# Relativistic Time Dilation in Muon Decay

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According to Einstein's special theory of relativity, a clock moving at a significant fraction of the speed of light with respect to an observer runs more slowly than the observer's own clock. This implies that time must be flowing more slowly in a moving frame of reference, which is referred to as *time dilation. *If a process (such as the decay of an unstable particle) occurs with an average lifetime of in the rest frame, the lifetime of the particle moving at speed is given by , where is the speed of light, 2.9979 × m/sec. The decay of muons has provided verification of Einstein's formula to a high degree of accuracy. The negative muon , with a mass of 105.7 MeV/, is the second-generation lepton analogous to the electron . The antiparticles and (the positron) are similarly related. The mean lifetime of free muon decay is 2.197 sec in the rest frame. The decay processes are and . Here is a neutrino and an antineutrino, each occurring in both electron and muon flavors. In finer detail, these weak-interaction processes involve bosons as intermediates.

Contributed by: S. M. Blinder (March 2011)

Correction by Howard Landman

Open content licensed under CC BY-NC-SA

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