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It has been shown that spectral statistics techniques, based on random matrix theory, can be applied to study correlations at ground level between the secondary particles of simulated extensive air showers. The statistical description of shower fronts provided by appropriate spectral measures makes it possible to separate them into different classes depending on the type of the primary cosmic ray. Using a suitable combination of spectral statistics in the framework of discriminant analysis, we introduce a new statistic which separates shower fronts according to the primary type with improved efficiency.

Spectral statistics techniques based on random matrix theory are applied to study the correlations at ground level among secondary particle density distributions of simulated extensive air showers. High-energy interactions of TeV cosmic γ -rays and protons with Earth atmosphere and the resulting extensive air showers have been simulated by means of the CORSIKA Monte Carlo code. The statistical description of shower fronts provided by this new type of analysis allows to distinguish events generated by primary protons from those initiated by primary γ -rays, and leads to a powerful discrimination method whose efficiency is evaluated using the standard quality factors.

High-energy interactions of cosmic rays with Earth atmosphere and the resulting extensive air showers have been simulated by means of the CORSIKA Monte Carlo code. Statistical fluctuations of the two-dimensional secondary Cerenkov photon density distributions at ground level produced by GeV cosmic γ rays and protons are studied by means of principal components analysis (PCA). This provides a decreasing sequence of covariance matrix eigenvalues that may be fitted to an analytical expression allowing to distinguish among different primary cosmic rays. A very efficient discrimination method of gamma ray induced showers from proton simulated extensive air showers is proposed as a result of this analysis. A cutting parameter is calculated, and the efficiency of the cutting procedure for γ–proton separation is evaluated under experimental conditions.

High-energy interactions of cosmic γ rays and protons with the earth atmosphere have been simulated by means of the CORSIKA Monte Carlo code, and the secondary particle density distributions at ground level in the resulting extensive air showers have been studied. It is shown that the power spectrum of the bidimensional particle density fluctuations have features typical of a 1/ f noise in the bidimensional frequency domain, and is found to have different features for different primary cosmic rays. This property is applied to the separation of electromagnetic from proton simulated extensive air showers and it is proposed as a new discrimination method that can be used experimentally for real-time γ–proton separation. A cutting parameter related to the bidimensional power spectrum is calculated and the efficiency of the cutting procedure for γ–proton separation is evaluated.

High-energy interactions of cosmic γ rays and protons and also helium, oxygen and iron nuclei with the Earth atmosphere have been simulated by means of the CORSIKA Monte Carlo code, and the secondary-particle density distributions at ground level in the resulting extensive air showers (EAS) have been studied. It is shown that the fluctuations of the particle density distributions have features typical of a 1/f noise. The multifractal spectrum of the samples is obtained and is found to have different features for different primary cosmic rays. This property is applied to the separation of electromagnetic from hadronic simulated EAS and it is proposed as a discrimination method when real data are available. A cutting parameter related to the multifractal spectrum is calculated and the efficiency of the cutting procedure for γ-hadron separation is evaluated.

A precise knowledge of the angular resolution of scintillator arrays used to observe extended air showers (EAS) is of key importance in the search for VHE/UHE γ point sources. Four independent methods have been used to determine the mean resolution for which a value of 〈ΔΘ63〉 of 0.8°(1.0°) at a proton threshold of 50 (40) TeV has been found for the HEGRA EAS-array.

The HEGRA collaboration has searched for γ-ray emission from 36 potential cosmic point sources with the wide angle air Cerenkov detector AIROBICC which is part of the HEGRA cosmic ray detector complex on La Palma. AIROBICC has a γ-ray energy threshold of around 24 TeV and a mean angular resolution of 0.29 °. None of the sources could be found. Upper limits to their fluxes are given. For the VHE γ-ray emitters, the Crab nebula and Mrk 421, these flux limits are below those extrapolated from lower energy observations. Our lower limit for Mrk 421 might be interpreted either as being due to an energy cut-off in the acceleration mechanism or to the onset of γ-interaction with photons of the universal infrared background.