Research in Intermediate Energy Physics

该项目涉及反映在介子和核子性质以及低/中能相互作用中的电弱和强相互作用的某些基本方面。 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变得不可行的强相互作用在低能量下。π介子（π）的罕见的β衰变，发生一次约1亿普通π介子衰变，提供了一个理论上干净的窗口，某些允许的扩展SM。 PIBETA实验由弗吉尼亚大学（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，旨在将目前的π介子β衰变率的4%精度提高约十倍，以便匹配理论不确定性并提供超越SM的物理学新约束。 1999年开始的测量将持续到2001年。 PIBETA是本研究项目的主要工作。 其他承诺的努力包括在斯坦福大学（SLAC）和杰斐逊实验室（CLAS合作）的核子和介子结构的研究工作。在过去的三年中，该计划导致了两个博士学位在弗吉尼亚大学和三个以上的合作大学源于PIBETA项目。 又有四个弗吉尼亚大学的博士预计在未来三到四年内， 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。

This project addresses certain fundamental aspects of the electroweakand strong interactions that are reflected in meson and nucleonproperties and interactions at low/intermediate energies. Theresearch is motivated by the fact that the present comprehensivetheory--the Standard Model (SM)--is known to be incomplete;furthermore, the SM becomes unworkable for strong interactions at lowenergies.The rare beta decay of the pi-meson (pion), occurring once in about100 million ordinary pion decays, provides a theoretically cleanwindow to certain allowed extensions of the SM. The PIBETAexperiment, mounted at the Paul Scherrer Institute, Switzerland, by aninternational collaboration of seven institutions led by theUniversity of Virginia (UVa) group, aims to improve the present 4%accuracy of the pion beta decay rate by about a factor of ten in astaged approach, in order to match the theoretical uncertainty andprovide new constraints on physics beyond the SM. Measurements thatbegan in 1999 will continue through 2001. PIBETA is the main effortof the present research project. Additional commitments of effortinclude work on studies of nucleon and meson structure at Stanford(SLAC) and Jefferson Lab (CLAS collaboration).During the past three years this program has resulted in two doctoraldegrees at UVa plus three more at collaborating universities stemmingfrom the PIBETA project alone. Four more UVa Ph.D. degrees areexpected in the next three to four years. Each year typically one totwo undergraduate students are engaged in research on this project,thus gaining practical laboratory experience.