The Lifetime Asymmetry of Polarized Muons in Flight
  Based on the parity violation in Standard Model, we study the dependence of the lifetime on the polarization of an initial-state fermion in weak interactions. The fermion lifetime was usually calculated in terms of spin states. However, after comparing spin states with helicity states and chirality states, it is pointed out that a spin state is helicity degenerate, and the spin state and the helicity state are entirely different. Using helicity states, we calculate the lifetime of polarized muons. The result shows that the lifetime of right-handed polarized muons is always greater than that of left-handed polarized muons with the same speed in flight. 
Zhi-Qiang Shi and Guang-Jiong Ni