多夸克态研究简述

介绍了多夸克态的研究现状. 主要介绍了四夸克态、五夸克态和双重子态的理论研究. 并列举了实验上观察到的可能是多夸克态的粒子或共振态.     

多夸克态研究概况

介绍了多夸克态研究的重要性,侧重介绍了最近发现的5夸克态的实验和理论研究现况.     

Jaffe与Wilczek双夸克模型中的负宇称五夸克态

如果Jaffe与Wilczek关于Q5+五夸克态的双夸克图像是正确的话,那就应该存在负宇称的五夸克SU(3)八重态与单态,其中两个双夸克间没有轨道激发.这些态比Q5+质量低,与传统夸克模型中的由三夸克构成的重子的轨道激发质量接近.我们计算了这些负宇称态的质量与磁矩,用手征有效拉氏量讨论了他们可能的强衰变模式和选择定择，发现有两个态可能比较窄.我们建议实验上寻找这九个额外的负宇称态.如果将来的实验确实发现了这些态,那是对Jaffe与Wilczek双夸克模型的直接验证.否则,应该重新评估Jaffe与Wilczek的双夸克图像甚至抛弃这个模型.     

奇特的"五夸克态"和重子中的五夸克成分

文章简要介绍了奇特的θ^＋五夸克态、质子中的奇异夸克成分和重子激发态中的五夸克成分等重子谱和重子结构方面的一些最新前沿进展．最新的高统计量实验结果表明，轰动一时的suudd五夸克态θ^＋（1540）很可能不存在．而最新的几个电弱相干实验给出一致的结果：质子的奇异磁矩和奇异半径很可能不为零，且均为正．理论分析表明，这意味着质子中的ssuud成分很可能主要是以夸克对有色集团的形式存在，而不是以传统的介子云无色集团的形式存在．对最轻的负宇称核子激发态N^＊（1535）一些性质的最新研究支持这种关于重子中的五夸克成分的新图像．     

宇称为正角动量为3/2的五夸克态的磁矩

如果将来的实验证实五夸克态Θ+ 5与Ξ- - 5的JP=12+ ,在一些理论模型中,JP=32+ 与JP=12+ 的五夸克态必然同时出现.这些态有可能很快会发现.我们在不同理论模型中计算了JP=32+ 的五夸克态的磁矩.     

寻找多夸克新粒子态的实验进展

文章叙述了强子结构的夸克模型的成就和不足,详细介绍了寻找多夸克新粒子态的实验进展.寻找多夸克新粒子态对中国粒子物理实验学家可能作出世界创新成果是一个良好机遇.     

重子中七夸克成分qqq(qˉq)2的低位能谱

在非相对论夸克模型内,利用手征超精细相互作用,把原来对五夸克系统qqqqˉq能谱的预言,扩展到了七夸克系统qqq(qˉq)2的基态和轨道第一激发态能谱的计算,所使用的参数也是来自于五夸克系统.预言了最低七夸克态的能量大约是2.1 GeV,自旋-宇称是JP=1也存在一些三夸克系统和五夸克系统,所以能量在2 GeV以上的重子激发态可能是这3种夸克成分的混合.+或者JP=1?.由于在这个能区22     

神奇有趣的五夸克态

对今年国际上有关五夸克态的实验与理论研究现状作一个总体的评述 ,指出了有待解决的主要问题和相关的一些背景知识 ,并简单介绍了作者所在研究小组的有关研究工作 .     

电子-离子对撞机上开展核子及其激发态研究的建议

核子及其激发态性质研究一直是中高能核物理的一个重要研究领域。然而,到目前为止,对核子及其激发态内部结构的了解还处在初级阶段。首先介绍了核子及其激发态研究现状,指出了三夸克模型在描述核子特别是核子激发态内部结构方面存在很大的缺陷。为解决传统三夸克模型的不足,有一种新的观点认为虽然独立的五夸克态不存在,但是核子及其共振态中存在可观的五夸克激发。这种五夸克图像提供了一个描述核子内部结构的新见解,给出了与经典三夸克图像相当不同的核子激发态谱预言,还有待实验检验。目前国内外正在论证的电子–离子对撞机(EIC)将是研究核子结构下一代最重要的加速器装置,被视为"超级电子显微镜"。由于EIC有较高的能量和亮度,特别是低本底等优势,可以开展核子及其激发态性质的研究以及新强子态研究。     

五夸克态Θ的手征夸克模型研究(英文)

在手征夸克模型的框架下, 研究了五夸克态 uudd的结构. 分别考虑了 Jπ=(1/2)-和Jπ=(1/2)+的各四个组态. 结果表明对于不同的模型, 不论 Jπ=(1/2)-和 Jπ=(1/2)+, T=0的态的能量总是最低的. 但是最低态的能量的理论计算值仍比Θ质量的实验值高250—300 MeV.     

Pentaquark Update

the pentaquark has drawn great attention during the last two years in 2003 and 2004. this paper gives a relatively extensive review of the experimental and theoretical progress in the research of the pentaquark, including the contributions from several chinese groups. some open questions on pentaquark study are also discussed.     

Hidden-charm Pentaquark Production at e~+e~- Colliders

We study one possible production mechanism for the hidden-charm pentaquark via a color-octet cc pair fragmentation in e~+e~-collision.The pentaquark production at B factory energy is dominated by e~+e~-→ccg→P_c+X,while at Z~0pole energy,there are several partonic processes playing significant role.Our results show that it is possible to search for the direct pentaquark production signal at e~+e~-colliders,which is important to understand the properties of pentaquark.     

Understanding pentaquark States in QCD

We estimate the mass of the pentaquark state with QCD sum rules and find that pentaquark states with isospin I=0,1,2 lie close to each other around (1.55+/-0.15) GeV. The experimentally observed baryon resonance Theta(+)(1540) with S=+1 can be consistently identified as a pentaquark state if its J(P)=1 / 2(-). Such a state is expected in QCD. If its parity is positive, this pentaquark state is really exotic. The outstanding issue now is to determine its quantum numbers experimentally.     

Structure and reactions of pentaquark baryons

We review the current status of the exotic pentaquark baryons. After a brief look at experiments of both positive and negative results, we discuss theoretical methods to study the structure and reactions for the pentaquarks. First we introduce the quark model and the chiral soliton model, where we discuss the relation of mass spectrum and parity with some emphasis on the role of chiral symmetry. It is always useful to picture the structure of the pentaquarks in terms of quarks. As for other methods, we discuss a model-independent method, and briefly mention the results from the lattice and QCD sum rule. Decay properties are then studied in some detail, which is one of the important properties of ⊝⁺. We investigate the relation between the decay width and the quark structure having certain spin-parity quantum numbers. Through these analyses, we consider as plausible quantum numbers of ⊝⁺,J ^P = 3/2⁻. In the last part of this note, we discuss production reactions of ⊝⁺ which provide links between the theoretical models and experimental information. We discuss photoproductions and hadron-induced reactions which are useful to explore the nature of ⊝⁺     

Pentaquarks in high-energy colliding experiments: perspectives from HERA

Several issues related to pentaquark searches relevant for current and future high-energy colliding experiments are discussed. We make an attempt to explain why pentaquark candidates are not seen by some experiments, and what makes the HERA experiments so special in such searches. Received: 7 March 2005, Published online: 27 September 2005     

Calculation of the pentaquark width using QCD sum rules

The pentaquark width Γ_? has been calculated using the QCD sum rules. The estimate shows that the width does not exceed 1 MeV. The main conclusion is that the sum rules indeed predict a narrow width of the pentaquark ?⁺, and the decay width is suppressed both parametrically and numerically.     

Magnetic moments of heavy flavour pentaquarks

The magnetic moments and radii of the P , P and P _s pentaquark states are calculated in the framework of the bound-state model for the hyperons, according to which these states are predicted to be weakly bound. The magnetic moments for the two lowest pentaquark states in both nonstrange flavour sectors are predicted to be vanishingly small.     

Dynamical Calculation of Θ+ Mass and Decay width in the Quark Model

In this paper we study the mass splitting and the decay width of pentaquark (Θ⁺) at the ground states in the framework of flux tube, quark delocalization and color screening model. We consider the pentaquark as diquark-triquark configuration and obtained closer values of mass splitting and the decay width of Θ⁺ to the experimental data.     

In-Medium Effective of Pentaquark Θ+ in the Density Dependent Relativistic Hadron Field Theory

The density dependent relativistic hadron field theory is extended to inclusions of pentaquark Θ⁺. We have investigated the mass modifications of nucleons and pentaquark Θ⁺ in the framework of relativistic mean field theory. We find that the effective mass, of either the nucleon or the pentaquark Θ⁺ decreases as baryon density increases. We have studied the effects of the fractions of Θ⁺ and neutron on the baryon masses. We also discussed the relations between scale density ρ_S and vector density ρ_B at different baryon fractions.