The CosmoALEPH experiment, located underground at the LEP e+e?
storage ring at CERN at a depth of 320 m water equivalent, was used to study the chemical composition of primary cosmic rays up to 10 PeV energies from the measurement of high energy muons, created in extensive air showers by interactions of primary nuclei in the atmosphere.
The Time Projection Chamber (TPC) and the Hadron Calorimeter of the
ALEPH detector and six scintillator stations located at distances up to 1 km from each other were used to analyse the decoherence curve, multiplicity and transverse momentum distributions of energetic cosmic muons. The experimental data were compared with predictions from different Monte Carlo (MC) models and mass composition approaches.
From a comparison between the measured decoherence distribution with
CosmoALEPH and the MC predicted decoherence curves for proton, helium
and iron, a primary composition of (77±11) % protons and (23±11) % iron
nuclei with a ?2 - probability of 84 % was determined, based on the predictions of the VENUS model with the constant mass composition approach.
The analysis of the decoherence curve, with consideration of correlations between the measured CosmoALEPH parameters, leads to a composition of (88 ± 8) % protons and (12 ± 8) % iron nuclei for cosmic rays with a ?2 -probability of 53 %.
The absolute comparison between the measured multiplicity and transverse
momentum distributions in the TPC and those predicted by different
Monte Carlo models results also in a dominant light composition. The experimental data are in a good agreement with MC data lying between proton and helium primaries.
The results obtained for the primary composition of cosmic rays up to
the knee region are consistent with the results from other experiments.