The Structure of Hadrons with Electromagnetic Probes

经历强核力的粒子几乎构成了地球上所有物质的质量，在宇宙的组成中起着决定性的作用。因此，了解它们的结构具有重大的科学意义。这样的粒子叫做强子。强子主要有两种，一种是重子，如质子和中子，主要由三个夸克组成，另一种是介子，主要由夸克-反夸克对组成。RPI小组专门研究强子的非常小的亚结构，并发现不寻常的或外来的强子，这些强子不能用通常的3夸克或夸克-反夸克内容来描述。最近，RPI小组在发现几个具有不寻常或外来结构的状态方面发挥了重要作用。它们包括可能是五夸克态的外来重子，和外来介子，可能有一个夸克和一个反夸克加上一个胶子，或者只由胶子组成的介子。这些发现可能表明许多新粒子尚未被观察到。在下一个拨款期内，托马斯·杰斐逊国家加速器设施和康奈尔电子存储环的光子和电子束将用于探测强子的结构，并寻找新的外来粒子。为了更好地理解强核力，将对这些粒子的结构以及其他粒子进行研究

Particles that experience the strong nuclear force constitute nearlyall the mass of of matter on earth and play decisive roles in thecomposition of the universe. Thus, understanding their structure is ofgreat scientific interest. Such particles are called hadrons. There aretwo major classifications of hadrons, baryons, such as protons andneutrons, which are made primarily of three quarks, and mesons, whichare made primarily of quark-antiquark pairs.The RPI group specializes in the study of the very small substructureof hadrons, and discovering unusual, or exotic, hadrons which cannot bedescribed in terms of the usual 3-quark, or quark-antiquark contents.Recently, the RPI group has played major roles in the discovery ofseveral states having unusual, or exotic, structure. These includeexotic baryons that may be five-quark states, and exotic mesons,possibly having a quark and an anti-quark plus a gluon, or mesons madeof only gluons. These discoveries may indicate that many new particleshave not yet been observed.During the next grant period photon and electron beams at the ThomasJefferson National Accelerator Facility and at the Cornell ElectronStorage Ring will be used to probe the structure of hadrons, and tosearch for new exotic particles. The structure of these particles,among others, will be studied in order to achieve a betterunderstanding of the strong nuclear force.--