结构函数的一种可能形式

本文利用量子色动力学中强子波函数的福克组态展开讨论了π介子结构函数的行为.并以一种福克组态模型波函数作为例子, 对高福克态引入了具有Regge行为的权重函数, 从而获得了一种可能的π介子结构函数形式. 这一形式与实验上所得的π介子结构函数数据相一致.     

关于重原子核的自发π介子发射问题

本文建议用测量单举高能γ射线的方法探测文献[1]提出的重原子核自发π介子发射.用文献[1]给出的发射π介子能量最大值,计算了发射π⁰介子衰变的高能γ射线的能量范围.     

高能不等核碰撞和弛豫时间的相对论动力论方程描述

本文用相对论动力论方程描述高能重离子碰撞时空演化,并用它分析在200A GeV的¹⁶O束流和³²S束流下,于快度中心区的末态粒子快度分布,确定了不同系统的弛豫时间.     

Relativistic diffusion model

Evidence is presented that diffusion drives colliding many-particle systems at relativistic energies from the initial δ–functions in rapidity towards the equilibrium distribution. Analytical solutions of a linear Fokker-Planck equation represent rapidity spectra for participant protons in central heavy-ion collisions at SPS-energies accurately. Thermal equilibrium in the interaction region is not attained, nonequilibrium features persist and can account for the broad rapidity spectra. Received: 24 November 1998 / Revised version: 20 February 1999     

Mass spectrum of the dimuons produced in relativistic heavy-ion collisions

The mass spectrum of dimuons produced from the matter in the central region of rapidity in ultra-relativistic heavy-ion collisions is calculated in accordance with Bjorken’s recently proposed model for relativistic heavy-ion collisions. The matter in this central region is assumed to consist of a deconfined quark-gluon plasma phase and a pionized phase. Distinct enhancements of the dimuon mass spectrum below 500 MeV, due to the quark-gluon phase, are predicted for a deconfinement phase-transition temperatureT _c<200 MeV.     

Back-reaction in the presence of thermalizing collisions

Preequilibrium parton production following an ultrarelativistic nucleus-nucleus collision is studied in terms of the decay of a strong chromoelectric field which generates pairs through the Schwinger mechanism. Back-reaction of the partons with the field is included and a model transport equation containing a collision term is solved for the central rapidity region based on an approximation in which the partons relax to a thermal distribution.     

中心快度区的双轻子不变质量分布

推广先前作者采用的夸克和π的相空间分布函数的Boltzmann近似到一个完全的表示,利用快度区的温度计算出粒子密度后,在Bjorken的(1+1)维的纵向膨胀系统中研究了双轻子的产生.发现推广的近似分布函数很大地改变了预言的夸克物质形成的特征双轻子分布.     

Cold Nuclear Matter Effects on Isolated Prompt Photon and Isolated Prompt Photon+Jet Productions in Relativistic Heavy-Ion Collisions

We investigate the cold nuclear matter(CNM) effects on isolated prompt photon and isolated prompt photon associated jet productions in nuclear collisions at the NLO accuracy by using the EPS09 NLO nuclear parton distribution functions and their error sets.Nuclear modification factors of isolated prompt photon and isolated prompt photon+jet productions due to CNM effects in p+A and A+A reactions at the RHIC and the LHC are provided with varying rapidity and transverse momentum of the final state photon.It is shown that the CNM effects on isolated prompt photon and photon+jet are modest,which give a small enhancement at low pT region and a more obvious suppression at large pT at central rapidity.At forward rapidity a pronounced suppression of γ as well as γ+jet is always observed.     

利用深度学习方法研究核物质状态方程

对核物质状态方程的研究将有助于人们更好地了解原子核的性质以及宇宙和星体的演化过程等基本问题。重离子碰撞能产生高温高密核物质，利用输运模型的模拟结合相关实验数据的比较是研究核物质状态方程最常用方法之一。本文利用深度学习中的卷积神经元网络(CNN)方法对不同核物质状态方程给出的末态质子横动量和快度分布进行学习，使神经元网络具有从末态粒子信息来判断核物质状态方程软硬的能力。利用预测差异分析方法(Prediction Different Analysis)，可以找到横动量和快度分布中对状态方程最敏感的区域。此外，还测试了一种基于决策树的梯度提升算法(LightGBM)，发现得到的准确度和CNN方法类似。     

Rapidity distribution as a probe for elliptical flow at intermediate energies

The interplay between spectator and participant matter in heavy-ion collisions is investigated within the isospin-dependent quantum molecular dynamics (IQMD) model in terms of the rapidity distribution of light charged particles. The effect of different types and sizes of rapidity distributions is studied in elliptical flow. The elliptical-flow patterns show the important role of nearby spectator matter on the participant zone. This role is further explained on the basis of the passing time of the spectator and the expansion time of the participant zone. The transition from in-plane to out-of-plane emission is observed only when the mid-rapidity region is included into the rapidity bin. Otherwise no transition occurs. The transition energy is found to be highly sensitive to the size of the rapidity bin, while it is only weakly dependent on the type of the rapidity distribution. These theoretical findings are found to be in agreement with experimental results.     

Gluon saturation and baryon stopping in the SPS, RHIC, and LHC energy regions

A new geometrical scaling method with a gluon saturation rapidity limit is proposed to study the gluon saturation feature of the central rapidity region of relativistic nuclear collisions. The net-baryon number is essentially transported by valence quarks that probe the saturation regime in the target by multiple scattering. We take advantage of the gluon saturation model with geometric scaling of the rapidity limit to investigate net baryon distributions, nuclear stopping power and gluon saturation features in the SPS and RHIC energy regions. Predictions for net-baryon rapidity distributions, mean rapidity loss and gluon saturation feature in central Pb+Pb collisions at the LHC are made in this paper.     

BFKL ansatz for BK equation in conformal basis

The BK equation in the conformal basis is considered and analyzed. It is shown that at high energy a factorization of the coordinate and rapidity dependence should hold. This allows to simplify significantly the form of the equation under discussion. An analytical ansatz for the solution to the BK equation at high energies is proposed and analyzed. This analytical ansatz satisfies the initial condition at low energy and does not depend on both rapidity and the initial condition in the high energy limit. The case of the final rapidity being not too large is discussed and the properties of the transition region between small and large final rapidities have been studied.