Measurements of the Lateral Distribution of the Muon Component of Extensive Air Showers Underground

The ALEPH detector at LEP has been supplemented with five scintillator stations to measure the muon component of cosmic ray showers underground. We report the measurements of coincidences over distances up to ab out 1 km which are sensitive to the forward production of hadronic interactions and the chemical composition of primary cosmic rays in the energy range around 10^15 eV. The results are compared to the expectations obtained from Monte Carlo simulation. Our results indicate that the observed decoherence curve of muons is compatible with a light primary composition. In addition, the arrival time of muons underground as measured with scintillator stations allow to reconstruct the muon arrival directions in 3-fold coincidence events. These results are compared to shower simulations.