Measurements of the muon component of extensive air showers at 320m.w.e. underground

Abstract The ALEPH detector at LEP has been supplemented with five scintillator telescopes to measure the muon component of cosmic ray air showers underground. The emphasis of the present analysis of a new data set is to measure coincidences over distances up to about 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 1015 eV. First results indicate that the observed decoherence curve of muons is compatible with a light primary composition and the arrival directions of muons show no obvious clustering in galactic coordinates.