F. Feßler

Bio: F. Feßler is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: KASCADE & Air shower. The author has an hindex of 14, co-authored 46 publications receiving 1557 citations.

The cosmic-ray experiment KASCADE

Abstract: 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.

Electron, Muon, and Hadron Lateral Distributions Measured in Air-Showers by the

Abstract: eV and extend from the inner coreregion to distances of 200 m. The electron and muon distributions are correctedfor mutual contaminations by taking into account the detector properties in theexperiment. All distributions are well described by NKG-functions. The scale radiidescribing the electron and hadron data best are ≃ 30 m and ≃ 10 m, respectively.We discuss the correlation between scale radii and ‘age’ parameter as well as theirdependence on shower size, zenith angle, and particle energy threshold.Key words: cosmic rays; air shower; lateral distributionPACS: 96.40.Pq

Test of high-energy interaction models using the hadronic core of EAS

Abstract: Using the large hadron calorimeter of the KASCADE experiment, hadronic cores of extensive air showers have been studied The hadron lateral and energy distributions have been investigated in order to study the reliability of the shower simulation program CORSIKA with respect to particle transport, decays, treatment of low-energy particles, etc A good description of the data has been found at large distances from the shower core for several interaction models The inner part of the hadron distribution, on the other hand, reveals pronounced differences among interaction models Several hadronic observables are compared with CORSIKA simulations using the QGSJET, VENUS and SIBYLL models QGSJET reproduces the hadronic distributions best At the highest energy, in the 10 PeV region, however, none of these models can describe the experimental data satisfactorily The expected number of hadrons in a shower is too large compared with the observed number, when the data are classified according to the muonic shower size

On astrophysical solution to ultrahigh energy cosmic rays

Abstract: We argue that an astrophysical solution to the ultrahigh energy cosmic ray (UHECR) problem is viable. The detailed study of UHECR energy spectra is performed. The spectral features of extragalactic protons interacting with the cosmic microwave background (CMB) are calculated in a model-independent way. Using the power-law generation spectrum $\ensuremath{\propto}{E}^{\ensuremath{-}{\ensuremath{\gamma}}_{g}}$ as the only assumption, we analyze four features of the proton spectrum: the GZK cutoff, dip, bump, and the second dip. We found the dip, induced by electron-positron production on the CMB, to be the most robust feature, existing in energy range $1\ifmmode\times\else\texttimes\fi{}{10}^{18}\char21{}4\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }\mathrm{eV}$. Its shape is stable relative to various phenomena included in calculations: discreteness of the source distribution, different modes of UHE proton propagation (from rectilinear to diffusive), local overdensity or deficit of the sources, large-scale inhomogeneities in the universe, and interaction fluctuations. The dip is well confirmed by observations of the AGASA, HiRes, Fly's Eye, and Yakutsk detectors. With two free parameters (${\ensuremath{\gamma}}_{g}$ and flux normalization constant) the dip describes about 20 energy bins with ${\ensuremath{\chi}}^{2}/\mathrm{d}.\mathrm{o}.\mathrm{f}.\ensuremath{\approx}1$ for each experiment. The best fit is reached at ${\ensuremath{\gamma}}_{g}=2.7$, with the allowed range 2.55\char21{}2.75. The dip is used for energy calibration of the detectors. For each detector independently, the energy is shifted by factor $\ensuremath{\lambda}$ to reach the minimum ${\ensuremath{\chi}}^{2}$. We found ${\ensuremath{\lambda}}_{\mathrm{Ag}}=0.9$, ${\ensuremath{\lambda}}_{\mathrm{Hi}}=1.2$, and ${\ensuremath{\lambda}}_{\mathrm{Ya}}=0.75$ for the AGASA, HiRes, and Yakutsk detectors, respectively. Remarkably, after this energy shift the fluxes and spectra of all three detectors agree perfectly, with discrepancy between AGASA and HiRes at $Eg1\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{eV}$ being not statistically significant. The excellent agreement of the dip with observations should be considered as confirmation of UHE proton interaction with the CMB. The dip has two flattenings. The high energy flattening at $E\ensuremath{\approx}1\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }\mathrm{eV}$ automatically explains ankle, the feature observed in all experiments starting from the 1980s. The low-energy flattening at $E\ensuremath{\approx}1\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }\text{ }\mathrm{eV}$ reproduces the transition to galactic cosmic rays. This transition is studied quantitatively in this work. Inclusion of primary nuclei with a fraction of more than 20% upsets the agreement of the dip with observations, which we interpret as an indication of the acceleration mechanism. We study in detail the formal problems of spectra calculations: energy losses (the new detailed calculations are presented), the analytic method of spectrum calculations, and the study of fluctuations with the help of a kinetic equation. The UHECR sources, AGN and GRBs, are studied in a model-dependent way, and acceleration is discussed. Based on the agreement of the dip with existing data, we make the robust prediction for the spectrum at $1\ifmmode\times\else\texttimes\fi{}{10}^{18}\char21{}1\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{eV}$ to be measured in the nearest future by the Auger detector. We also predict the spectral signature of nearby sources, if they are observed by Auger. This paper is long and contains many technical details. For those who are interested only in physical content we recommend the Introduction and Conclusions, which are written as autonomous parts of the paper.

The Astrophysics of Ultrahigh-Energy Cosmic Rays

Abstract: The origin of the highest energy cosmic rays is still unknown. The discovery of their sources is expected to reveal the workings of the most energetic astrophysical accelerators in the Universe. Current observations show a spectrum consistent with an origin in extragalactic astrophysical sources. Candidate sources range from the birth of compact objects to explosions related to gamma-ray bursts or to events in active galaxies. We discuss the main effects of propagation from cosmologically distant sources, including interactions with cosmic background radiation and magnetic fields. We examine possible acceleration mechanisms leading to a survey of candidate sources and their signatures. New questions arise from an observed hint of sky anisotropies and an unexpected evolution of composition indicators. Future observations may reach the necessary sensitivity to achieve charged particle astronomy and to observe ultrahigh-energy photons and neutrinos, which may further illuminate the workings of the Universe a...

Cosmic Rays and Particle Physics

Abstract: The study of high energy cosmic rays is a diversified field of observational and phenomenological physics addressing questions ranging from shock acceleration of charged particles in various astrophysical objects, via transport properties through galactic and extragalactic space, to questions of dark matter, and even to those of particle physics beyond the Standard Model including processes taking place in the earliest moments of our Universe. After decades of mostly independent evolution of nuclear-, particle- and high energy cosmic ray physics we find ourselves entering a symbiotic era of these fields of research. Some examples of interrelations will be given from the perspective of modern Particle-Astrophysics and new major experiments will briefly be sketched.