Precision Measurements in Intermediate Energy Physics

我们的研究主要集中在亚原子粒子μ子的性质上。 μ子很容易在粒子加速器中产生，它们是地球表面宇宙射线的主要成分。 根据所有的实验证据，它们和电子一样，只是重200倍，而且具有放射性。 μ子存在的原因是一个很大的谜。和电子一样，μ子可以被认为是一个绕轴旋转的球体。它也是一块磁铁，北极沿着转轴指向。多年来，我们一直在做一个实验，以非常高的精度测量这种磁铁的强度。 这个量的值对粒子的光谱非常敏感;如果有新的、尚未见过的粒子，那么该值将与理论预期不同。 我们已经看到了一个偏离预期值的现象，这很有趣，但还不足以成为新物理学的证据。 我们正在提出进一步的测量，以加强理论和实验之间的比较。与此同时，我们正在进行一些重要的实验来研究μ子的其他参数：它的寿命，它的电偶极矩，以及它在没有通常伴随的中微子的情况下直接衰变为电子的可能性。 最后一个过程从未被观察到，预计非常罕见。 寿命实验正在进行中，而其他两个实验正在开发中。

Our research is centered on the study of the properties of subatomicparticles called muons. Muons are easily produced at particleaccelerators, and they are a major component of cosmic rays at thesurface of the earth. According to all experimental evidence they arethe same as electrons except that they are 200 times heavier, and theyare radioactive. It is a great mystery why muons exist at all.Like the electron, the muon can be thought of as a sphere which spins onits axis. It is also a magnet, with the north pole pointing along thespin axis. For a number of years, we have been doing an experiment tomeasure the strength of this magnet to very high precision. The valueof this quantity is very sensitive to the spectrum of particles; ifthere are new, as yet unseen particles, then the value will be alteredfrom theoretical expectations. We have seen a deviation from theexpected value which is interesting but not yet big enough to beconvincing evidence of new physics. We are proposing furthermeasurements to sharpen the comparison between theory and experiment. At the same time, we are mounting major experiments to investigate otherparameters of the muon: its lifetime, its electric dipole moment, andthe probablility that it will decay directly into an electron withoutthe usual accompanying neutrino. The last process has never beenobserved, and is expected to be very rare. The lifetime experiment iswell under way, while the other two experiments are in development.