Research in Theoretical Hadronic Physics and Related Topics

这个理论项目将支持目前对粒子物理学标准模型之外的物理学的研究。 虽然标准模型已经成功地描述了构成宇宙中大部分已知物质的基本粒子，但许多问题仍然没有答案。 研究人员和他的合作者的理论计算将支持和建议对新物理特征敏感的低能实验的新途径。 一个突出的例子是质子半径之谜，其中使用电子测量质子半径给出了与使用μ子不同的结果。 PI将计算解释数据所需的修正，并将研究标准模型假设之外的问题，以解释质子半径之谜，沿着提出新的实验，以供将来测试这些想法。 另一个例子是用极化电子进行精确的电子-质子散射实验，其中PI将进行与初始实验扩展相关的计算，这些实验可能允许测量质子的短寿命激发态的特性，并将它们与基于当前理论理解的预测进行比较。 该项目将培养和支持博士后研究员和本科生。该项目的一个重点是寻找由于附近轨道μ子对核芯的极化而对μ子氦和μ子氘能级的修正。 需要精确的结果来评估测量的能级数据，并根据相对于使用电子的相应测量的半径差异来解释它。 另一个重点是计算在短寿命质子激发之一的Delta共振区域中极化电子散射的双光子修正。 为了研究作为一个实体本身的德尔塔，人们使用一个光子产生它，然后几乎立即通过第二个光子的进一步散射来测量它。 在这个项目中，PI将计算可靠地获得Delta介子的尺寸和磁性参数所需的精度要求。

This theoretical project will support current searches for physics beyond the Standard Model of particle physics. Although the Standard Model has been successful in describing the elementary particles that make up most of known matter in the Universe, many questions still remain unanswered. The theoretical calculations by the investigator and his collaborators will support and suggest new avenues for low-energy experiments sensitive for signatures of new physics. A prominent such example is the proton radius puzzle, where measuring the proton radius using electrons gives different results than using muons. The PI will calculate corrections needed for the interpretation of the data and will study beyond the Standard Model hypotheses to explain the proton radius puzzle, along with suggesting new experiments for future testing of these ideas. Another example is the case of precision electron-proton scattering experiments with polarized electrons, where the PI will do calculations relevant to extensions of the initial experiments that may allow measuring properties of short-lived excited states of the proton and the possibility of comparing them to predictions based on the current theoretical understanding of the physics involved. Postdoctoral fellows and undergraduates will be trained and supported by this project.One thrust of the project is to find corrections to the energy levels of muonic helium and deuterium due to the polarization of the nuclear cores by the near-by orbiting muons. Precise results are needed to evaluate the measured energy level data and interpret it in terms of radius discrepancies relative to corresponding measurements using electrons. Another thrust is to calculate two photon corrections to polarized electron scattering in the region where the Delta resonance, one of the short-lived proton excitations, exists. To study the Delta as an entity in itself, one produces it using one photon and then measures it almost immediately by a further scattering with a second photon. In this project, the PI will calculate the precision requirements needed to obtain reliably the size and magnetic parameters of the Delta meson.