The Structure of Hadrons with Electromagnetic Probes

受到强核力作用的粒子几乎构成了地球上所有物质的质量，在宇宙的构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。这种粒子被称为强子。强子有两种主要的分类，重子，如质子和中子，主要由三个夸克组成，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子结构，并发现不寻常的或奇异的强子，这些强子不能用通常的三夸克或夸克-反夸克含量来描述。最近，RPI小组在发现几个具有不寻常或奇异结构的状态方面发挥了重要作用。 这些包括可能是五夸克态的奇异重子，奇异介子，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的粒子还没有被观测到。在下一个资助期内，位于华盛顿-杰斐逊国家加速器设施和康奈尔电子储存环的光子和电子束将被用来探测强子的结构，并寻找新的奇异粒子。 这些粒子的结构，除其他外，将被研究，以实现更好地理解强核力。

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.--