A Program to Study Hadronic Matter using Electromagnetic Probes at Jefferson Lab

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。该补助金的重点是支持我们在托马斯杰斐逊国家加速器设施（JLab）使用电磁探针在非常基础和基本的水平上研究强子物质的持续研究计划。 我们的团队在三个独立的实验中发挥了关键作用，这些实验测试了福尔斯“标准模型”的粒子相互作用的性质。其中一个实验Qweak利用弱相互作用的宇称破坏性质来测量标准模型的一个基本参数，即温伯格（或混合）角，相对误差在0.3%以内。这个角度与两个粒子的质量比有关，即W玻色子和Z玻色子，并且作为传递到散射目标的动量的函数而变化。这个实验的精确测量，当与其他实验相结合时，将对我们目前版本的标准模型的拟议扩展施加强有力的限制。在另一个实验中，我们小组的一名成员在杰斐逊实验室的B厅进行了π介子寿命测量，该实验旨在探索中性电荷π介子衰变为两个光子的机制。在这个实验中，中性π介子将通过普里马科夫效应从核的库仑场中光生，并将在高度分段的量热计中被检测到。该实验测量的基本量，可以计算的手征微扰理论的背景下，并代表了少数严格的实验测试QCD，可以在限制规模制度之一。我们的小组还进行了实验，从矢量介子光生与线性偏振光子在g8 B（质子）和g13 a/B（氘核）数据集，这是三个ISU博士论文的主题提取偏振观测。最近CLAS在光生和电生中提取单偏振和双偏振观测量的结果表明，它们对小的产生振幅具有很高的灵敏度，这是通过理解核子中夸克自由度的基本对称性，入射光子和目标核子之间的宇称交换性质，以及电磁反应中伴生奇异态的产生机理。作为JLab重子共振研究的自然延伸，我们希望将我们的研究扩展到北京正负电子对撞机，在那里我们将在北京电子谱仪（BES）上提取通过粲介子衰变的激发重子态。我们试图协调这项研究与北京谱仪通过分析的J/psi到重子-反重子通道，在那里我们期望探测核子共振（N*）的质量区域高达2 GeV的补充手段的衰减。我们的团队正计划在杰斐逊实验室的大厅B建造一套六个漂移室，用作区域1粒子跟踪系统。该小组在JLab的研究计划，ISU的加速器设施，以及探测器科学实验室的连续探测器建设项目，联合收割机结合在一个积极的计划中，提供了广泛的教育环境，可用于有效地培养下一代科学家的经验。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The focus of this grant goes towards supporting our continuing research program at the Thomas Jefferson National Accelerator Facility (JLab) using electromagnetic probes to study hadronic matter at the very fundamental and basic levels. Our group has taken crucial roles in three separate experiments that test the nature of particle interactions which falls under the rubric of the "Standard Model". One experiment, Qweak, uses the parity-violating property of the weak interaction to measure a fundamental parameter of the Standard Model known as the Weinberg (or mixing) angle to within a relative error of 0.3%. This angle is related to the ratio of two particle masses, the W and Z bosons, and varies as a function of the momentum transfered to the scattering target. A precise measurement from this experiment, when combined with other experiments, will place strong constraints on proposed extensions to our present version of the Standard Model. In another experiment, a member of our group leads the pion lifetime measurements undertaken in Jefferson Lab's Hall B which seeks to probe the mechanism through which a neutrally charged pion can decay into two photons. In this experiment, neutral pions will be photoproduced from the Coulomb field of nuclei via the Primakoff effect, and will be detected in a highly segmented calorimeter. The experiment measures a fundamental quantity which can be calculated in the context of chiral perturbation theory and represents one of the few stringent experimental tests of QCD that can be made in the confinement scale regime. Our group also conducts experiments to extract polarization observables from vector meson photoproduction with linearly-polarized photons in the g8b (proton) and g13a/b (deuteron) datasets, which is the subject of three ISU PhD theses. Recent CLAS results on the extraction of single- and double-polarization observables in photo- and electroproduction show their high sensitivity to small production amplitudes, which is key in extracting excited baryon state by affording an understanding of the underlying symmetry of the quark degrees of freedom in the nucleon, the nature of the parity exchange between the incident photon and the target nucleon, and the mechanism of associated strangeness production in electromagnetic reactions. As a natural extension to the JLab baryon resonance studies component at JLab, we expect to expand our research to the Beijing Electron Positron Collider, where we will extract excited baryons states decaying through charmed mesons at the Beijing Electron Spectrometer (BES). We seek to coordinate this research with BES by analyzing the decay of the J/psi into baryon-antibaryon channels, where we expect a complementary means for probing nucleon resonances (N*) in the mass region up to 2 GeV. Our group is planning to construct a set of six drift chambers to be used as the region 1 particle tracking system in Jefferson Lab's Hall B. This group's research program at JLab, the accelerator facilities at ISU, and continuous detector construction projects in the groups Laboratory for Detector Science, combine in an active program to provide a breadth of experiences in an educational environment which can be used to effectively train the next generation of scientists.