The L3+C detector, a unique tool-set to study cosmic rays

The L3 detector at the CERN electron-positron collider, LEP, has been employed for the study of cosmic ray muons. The muon spectrometer of L3 consists of a set of high-precision drift chambers installed inside a magnet with a volume of about 1000 m**3 and a field of 0.5 T. Muon momenta are measured with a resolution of a few percent at 50 GeV. The detector is located under 30 m of overburden. A scintillator air shower array of 54 m by 30 m is installed on the roof of the surface hall above L3 in order to estimate the energy and the core position of the shower associated with a sample of detected muons. Thanks to the unique properties of the L3+C detector, muon research topics relevant to various current problems in cosmic ray and particle astrophysics can be studied.