: Construction of the first stage of the Pierre Auger Observatory has begun. The aim of the Observatory is to collect unprecedented information about cosmic rays above 10(18) eV. The first phase of the project, the construction and operation of a prototype system, known as the engineering array, has now been completed. It has allowed all of the sub-systems that will be used in the full instrument to be tested under field conditions. In this paper, the properties and performance of these sub-systems are described and their success illustrated with descriptions of some of the events recorded thus far. (C) 2003 Elsevier B.V

Keywords:Cosmic ray energy spectrum Cosmic ray composition The knee KASCADE Hadronic interaction models FLUKA GHEISHA a b s t r a c tThe KASCADE experiment measures extensive air showers induced by cosmic rays in the energy range around the so-called knee. The data of KASCADE have been used in a composition analysis showing the knee at 3-5 PeV to be caused by a steepening in the light-element spectra [T. Antoni et al., (KASCADE Coll.), Astropart. Phys. 24 (2005) 1-25]. Since the applied unfolding analysis depends crucially on simulations of air showers, different high-energy hadronic interaction models (QGSJet and SIBYLL) were used. The results have shown a strong dependence of the relative abundance of the individual mass groups on the underlying model. In this update of the analysis we apply the unfolding method with a different low energy interaction model (FLUKA instead of GHEISHA) in the simulations. While the resulting individual mass group spectra do not change significantly, the overall description of the measured data improves by using the FLUKA model. In addition data in a larger range of zenith angle are analysed. The new results are completely consistent, i.e. there is no hint to any severe problem in applying the unfolding analysis method to KASCADE data.

a b s t r a c t KASCADE-Grande is the enlargement of the KASCADE extensive air shower detector, realized to expand the cosmic ray studies from the previous 10 14 -10 17 eV primary energy range to 10 18 eV. This is performed by extending the area covered by the KASCADE electromagnetic array from 200 Â 200 to 700 Â 700 m 2 by means of 37 scintillator detector stations of 10 m 2 area each. This new array is namedGrande and provides measurements of the all-charged particle component of extensive air showers (N ch ), while the original KASCADE array particularly provides information on the muon content ðN m Þ. Additional dense compact detector set-ups being sensitive to energetic hadrons and muons are used for data consistency checks and calibration purposes. The performance of the Grande array and its integration into the entire experimental complex is discussed. It is demonstrated that the overall observable resolutions are adequate to meet the physical requirements of the measurements, i.e. primary energy spectrum and elemental composition studies in the primary cosmic ray energy range of 10 16-10 18 eV.

a b s t r a c tThe antenna array LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from extensive air showers. The coincident measurements allow us to reconstruct the electric field strength at observation level in dependence of general EAS parameters. In the present work, the lateral distribution of the radio signal in air showers is studied in detail. It is found that the lateral distributions of the electric field strengths in individual EAS can be described by an exponential function. For about 20% of the events a flattening towards the shower axis is observed, preferentially for showers with large inclination angle. The estimated scale parameters R 0 , describing the slope of the lateral profiles range between 100 and 200 m. No evidence for a direct correlation of R 0 with shower parameters like azimuth angle, geomagnetic angle, or primary energy can be found. This indicates that the lateral profile is an intrinsic property of the radio emission during the shower development which makes the radio detection technique suitable for large scale applications.

We observe a correlation between the slope of radio lateral distributions, and the mean muon pseudorapidity of 59 individual cosmic-ray-air-shower events. The radio lateral distributions are measured with LOPES, a digital radio interferometer co-located with the multi-detector-air-shower array KASCADE-Grande, which includes a muon-tracking detector. The result proves experimentally that radio measurements are sensitive to the longitudinal development of cosmic-ray air-showers. This is one of the main prerequisites for using radio arrays for ultra-high-energy particle physics and astrophysics.The investigation of ultra-high-energy cosmic rays works at the frontiers of particle physics as well as astrophysics. Only cosmic rays allow probing particle physics beyond the energy range of man-made accelerators. And only high statistics and accurate measurements of energy, direction and mass of cosmic rays will solve the mystery of their origin, i.e. how natural accelerators achieve energies beyond 10 20 eV (see references [1, 2] for reviews). Since ultra-high-energy cosmic rays are too rare to be measured directly, they can only be measured indirectly by observing extensive air-showers of secondary particles. In particular, the longitudinal development of the airshowers is of interest for the two main physics goals: for particle physics, since the shower development depends on the interactions at ultra-high energies, and for astro- *