Production Cross Section and Frequency of Neutral Mesons in Cosmic Rays

Nuclear interactions have been observed in a large cloud chamber operated at Echo Lake, Colorado, altitude 10,500 ft. The events were produced by ionizing particles (protons) in NaI crystals inside the cloud chamber, and were detected by photomultipliers.In this paper the electromagnetic component associated with the nuclear events is studied as evidence for the properties of the neutral meson whose decay is assumed to be the source of this component. The results are consistent with the assumption that the π⁰ mesons are the main source of the photons associated with the nuclear events. The probability of production of π⁰ mesons is in agreement with the theoretical results of Fermi, within the limits of the large experimental errors. The ratio of the number of neutral π⁰ mesons to the number of the charged π^± mesons is estimated in events of different multiplicities of shower particles and it is found to be close to 0.5 for events with multiplicity varying from 1 to 5 or more (corresponding to energies of from 1 to about 20 Bev for the producing protons).These results agree with the results of other experimenters, if all the possible systematic errors are taken into account. The estimated energy distribution of the π⁰ mesons emitted is given.