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

杰斐逊实验室使用电磁探针研究强子物质的计划

• 批准号: 0855661
• 负责人: Tony Forest
• 金额: $ 91万
• 依托单位: Idaho State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0855661&HistoricalAwards=false
• 关键词: Program; Study; Hadronic; Matter; using

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.

该奖项根据 2009 年《美国复苏和再投资法案》（公法 111-5）提供资助。这笔赠款的重点是支持我们在托马斯·杰斐逊国家加速器设施 (JLab) 的持续研究计划，使用电磁探测器在最基础和基础的层面上研究强子物质。 我们的小组在三个独立的实验中发挥了关键作用，这些实验测试了属于“标准模型”标题下的粒子相互作用的性质。一项名为 Qweak 的实验利用弱相互作用的宇称破坏特性来测量标准模型的基本参数（称为温伯格（或混合）角），相对误差在 0.3% 以内。该角度与两个粒子质量（W 和 Z 玻色子）的比率有关，并且随着传递到散射目标的动量的函数而变化。当与其他实验相结合时，该实验的精确测量将对我们当前版本的标准模型的拟议扩展产生严格的限制。在另一项实验中，我们小组的一名成员领导了在杰斐逊实验室 B 厅进行的 π 介子寿命测量，旨在探讨带中性电荷的 π 介子衰变成两个光子的机制。在该实验中，中性介子将通过普里马科夫效应从原子核的库仑场中光产生，并在高度分段的量热计中进行检测。该实验测量了一个可以在手性微扰理论背景下计算的基本量，并且代表了可以在限制尺度范围内进行的少数严格的 QCD 实验测试之一。我们小组还进行了实验，从 g8b（质子）和 g13a/b（氘核）数据集中的线性偏振光子的矢量介子光产生中提取偏振可观测量，这是三篇 ISU 博士论文的主题。最近 CLAS 在光和电产生中提取单偏振和双偏振可观测量的结果表明，它们对小产生幅度具有高敏感性，这是提取激发重子态的关键，通过提供对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宇称交换的性质以及电磁反应中相关奇异产生的机制的理解。作为 JLab 重子共振研究部分的自然延伸，我们希望将我们的研究扩展到北京正电子对撞机，在那里我们将在北京电子能谱仪 (BES) 中提取通过粲介子衰变的激发重子态。我们寻求通过分析 J/psi 进入重子-反重子通道的衰变来与 BES 协调这项研究，我们期望在高达 2 GeV 的质量区域中探测核子共振 (N*) 的补充方法。我们小组正计划在杰斐逊实验室 B 厅建造一组六个漂移室，用作区域 1 粒子跟踪系统。该小组在 JLab 的研究项目、ISU 的加速器设施以及小组探测器科学实验室的连续探测器建设项目，结合在一个积极的计划中，在教育环境中提供广泛的经验，可用于有效地培训下一代科学家。