Studies of hadronic structure using electromagnetic probes

现代物理学研究的中心问题之一是我们对原子核的构建单元的理解-质子，中子和其他粒子（介子）将它们结合起来。 一些重要的发现表明，这些粒子由更基本的成分夸克和胶子组成。 虽然一个非常好的理论框架（称为量子色动学，或QCD）能够准确地描述夸克和胶子在极高能量下（或者等价地，当夸克非常接近时）如何相互作用，但将QCD应用于较低能量（较长距离）的现象非常困难。 我们提高理解的障碍之一是缺乏高质量的数据，特别是对于提供QCD内部工作的最清晰图像的深排他反应。 这些研究是困难的，因为它们需要连续的，高亮度的电子束，和探测器具有良好的粒子识别和可重复的系统。杰斐逊实验室（JLab）的12 GeV升级旨在解决这些问题。

One of the central problems of modern physics research concerns our understanding of the building blocks of the atomic nucleus -- the protons, neutrons, and other particles (mesons) that bind them. Notable discoveries have indicated that these particles consist of yet more fundamental constituents, the quarks and gluons. While a very good theoretical framework (called Quantum Chromo-Dynamics, or QCD) is able to describe accurately how quarks and gluons interact at extremely high energies (or, equivalently, when the quarks are very close together), it has been very difficult to apply QCD to lower energy (longer distance) phenomena. One of the obstacles to our improved comprehension has been a lack of quality data, particularly for the Deep Exclusive Reactions which provide the clearest picture of the inner workings of QCD. These studies are difficult because they require continuous, high luminosity electron beams, and detectors with good particle identification and reproducible systematics. The Jefferson Lab (JLab) 12 GeV upgrade is intended to address these issues.