Variation of the Rate of Decay of Mesotrons with Momentum

In order to determine the dependence of the probability of decay on momentum, mesotrons with range between 196 and 311 g/cm^2 of lead and mesotrons with range larger than 311 g/cm^2 of lead were investigated separately. The softer group of mesotrons was found to disintegrate at a rate about three times faster than the more penetrating group, in agreement with the theoretical predictions based on the relativity change in rate of a moving clock. A new value of the proper lifetime of mesotrons of (2. 40. 3) 10^-6 sec. is determined, based upon measurements with particles with momentum of approximately 510^8 ev/c.