NSF-BSF: The Study of Nuclear Physics with Intermediate Energy Probes

虽然普通物质98%的质量是由于强大的亚原子力，但目前关于这种力的理论(量子色动力学)仍然没有完全被理解。该奖项支持通过在弗吉尼亚州纽波特纽斯的托马斯·杰斐逊国家加速器设施(JLab)和瑞士的保罗·谢勒研究所(PSI)通过实验探索物质的亚结构来研究强力。这项研究有助于解决用夸克和胶子成分来描述中子和质子的主要问题，当两个或三个物体存在于其他介质中时产生的相互作用，密集核物质的性质，以及核子结构。回答这些和相关的问题是一项复杂的任务，需要专心的实验观测和仔细的理论预测与测量观测相对照的测试，这是本项目的目标。这项研究将有助于发现和增进对核物理的理解，并将促进教学、培训和学习。南卡罗来纳大学(UofSC)的核物理研究项目设在弗吉尼亚州纽波特纽斯的托马斯·杰斐逊国家加速器设施(JLab)和瑞士的保罗·谢勒研究所(PSI)。在PSI，该小组正在进行缪斯实验，该实验将解决同时测量带有正负电荷轻子的电子-质子和µ子-质子弹性截面中的质子半径之谜。这四组数据中的每一组都将允许提取质子电荷半径。结合起来，这些数据测试了电子和Muon相互作用以及额外的双光子交换效应之间可能存在的差异。该小组在JLab的计划将继续提供至关重要的高精度、偏振和非偏振的观测数据，这些观测数据将解决目前在强QCD中存在的问题。弹性和跃迁形状因子将跟踪从介子重子到修饰夸克自由度的演化，建立早熟标度的早期开始，这进一步体现了重子的三夸克结构，并解决了动力学质量产生和约束问题。双体和三体超子核子力对理解中子星的性质至关重要，而双体超子核子力和三体超子核子力是理解中子星性质的基础。用来直接估算J/ψ-N截面的J/ψ-N光生电子截面，可以让我们第一次一窥氘核的胶子结构。完成介子-光产生测量将以一种几乎与模型无关的方式解决N*物理中挥之不去的问题，并验证SU(6)×O(3)预测的三夸克重子结构。强子的性质在介质中被改变，束缚质子的电磁形状因子可能与真空中的不同，正如该小组早期的测量首次揭示的那样。分别在Mami和JLab进行的核目标实验将证实或驳斥这些结果。对这种现象的观察可能会改变我们如何看待强子及其在核问题上的相互作用。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Although ninety-eight percent of the mass of ordinary matter is due to the strong subatomic force, the present theory of that force (Quantum Chromodynamics) is still not fully understood. This award supports the study of the strong force by probing the substructure of matter through experiments at the Thomas Jefferson National Accelerator Facility (JLab) in Newport News, Virginia, and the Paul Scherrer Institute (PSI) in Switzerland. The research helps to address overarching questions about describing neutrons and protons in terms of their quark and gluon constituents, interactions that arise when two or three bodies are present in other media, the properties of dense nuclear matter, and the structure of nucleons. Answering these and related questions is a complex task that requires the dedicated experimental observations and careful testing of theoretical predictions against measured observations that are the goal of this project. This research will help discovery in and advance understanding of nuclear physics, and will promote teaching, training, and learning. The preparation of junior scientists plays a central role in the supported activities.The nuclear physics research program at the University of South Carolina (UofSC) is based at the Thomas Jefferson National Accelerator Facility (JLab) in Newport News, Virginia, and the Paul Scherrer Institute (PSI) in Switzerland. At PSI, the group is performing the MUSE experiment, which will address the proton-radius puzzle in simultaneous measurements of the electron-proton and muon-proton elastic cross sections with positively and negatively charged leptons. Each of the four sets of data will allow the extraction of the proton charge radius. In combination, the data test possible differences between the electron and muon interactions and additionally two-photon exchange effects. The group’s program at JLab will continue to provide crucial high precision, polarized and unpolarized observables that will address present problems in strong QCD. The elastic and transition form-factor will trace the evolution from meson baryon to dressed-quark degrees of freedom, establish the early onset of precocious scaling that further manifests the three-quark structure of baryons, and address the dynamical mass generation and confinement problem. The cross-sections for lambda deuteron elastic scattering will provide new and independent constraints on the two- and three-body hyperon-nucleon force, which is essential to understand the properties of neutron stars. The cross-sections for J/ψ photoproduction off the deuteron will give a direct estimate of the J/ψ-N cross-section and a very first glimpse into the gluon structure of deuterons. Completing meson-photoproduction measurements will settle in an almost model-independent way lingering problems in N* physics and verify the SU(6)×O(3)-predicted three-quark baryon structure. The properties of hadrons are modified in the medium and bound proton electromagnetic form factors may differ from those in the vacuum, as revealed for the first time by the group's earlier measurements. The experiments on nuclear targets at MAMI and JLab, respectively, will confirm or refute these results. The observations of such phenomena are potentially transformative in how we view hadrons and their interactions in nuclear matter.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.