Direct pair production by muons in medium and low Z elements

Abstract

The direct production of electron pairs by cosmic-ray muons (mean energy 6 GeV and minimum energy 0.85 GeV) in carbon, aluminium and copper targets of thicknesses 0.06, 0.14 and 0 44 radiation units, respectively, has been studied with two multi-plate cloud chambers. Showers of two or more electrons associated with each outgoing muon from the targets were selected, and the energy transfer in each event was estimated. The results, after necessary corrections, show that the experimental cross sections for direct pair production events in the region of energy transfers, 12 to 1000 MeV, are in approximate agreement with the theory of Murota-Ueda-Tanaka. They also support the expected Z(Z + 1) variations of the cross sections and the required variation with the mean primary muon energy. The data also indicate that the most appropriate value of the arbitrary parameter α in the Murota-Ueda-Tanaka theory is 2.