J. Scholz

KASCADE measurements of energy spectra for elemental groups of cosmic rays: Results and open problems

Abstract A composition analysis of KASCADE air shower data is performed by means of unfolding the two-dimensional frequency spectrum of electron and muon numbers. Aim of the analysis is the determination of energy spectra for elemental groups representing the chemical composition of primary cosmic rays. Since such an analysis depends crucially on simulations of air showers the two different hadronic interaction models QGSJet and SIBYLL are used for their generation. The resulting primary energy spectra show that the knee in the all particle spectrum is due to a steepening of the spectra of light elements but, also, that neither of the two simulation sets is able to describe the measured data consistently over the whole energy range with discrepancies appearing in different energy regions.

The cosmic-ray experiment KASCADE

KASCADE has been designed to measure air showers of primary cosmic-ray energies in the PeV region and to investigate the knee phenomenon in the all-particle energy spectrum. Several observations are measured simultaneously for each event by different detector systems. The experiment started to take data in 1996 and has been completed and extended since then. The individual detector systems and their performances are described. Also, the experience in long-term operation of the experiment and the interplay between different components is outlined.

Large-Scale Cosmic-Ray Anisotropy with KASCADE

We present the results of an analysis of the large-scale anisotropy of cosmic rays in the PeV range. The Rayleigh formalism is applied to the right ascension distribution of extensive air showers measured by the KASCADE (Karlsruhe Shower Core and Array Detector) experiment. The data set contains about 108 extensive air showers in the energy range 0.7-6 PeV. No hints of anisotropy are visible in the right ascension distributions in this energy range. This accounts for all showers, as well as for subsets containing showers induced by predominantly light or heavy primary particles, respectively. Upper flux limits for Rayleigh amplitudes are determined to be between 10-3 at a primary energy of 0.7 PeV and 10-2 at 6 PeV.

A non-parametric approach to infer the energy spectrum and the mass composition of cosmic rays

Abstract The experiment KASCADE observes simultaneously the electron–photon, muon, and hadron components of high-energy extensive air showers (EAS). The analysis of EAS observables for an estimate of energy and mass of the primary particle invokes extensive Monte Carlo simulations of the EAS development for preparing reference patterns. The present studies utilize the air shower simulation code corsika with the hadronic interaction models VENUS, QGSJet and Sibyll, including simulations of the detector response and efficiency. By applying non-parametric techniques the measured data have been analyzed in an event-by-event mode and the mass and energy of the EAS inducing particles are reconstructed. Special emphasis is given to methodical limitations and the dependence of the results on the hadronic interaction model used. The results obtained from KASCADE data reproduce the knee in the primary spectrum, but reveal a strong model dependence. Owing to the systematic uncertainties introduced by the hadronic interaction models no strong change of chemical composition can be claimed in the energy range around the knee.

Muon density measurements with the KASCADE central detector

Abstract Frequency distributions of local muon densities in high-energy extensive air showers (EAS) are presented as signature of the primary cosmic ray energy spectrum in the knee region. Together with the gross shower variables like shower core position, angle of incidence, and the shower sizes, the KASCADE experiment is able to measure local muon densities for two different muon energy thresholds. The spectra have been reconstructed for various core distances, as well as for particular subsamples, classified on the basis of the shower size ratio N μ / N e . The measured density spectra of the total sample exhibit clear kinks reflecting the knee of the primary energy spectrum. While relatively sharp changes of the slopes are observed in the spectrum of EAS with small values of the shower size ratio, no such feature is detected at EAS of large N μ / N e ratio in the energy range of 1–10 PeV. Comparing the spectra for various thresholds and core distances with detailed Monte Carlo simulations the validity of EAS simulations is discussed.

Search for Cosmic-Ray Point Sources with KASCADE

A survey of the northern hemisphere for astrophysical point sources with continuous emission of high-energy cosmic rays is presented. Around 4.7 × 107 extensive air showers with primary energies above ≈300 TeV measured by the KASCADE detector field are selected for this analysis. Besides the sky survey, a search for signal excess in the regions of the Galactic plane and of selected point-source candidates has been performed. There is no evidence for any significant excess. This is valid for an analysis of all recorded showers, as well as for a data set enhanced by γ-ray-induced showers. An upper flux limit of around 3 × 10-10 m-2 s-1 for a steady point source that transits the zenith is obtained. Additionally, the distribution of the arrival directions of extensive air showers with energies above 80 PeV was studied by an autocorrelation analysis.

The primary proton spectrum of cosmic rays measured with single hadrons at ground level

The flux of cosmic-ray‐induced single hadrons near sea level has been measured with the large hadron calorimeter of the KASCADE experiment. The measurement corroborates former results obtained with detectors of smaller size if the enlarged veto of the 304 m 2 calorimeter surface is accounted for. The program CORSIKA/ QGSJET is used to compute the cosmic-ray flux above the atmosphere. Between E0 ¼ 300 GeV and 1 PeV the primaryprotonspectrumcanbedescribedwithapowerlawparameterizedasdJ =dE0 ¼ (0:15 � 0:03)E � 2:78� 0:03 0 m � 2 s � 1 sr � 1 TeV � 1 . At the lower energy end the proton flux compares well with the results from recent direct measurements. Subject headingg cosmic rays

Test of hadronic interaction models in the forward region with KASCADE event rates

An analysis of muon and hadron rates observed in the central detector of the KASCADE experiment has been carried out. The data are compared with CORSIKA simulations employing the high-energy hadronic interaction models QGSJET, DPMJET, HDPM, SIBYLL and VENUS. In addition, first results with the new hadronic interaction model neXus 2 are discussed. Differences of the model predictions, both among each other and when confronted with measurements, are observed. The hadron rates mainly depend on the inelastic cross section and on the contribution of diffraction dissociation. The discrepancy between simulations and measurements at low primary energies

Measurements of attenuation and absorption lengths with the KASCADE experiment

Abstract The attenuation of the electron shower size beyond the shower maximum is studied with the KASCADE extensive air shower (EAS) experiment in the primary energy range of about 10 14 –10 16 eV. Attenuation and absorption lengths are determined by applying different approaches, including the method of constant intensity, the decrease of the flux of EASs with increasing zenith angle, and its variation with ground pressure. We observe a significant dependence of the results on the applied method. The determined values of the attenuation length ranges from 175 to 196 g/cm 2 and of the absorption length from 100 to 120 g/cm 2 . The origin of these differences is discussed emphasizing the influence of intrinsic shower fluctuations.

KASCADE: Astrophysical results and tests of hadronic interaction models

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.