Investigation of cosmic ray muons with the WILLI detector compared with the predictions of theoretical models and with semi-analytical formulae

The WILLI detector, built in IFIN-HH, Bucharest, is used to measure the muon flux and the muon charge ratio at low energy (< 1 GeV/c). The results are compared with detailed Monte-Carlo simulations performed with the CORSIKA code which takes into account the influence of the geomagnetic field. Two different hadronic interaction models (DPMJET and QGSJET) are used for the simulations. The semi-analytical formulae of Nash and Gaisser are also compared with experimental data and with Monte-Carlo simulations using DPMJET model. An investigation of the azimuth and zenithal variation of the muon flux is performed. Good agreement between the simulations and the experimental data is reported. The comparison between the simulations using DPMJET and QGSJET models indicates only small differences between them. To check the hadronic interaction models for high energy interactions, new experimental facilities are under developement for getting new experimental data.