HIGH-ENERGY COSMIC-RAY PHYSICS WITH UNDERGROUND MUONS IN MACRO .1. ANALYSIS-METHODS AND EXPERIMENTAL RESULTS

In this paper, the first of a two-part work, we present the reconstruc tion and measurement of muon events detected underground by the MACRO experiment at Gran Sasso (E-mu greater than or equal to 1.3 TeV in atm osphere). The main aim of this work is to discuss the muon multiplicit y distribution as measured in the detector. The data sample analyzed c onsists of 4.4 x 10(6) muon events, of which similar to 263 000 are mu ltiple muons, corresponding to a total live time of 5850 h. In this sa mple, the observed multiplicities extend above N-mu = 35, with intermu on separations up to 50 m and beyond. Additional complementing measure ments, such as the inclusive muon Aux, the angular distribution, and t he muon separation distribution (decoherence), are also included. The physical interpretation of the results presented here is reported in t he following companion paper.