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Different interaction models treating hadronic collisions below in air shower simulations are compared within the frame of the CORSIKA program. Their behaviour is studied in isolated collisions of protons or pions with light-mass targets in comparison with experimental data. It is discussed how model properties influence air-shower parameters like the longitudinal profile or the lateral distribution of particles arriving at ground. [Copyright &y& Elsevier]

Collider data covering the very forward directions at the highest attainable energies are most important for improving high-energy hadronic interaction models which are used in extensive air shower simulation programs like CORSIKA. [Copyright &y& Elsevier]

The three hadronic interaction models DPMJET 2.55, QGSJET 01, and SIBYLL 2.1, implemented in the air shower simulation program CORSIKA, are compared in the energy range of interest for the Pierre Auger experiment. The model dependence of relevant quantities in individual hadronic interactions and air showers is investigated. [Copyright &y& Elsevier]

Using the correlations of the hadronic, electromagnetic, and muonic components of extensive air showers measured with the experiment KASCADE the influence of hadronic interaction models on the simulation of air showers is investigated. For the simulations CORSIKA with GHEISHA and FLUKA as low-energy models and DPMJET, SIBYLL, and QGSJET as high-energy models have been used. [Copyright &y& Elsevier]

Directional information on air showers from the KASCADE Array and on muons registered in the Muon Tracking Detector (MTD) allow to investigate pseudorapidity and momentum distributions of muons. The possibility to test hadronic interaction models, to study primary mass composition and parameters of hadronic interactions with these distributions is discussed. [Copyright &y& Elsevier]

KASCADE is a multi-detector setup to get redundant information on single air shower basis. The information is used to perform multiparameter analyses to solve the threefold problem of the reconstruction of (i) the unknown primary energy, (ii) the primary mass, and (iii) to quantify the characteristics of the hadronic interactions in the air-shower development. In this talk recent results of the KASCADE data analyses are summarized concerning cosmic ray anisotropy studies, determination of flux spectra for different primary mass groups, and approaches to test hadronic interaction models. Neither large scale anisotropies nor point sources were found in the KASCADE data set. The energy spectra of the light element groups result in a knee-like bending and a steepening above the knee. The topology of the individual knee positions shows a dependency on the primary particle. Though no hadronic interaction model is fully able to describe the multi-parameter data of KASCADE consistently, the more recent models or improved versions of older models reproduce the data better than few years ago. [Copyright &y& Elsevier]

A hybrid simulation code is developed that is suited for fast one-dimensional simulations of shower profiles, including fluctuations. It combines the Monte Carlo simulation of high energy interactions with a fast numerical solution of cascade equations for the resulting distributions of secondary particles. Results obtained with this new code, called conex, are presented and compared to corsika predictions. [Copyright &y& Elsevier]

Recent results of the KASCADE air shower experiment are presented, in order to shed some light on the astrophysics of cosmic rays in the region of the knee in the energy spectrum. The results include investigations of high-energy interactions in the atmosphere, the analysis of the arrival directions of cosmic rays, the determination of the mean logarithmic mass, and the unfolding of energy spectra for elemental groups. [Copyright &y& Elsevier]

Recent results from the KASCADE experiment on measurements of cosmic rays in the energy range of the knee are presented. Emphasis is placed on energy spectra of individual mass groups as obtained from an two-dimensional unfolding applied to the reconstructed electron and truncated muon numbers of each individual EAS. The data show a knee-like structure in the energy spectra of light primaries (p, He, C) and an increasing dominance of heavy ones (A ≳ 20) towards higher energies. This basic result is robust against uncertainties of the applied interaction models QGSJET and SIBYLL which are used in the shower simulations to analyse the data. Slight differences observed between experimental data and EAS simulations provide important clues for further improvements of the interaction models. The data are complemented by new limits on global anisotropies in the arrival directions of CRs and by upper limits on point sources. Astrophysical implications for discriminating models of maximum acceleration energy vs galactic diffusion/drift models of the knee are discussed based on this data. [Copyright &y& Elsevier]

The KASCADE experiment measures local muon densities of air-showers in the knee region at various core distances for two different muon energy thresholds. Muon density spectra have been reconstructed for the total EAS sample, as well as for particular subsamples with enhanced light and heavy induced EAS, classified on the basis of the shower size ratio Nμ/Ne. By comparing these spectra for different muon energy detection thresholds and core distances with detailed Monte Carlo simulations each spectrum should result in the same primary energy spectrum. This allows a comprehensive test of the simulation procedures of the muon lateral distribution and the muon energy spectrum by various Monte Carlo codes. Different combinations of high-energy and low-energy interaction models in the frame of the CORSIKA code are used for comparisons. [Copyright &y& Elsevier]

The interpretation of extensive air shower measurements often requires the comparison with EAS simulations. These calculations rely on hadronic interaction models which have to extrapolate into kinematical and energy regions not covered by present-day collider experiments. The KASCADE experiment with its large hadron calorimeter and its detectors for the electromagnetic and muonic components provides experimental data to check hadronic interaction models. For the EAS simulations the program CORSIKA with several hadronic event generators embedded is used. Different hadronic observables are investigated as well as their correlations with the electromagnetic and muonic components. Comparing the interaction models QGSJET 98, NEXUS II, and DPMJET 11.5, it is found, that QGSJET describes the data best. [Copyright &y& Elsevier]

The field detector array of the KASCADE experiment measures the electron and muon component of extensive air showers in the knee region with high precision. A baysian unfolding procedure is presented in which the two-dimensional shower size distribution (Ne, Nμtr) is examined. On the arbitrary assumption that the chemical composition consists of five primary mass groups (hydrogen, helium, carbon, silicon and iron) the size distribution is deconvoluted to reconstruct the energy spectra of these mass groups in the energy range between 1015 eV and 1017 eV. The energy spectra of the lighter element groups result in a knee-like bending with a steepening above the knee. The topology of the individual knee positions suggest a rigidity dependence. [Copyright &y& Elsevier]

Muon production heights in EAS provide a specific tool to investigate the longitudinal development of EAS, since muons are little affected by subsequent interactions in the atmosphere. Multiplicity of muons presents also a unique tool to investigate hadronic interaction models. The capability of the Muon Tracking Detector to measure radial and tangential angles of muon tracks in EAS, in combination with the shower direction determined by the Array of the KASCADE experiment, has been investigated. Due to different characteristics in shower development of light and heavy primary cosmic ray particles the radial angle and therefore the related production height is sensitive to the mass of them. Muon production height (MPH) and muon production depth (MPD) were studied in different bins of the muon shower size for measured data and MC simulations, which have been performed using the Monte Carlo program CORSIKA with the hadronic interaction models QGSJet and neXus. First composition studies on the basis of MPD distributions have been carried out. [Copyright &y& Elsevier]

Using the facilities of the KASCADE Central Detector EAS muon arrival time distributions, observed with reference to the arrival time of the first locally registered muon, and their correlations with other EAS observables have been investigated at different distances Rμ from the shower axis. Invoking detailed Monte Carlo simulations non-parametric multivariate even-by-event analyses have been performed for an estimate of the primary mass composition. The consistency of the Monte Carlo simulations is studied by comparing the primary mass composition results inferred from observations at different Rμ and different muon multiplicity thresholds nth. [Copyright &y& Elsevier]

The key observables of the KASCADE field array are the electron and muon number of extensive air showers. Using the size spectra of these measured quantities and their correlations with energy and primary mass it is possible to reconstruct the energy spectra of individual mass groups. The analysis relies on the application of unfolding methods. The resulting spectra of the light components show a knee-like feature. The positions of the individual knees suggest a dependence on the primary charge even if the statistical and systematical significance has to be improved. [Copyright &y& Elsevier]

The longitudinal profile of the 320 EeV event observed by the Fly''s Eye experiment is analysed. A method of testing the hypothesis of a specific primary particle type is described. Results for different particle types are summarized. For hadronic primaries between proton and iron nuclei, the discrepancy between observed and simulated profiles is in the range of 0.6-1.0σ for two different hadronic interaction models investigated. For primary photons, the discrepancy is 1.5σ assuming a standard extrapolation of the photonuclear cross-section with energy. Larger values of the cross-section at highest energies make primary photon showers more similar to hadron-initiated events. The influence of varying the extrapolation of the photonuclear cross-section is studied. [Copyright &y& Elsevier]

In this work the ultra high energy cosmic ray events recorded by the AGASA experiment are analyzed. With detailed simulations of the extensive air showers initiated by photons, the probabilities are determined of the photonic origin of the 6 AGASA events for which the muon densities were measured and the reconstructed energies exceeded 1020 eV. On this basis a new, preliminary upper limit on the photon fraction in cosmic rays above 1020 eV is derived and compared to the predictions of exemplary top-down cosmic-ray origin models. [Copyright &y& Elsevier]

The new, publicly available Monte Carlo program PRESHOWER is presented. It allows detailed studies on conversion and cascading of UHE photons in the geomagnetic field. When coupled to a standard air shower simulation program, PRESHOWER enables complete simulations of UHE photon-induced showers. [Copyright &y& Elsevier]