Studies of hadronic structure using electromagnetic probes

现代物理学研究的中心问题之一涉及到我们对原子核的组成部分--质子、中子和其他束缚它们的粒子(介子)--的理解。值得注意的发现表明，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(称为量子色动力学，或QCD)能够准确地描述夸克和胶子在极高能量下(或相当于当夸克非常接近时)如何相互作用，但将QCD应用于较低能量(较长距离)的现象一直是非常困难的。我们提高理解的障碍之一是缺乏高质量的数据，特别是提供QCD内部工作原理最清晰图景的深度排他性反应。这些研究是困难的，因为它们需要连续的、高光度的电子束，以及具有良好的粒子识别和可重现的系统学的探测器。Jefferson Lab(JLab)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.