TWIST - Precision measurement of muon decay parameters (TRIUMF E614)

TRIUMF弱相互作用对称性测试(TWIST)是一项寻找与非常成功的粒子相互作用标准模型预测的Muon衰变模式的微小偏差的测试。标准模型是一个多年来与许多观测结果相一致的理论，但大多数亚原子物理学家认为它只是一个更基本、更精确的模型的近似值，其性质尚不清楚。标准模型是不完整的，留下了几个问题没有回答，例如，为什么只有三代，为什么粒子有它们的质量？标准模型将最基本的粒子分为三代；只有第一代或最低一代的粒子构成了我们日常生活的材料。Muon是更高一代中最轻、最容易获得的基本带电粒子。它几乎总是衰变成一个电子和两个很轻的、难以捉摸的中性粒子，称为中微子。TRIUMF产生了高质量的µ子束，在高螺线管磁场中使用非常高精度的探测器系统来精确测量每一次数十亿次正衰变产生的正电子(或正电子)的方向和能量。这些衰变的模式或对称性是由标准模型准确预测的。如果发现与基于标准模型的预期的偏差，将为更基本地描述我们宇宙中最小粒子的特征提供线索。另一方面，如果没有发现偏差，则可以不考虑更基本描述的一些假设特征。

The TRIUMF Weak Interaction Symmetry Test (TWIST) is a search for tiny deviations from the pattern ofmuon decays predicted by the very successful Standard Model of particle interactions. The Standard Model, atheory which agrees with many observations over many years, is nonetheless believed by most subatomicphysicists to be only an approximation to a more basic and precise model whose properties are as yet notknown. The Standard Model is incomplete and leaves several questions unanswered, for example, why justthree generations, and why do the particles have the masses they do?The Standard Model classifies the most fundamental particles into three "generations"; only particles of thefirst or lowest generation make up the materials of our everyday lives. The muon is the lightest and mostaccessible fundamental charged particle of a higher generation. It nearly always decays into an electron and twovery light, elusive, neutral particles called neutrinos. High quality beams of muons are produced at TRIUMF,and a very high precision detector system in a high solenoidal magnetic field is used to accurately measure thedirection and energy of the positive electron (or positron) produced for each of billions of positive decays. Thepattern or symmetry of these decays is precisely predicted by the Standard Model.If found, a deviation from expectations based on the Standard Model would provide clues to the character of amore basic description of the smallest particles in our universe. On the other hand, if no deviation is found,some hypothesized features of a more basic description can be eliminated from consideration.