Calculation of high-energy muon interaction in Akeno calorimeter

Monte Carlo simulation is carried out for electromagnetic interaction of highenergy muons in a calorimeter, which is considered to be responsible for the background observed in the monopole search experiments performed in the observatory in Akino, Yamanashi Prefecture, Japan. The processes taken into consideration in this study are (1) direct pair production, (2) bremsstrahlung, (3) knockon electron ejection and (4) ionization loss. Relations between the average number of interactions and the muon energy are shown and simulated results on high-energy muon in the model calorimeter are presented. The simulated events to some extent seems to agree qualitatively with those actually measured. It is inferred from the simulated results that the small shower which is seen in analyzing monopole experiment results is caused by high-energy muons (≥ 1 TeV). However, the number of events simulated in the present study corresponds to only 2 x 10-8 cm-2S-1, i.e., events which may occur over an area of 50 m2 during a time period as short as two minutes. Considering this, it seems almost impossible to reproduce the 'rather narrow shower' which may remain until the last steps of the analysis. The major problem in the actual operation is the fact that too much CPU time is required for the computer calculation. (Nogami, K.)