中国极化电子离子对撞机计划

轻子散射实验是探索核子与原子核结构的理想工具。中国电子离子对撞机(Electron Ion Collider in China,EicC)建议书设想在已开建的强流重离子加速器装置(High Intensity heavy ion Accelerator Facility,HIAF)的基础上,升级质子束流为20 GeV的极化束流,并建造2.8~5 GeV极化电子束流,从而实现质心系能量为15~20 GeV的双极化电子-离子对撞。EicC设计的亮度为(2~4)×10^33cm^-2·s^-1,质子束流极化率达到70%,电子束流极化率达到80%。该装置除了能提供极化轻离子束流(例如:氦-3)外,也可产生非极化重离子束流(碳-12~铀-238)。EicC将聚焦核子海夸克部分子结构、原子核物质结构与性质、奇特强子态三个方面的物理研究。高亮度、高精度的对撞机有助于精确地测量核子结构函数并对核子进行三维成像,揭示强相互作用的动力学规律;原子核部分子分布包括核子短程关联以及原子核介质效应同样是该提案的重要科学目标;EicC能区接近重味夸克产生阈值,在研究重味强子谱方面拥有低背景的独特优势,有助于发现研究新的奇特强子态。质子质量起源问题也可以通过重味矢量介子的产生来研究。为了完成上述物理目标,我们将利用最先进的探测器技术建造接近全立体角覆盖的EicC对撞机谱仪。在准备EicC白皮书的过程中,我们得到世界各国专家的支持。EicC的物理与已有的实验和美国即将建设的EIC中的物理项目相互补充。EicC的建成及运行有望引领前沿的中高能核物理研究,使我国在加速器和探测器先进技术等领域实现跨越式发展,为我国核物理与强子物理以及相关科学领域提供大型综合实验平台与人才培养基地。

格点量子色动力学数据的虚部分布与信号改进

通过分析淬火近似下高统计量格点两点关联函数实部与虚部对规范场采样的分布,给出了一种可能的实、虚部分布间的定量关系,并通过计算实部与虚部的非平庸统计相关性对该关系加以验证.利用该实、虚部的统计相关性,格点关联函数的方差可以得到约40%的改进.这些结果为进一步理解格点计算中统计误差的物理来源以及发展信号改进方案提供了全新的思路.

Exotic vector charmonium and its leptonic decay width

We propose a novel type of interpolating field operator, which manifests the hybrid-like configuration that the charm quark-antiquark pair recoils against gluonie degrees of freedom. A heavy vector charmonium-like state with a mass of 4.33（2） GeV is disentangled from the conventional charmonium states in the quenched approximation. This state has affinity for the hybrid-like operators but couples less to the relevant quark bilinear operator. We also try to extract its leptonic decay constant and give a tentative upper limit that it is less than one tenth of that of J/ψ, which corresponds to a leptonic decay width about dozens of eV. The connection of this state with X（4260） is also discussed.

Mass spectrum and strong decays of strangeonium in a constituent quark model

In this work we calculate the mass spectrum of strangeonium up to the 3D multiplet within a nonrelativistic linear potential quark model.Furthermore,using the obtained wave functions,we also evaluate the strong decays of the strangeonium states with the ^3P_0 model.Based on our successful explanations of the well established states φ(1020) , φ(1680) , h_1(1415) , f'_2(1525) ,and φ_3(1850) ,we further discuss the possible assignments of strangeonium-like states from experiments by combining our theoretical results with observations.It is found that some resonances,such as f_2(2010) and f_2(2150) ,listed by the Particle Data Group,and X(2062) and X(2500) ,newly observed by BESIII,may be interpreted as strangeonium states.The possibility of φ(2170) as a candidate for φ(3S) or φ(2D) cannot be excluded.We expect our results to provide useful references for looking for the missing s\bar{s} states in future experiments.

胶球的格点QCD研究

胶球是强子物理的重要研究对象,也是我国北京谱仪(BESⅢ)实验寻找的重要物理目标。格点量子色动力学作为从第一性原理出发的研究强相互作用非微扰特性的方法,是研究胶球问题的重要理论工具。本工作介绍了近年来格点量子色动力学理论对胶球性质的一些研究进展,并讨论实验上发现的若干共振态作为胶球的可能性。另外,规范场拓扑荷密度在纯规范理论中可以作为内插场算符来研究赝标量胶球性质,但在具有u,d,s动力学海夸克组态上的拓扑荷密度算符的关联函数中,只观察到轻赝标量介子η和η’的贡献。这启示我们在具有动力学海夸克的情形下,需要构造多种形式的内插场算符来研究赝标量胶球。

Glueball spectrum from Nf=2 lattice QCD study on anisotropic lattices

The lowest-lying glueballs are investigated in lattice QCD using Nf = 2 clover Wilson fermions on anisotropic lattices. We simulate at two different and relatively heavy quark masses, corresponding to physical pion masses of mπ～938 MeV and 650 MeV. The quark mass dependence of the glueball masses has not been investigated in the present study. Only the gluonic operators built from Wilson loops are utilized in calculating the corresponding correlation functions. In the tensor channel, we obtain the ground state mass to be 2.363（39） GeV and 2.384（67）GeV at mπ～938 MeV and 650 MeV, respectively. In the pseudoscalar channel, when using the gluonic operator whose continuum limit has the form of ∈_ijkTrB_iD_jB_k, we obtain the ground state mass to be 2.573（55） GeV and 2.585（65） GeV at the two pion masses. These results are compatible with the corresponding results in the quenched approximation. In contrast, if we use the topological charge density as field operators for the pseudoscalar, the masses of the lowest state are much lighter（around 1 GeV） and compatible with the expected masses of the flavor singlet qq meson. This indicates that the operator ∈ijk TrBiDjBk and the topological charge density couple rather differently to the glueball states and qq mesons. The observation of the light flavor singlet pseudoscalar meson can be viewed as the manifestation of effects of dynamical quarks. In the scalar channel, the ground state masses extracted from the correlation functions of gluonic operators are determined to be around 1.4-1.5 GeV, which is close to the ground state masses from the correlation functions of the quark bilinear operators. In all cases, the mixing between glueballs and conventional mesons remains to be further clarified in the future.