Violations of Einstein's time dilation formula in particle decays
  A rigorous quantum relativistic approach has been used to calculate the relationship between the decay laws of an unstable particle seen from two inertial frames moving with respect to each other. In agreement with experiment, it is found that the usual Einstein's time dilation formula is rather accurate in this case. However, small corrections to this formula were also obtained. Although the observation of these corrections is beyond the resolution of modern experiments, their presence indicates that special relativistic time dilation is not rigorously applicable to particle decays. 
Eugene V. Stefanovich