Research in Intermediate Energy Physics

* 9804708 Pocanic这个项目解决了某些基本方面，特别是对称性，反映在介子和核子的性质，结构和相互作用在低/中能的电弱和强相互作用。这项研究的动机是，目前的综合理论-标准模型（SM）-是已知的是不完整的;此外，SM成为在低能量强相互作用不可行的。 π介子（π介子）的罕见β衰变，大约在1亿次普通π介子衰变中发生一次，为SM的某些允许扩展提供了理论上干净的窗口。 PIBETA实验由UVa小组领导的七个机构的国际合作在瑞士保罗谢勒研究所进行，旨在通过分阶段方法将目前的4%精度提高到10倍以上，以匹配理论不确定性并提供新的物理学约束超越SM。 测量工作将于1998年夏季开始，并将持续数年。 PIBETA是本研究提案的主要努力。 其他承诺的努力包括在斯坦福大学（SLAC实验E155）和杰斐逊实验室（CLAS和RADPHI合作）研究核子和介子结构的工作。 最后，该小组关于π介子-π介子和π介子-核子系统中手征对称性破缺的工作正在完成并发表。（手征对称性是低能强相互作用的组织原则。 在过去的四年中，该计划导致了两个博士和一个硕士学位在弗吉尼亚大学。 两个弗吉尼亚大学的博士预计在未来三年内将有300多个学位获得，另外，仅PIBETA项目就将在合作大学增加三个学位。 每年通常有一到两名本科生参与该项目的研究，从而获得实际的实验室经验。

***9804708PocanicThis project addresses certain fundamental aspects, especially symmetries, of the electroweak and strong interactions that are reflected in meson and nucleon properties, structure and interactions at low/intermediate energies. This research is motivated by the fact that the present comprehensive theory--the Standard Model (SM)--is known to be incomplete; furthermore, the SM becomes unworkable for strong interactions at low energies. The rare beta decay of the pi-meson (pion), occurring once in about 100 million ordinary pion decays, provides a theoretically clean window to certain allowed extensions of the SM. The PIBETA experiment, mounted at the Paul Scherrer Institute, Switzerland, by an international collaboration of seven institutions led by the UVa group, aims to improve the present 4% accuracy of the pion beta decay rate by better than a factor of ten in a staged approach, in order to match the theoretical uncertainty and provide new constraints on physics beyond the SM. Measurements will begin in the summer of 1998 and will continue for several years. PIBETA is the main effort of the present research proposal. Additional commitments of effort include work on studies of nucleon and meson structure at Stanford (SLAC experiment E155) and Jefferson Lab (CLAS and RADPHI collaborations). Lastly, this group's work on chiral symmetry breaking in the pion-pion and pion-nucleon systems is being completed and published. (Chiral symmetry is the organizing principle in low-energy strong interactions.) During the past four years this program has resulted in two doctoral and one master's degree at UVa. Two more UVa Ph.D. degrees are expected in the next three years, plus three more at collaborating universities stemming from the PIBETA project alone. Each year typically one to two undergraduate students are engaged in research on this project, thus gaining practical laboratory experience.***