Slow Mesons in the Cosmic Radiation

Abstract

The following experiment was performed to measure the disintegration time of cosmic-ray mesons. Mesons falling on a lead plate were detected by a layer of counters above the plate. Some of these mesons presumably stopped within the plate and a short time later emitted a disintegration electron and a neutrino. The electron would, in a certain fraction of the cases, be detected by a second layer of counters placed below the plate. Those events were recorded in which a discharge of one of the upper counters was followed by a discharge in one of the lower counters after a time $t_1$ and before a time $t_2$. In the absence of the lead plate, no disintegration electrons were expected. However, a considerable number of counter discharges were recorded which must be interpreted as the result of an intrinsic time delay in the counter between the passage of the ionizing ray, and an appreciable change in potential of the counter wire. The number of disintegration electrons was measured by taking the difference in the counting rates with the lead plate present and absent. For $t_1$ equal to 1.5 microseconds, and $t_2$ equal to 20 microseconds, we expected 23 electrons per hour, assuming that the mean life of the mestron is 2.7 microseconds. A series of observations results in the measured number of 1.4±2.4 per hour, a value much smaller than expected. Possible explanations of this discrepancy are discussed, the most likely one perhaps being that most mesons are absorbed by some nuclear process before they come to rest.