Hadron Spectroscopy using Polarized Photons

高能光子在质子上的散射问题已经被研究了几十年。对这一努力的长期兴趣在很大程度上是由对核子和介子激发的研究推动的，核子和介子激发表现为核子内部夸克的特定配置。随着高能、高极化光子束和超冷极化靶的发展，使核子自旋的取向保持在几毫升开尔文，我们终于能够以偏振可观的形式测量散射幅度的所有分量，从而明确地解开对散射的共振贡献。CUA是该项目的领先机构，该项目正在弗吉尼亚州纽波特新闻的托马斯·杰斐逊国家加速器设施(JLab)的B大厅进行。加州大学的两名研究生正在提取光子和质子相互作用的所有偏振观测数据，在这些粒子中会产生所谓的奇怪粒子，这种粒子在自然界中不存在，但只在高能散射中出现。他们的研究奠定了该计划的基石。强相互作用理论预测了介子中将夸克和反夸克紧密结合在一起的胶水的激发，但尚未在实验上建立。JLab正在建设的GlueX实验将致力于寻找这种激发。通过使用高能、高度偏振的光子束和完全覆盖的高分辨率探测器，GlueX实验有望解决这个问题。CUA对实验的贡献是建造和维护宽带标记示波器和偏振光子源。该建设项目为加州大学物理和工程专业的本科生提供了极好的研究机会，他们将被指导在霍氏望远镜的原型制作、建造和测试中发挥关键作用。NSF提供的赠款将支持CUA在JLab B厅的冷冻自旋目标计划以及GlueX建设项目中所做的努力。

The scattering of high energy photons on protons has been studied for many decades. The long interest in this endeavor is largely motivated by the study of nucleon and meson excitations, which manifest themselves as specific configurations of quarks inside the nucleon. With the development of high energy, highly-polarized photon beams and ultra-cold polarized targets, which keep the orientation of the nucleon spin frozen at a few milliKelvin, we finally are able to measure all components of the scattering amplitudes in the form of polarization observables, and thus to disentangle unambiguously the resonant contributions to the scattering. CUA is a leading institution in this program that is being conducted in Hall B at the Thomas Jefferson National Accelerator Facility (JLab) in Newport News, VA. Two CUA graduate students are extracting all polarization observables for the interaction of photons and protons in which so-called strange particles are produced, particles that do not occur in nature but only in high-energy scattering. Their research builds the corner stone of the program.The excitation of the glue that holds quarks and antiquarks closely together in mesons is predicted by the theory of strong interaction but has not experimentally been established. The GlueX experiment being constructed at JLab will be devoted to the search for such excitations. By using a high energy, highly polarized photon beam and a high-resolution detector with complete coverage, the GlueX experiment is expected to settle the question. CUA's contribution to the experiment is the construction and maintenance of the broad-band tagging hodoscope and the polarized photon source. The construction project provides excellent research opportunities for CUA's undergraduate students in physics and engineering who will be guided to take over key roles in prototyping, constructing and testing the hodoscope. The grant provided by NSF will support CUA's efforts in the frozen-spin target program in JLab's Hall B as well as the GlueX construction project.