MONTE-CARLO SIMULATION FOR MULTIPLE-MUON DISTRIBUTIONS OF COSMIC-RAYS

A high-multiplicity event detected by the Kolar Gold Field (KGF) detector is examined to determine whether or not it is an abnormal phenomenon, taking into account the cosmic-ray primary composition and ordinary interaction models. Our calculation shows that a proton-dominated primary composition around the "knee" is not consistent with measurements of the multiple-muon distributions. On the other hand, taking 15-40 % for the proton fraction and 25-50 % for iron nuclei, there is satisfactory agreement. We have estimated the frequency of multiple-muon events with muons in excess of 20 taking the above primary composition. From this result, one would expect such an event per 60-100 years of operation time, and therefore the probability of observing such an event becomes a few percent for the duration of KGF experiment. Thus, we would suppose that the KGF event is a natural phenomenon in spite of their argument that it is difficult to explain it in terms of a conventional muon production mechanism even if an extreme case of heavy chemical composition of primaries is assumed.