Heavy gas Cerenkov detector for Jefferson lab

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、中子和其他结合它们的粒子（介子）的理解。一些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如何在极高的能量下相互作用（或者，当夸克非常接近时），但将QCD应用于较低能量（较长的距离）现象是非常困难的。矛盾的是，随着夸克-胶子相互作用的日益复杂，这些粒子变得越来越远，这对它们被限制在核构建块内至关重要，但我们无法进行必要的QCD计算来证实我们的理解。

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. The paradox is that the increasing complexity of the quark-gluon interaction as these particles become further apart is critically important to their confinement within the nuclear building blocks, but we cannot perform the QCD calculations necessary to confirm our understanding.