Investigation of Nuclear Structure with Intermediate-Energy Photons

核子的结构和夸克在确定这种结构中的作用的研究将在托马斯·杰斐逊国家加速器设施（杰斐逊实验室）的B厅使用标记光子系统进行。光子标记器大部分是由美国天主教大学（CUA）小组设计和制造的，它测量在核目标中产生反应的光子的能量。然后用CEBAF大接受度光谱仪（CLAS）测量反应产物。CUA组是CLAS协作的积极参与者，CLAS协作是许多用户组的伙伴关系，致力于构建和使用B厅的仪器来同时执行各种实验。在CLAS计划的初始阶段，CUA小组最深入地参与了两个实验：奇异粒子（K介子和超子）的光产生，以及π介子光产生的螺旋结构。前一个实验旨在探测奇异夸克在质子中的作用，将提供比以前可用的数据样本大100倍以上的数据样本。后者需要偏振光子束和偏振质子靶，将构成对Drell- Hearn-Gerasimov和规则的测试的一部分，该规则是全世界感兴趣的基本量。CUA小组还参与了两个使用没有CLAS的标记光子束的实验：一个是测量重核的光裂变概率，一个是测量π介子的罕见衰变。

A study of the structure of nucleons and the role of quarks in determining this structure will be performed using the tagged photon system in Hall B at the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory). The photon tagger, which was in large part designed and built by the Catholic University of America (CUA) group, measures the energy of the photon that produces a reaction in a nuclear target. The reaction products are then measured by the CEBAF Large Acceptance Spectrometer (CLAS). The CUA group is an active participant in the CLAS Collaboration, a partnership of many user groups devoted to constructing, and using the instrumentation in Hall, B to perform a variety of experiments concurrently. During the initial phase of the CLAS program, the CUA group is most deeply involved in two experiments: the photoproduction of strange particles (K mesons and hyperons), and the helicity structure of pi meson photoproduction. The former experiment, designed to probe the role of strange quarks in the proton, will provide a data sample more than 100 times larger than that previously available. The latter, requiring both a polarized photon beam and a polarized proton target, will constitute part of a test of the Drell- Hearn-Gerasimov sum rule, a fundamental quantity of worldwide interest. The CUA group is also participating in two experiments which use the tagged photon beam without the CLAS: a measurement of the photofission probabilities for heavy nuclei, and a measurement of the rare decays of the phi meson.