Cosmic multi-muon bundles measured at DELPHI

The DELPHI detector at LEP, located 100 $m$ underground, has been used to detect the multi-muon bundles by cathode readout of its hadron calorimeter and its tracking detectors (TPC, muon chambers). The experimental apparatus allows us to study muon bundles originating from primary cosmic particles with energies in the interval $10^{14}$ - $10^{17} eV$. The cosmic events registered during the years 1999 and 2000 correspond roughly to $1.6 10^6 s$ of effective run time. The aim of the work is to compare the measured muon multiplicity distributions and predictions of high energy interaction models for different types of primary particles and also to determine the absolute flux of events in certain muon multiplicity range. The presentation describes the current status of the analysis.Comment: 2 pages, 1 figure, presented at XXXVIIth Rencontres de Moriond Electroweak Interactions and Unified Theories 2002 (Young Scientists Forum

Detection of high-energy muons in cosmic ray showers

The DELPHI detector located at LEP accelerator has been used to measure multi-muon bundles originated from cosmic ray interactions. Two subdetectors - Hadron Calorimeter and Time Projection Chamber, are used for this purpose. The 1999 and 2000 data are analyzed over wide range of muon multiplicities. The muon multiplicity distribution is compared with prediction of Monte-Carlo simulation based on CORSIKA/QGSJET. The Monte-Carlo does not describe the large multiplicity part of data. Even the extreme assumption on the cosmic ray composition (pure iron nuclei) hardly predicts number of high multiplicity events comparable with the data. The impact of QGSJET internal parameters onto the result is also studied