Air Shower Observatory Research Articles

Atmospheric monitoring and its impact on air shower observables at the Pierre Auger Observatory

The Pierre Auger Observatory, completed in September 2008, detects cosmic rays by observing and studying the development of extensive air showers in atmosphere. The atmosphere itself, with its unpredictable changes of conditions, directly influences the estimation of the air shower characteristics. In this paper, all the instruments and techniques adopted by the Auger Observatory are explained, and the impact of their results on the most important shower parameters are shown.

Multiple scattering of light and its impact on observations of extensive air showers

Atmospheric scattering of light emitted by an air shower not only attenuates direct fluorescence light from the shower, but also contributes to the observed shower light. So far only direct and singly-scattered Cherenkov photons have been taken into account in routine analyses of the observed optical image of air showers. A Monte Carlo method for evaluating the contribution of multiply scattered light to the optical air shower image is presented, as well as results of simulations at various atmospheric conditions. Presented are parameterizations of scattered light contributions to measured shower signals, which can be implemented into UHE shower reconstruction in the fluorescence technique.

Recent results of the LOPES experiment

LOPES measures radio pulses from extensive air showers and aims to calibrate the emitted signal in the primary energy range of 10 16 –10 18 eV. LOPES, a digital radio interferometer using high bandwidths and fast data processing, is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and profits from the reconstructed air shower observables of KASCADE-Grande. We report about recent analysis results of the radio signals measured by LOPES.

Searching for new physics with ultrahigh energy cosmic rays

Ultrahigh energy cosmic rays (UHECRs) that produce giant extensive showers of charged particles and photons when they interact in the Earth's atmosphere provide a unique tool to search for new physics. Of particular interest is the possibility of detecting a very small violation of Lorentz invariance such as may be related to the structure of space-time near the Planck scale of ∼10−35 m. We discuss here the possible signature of Lorentz invariance violation (LIV) on the spectrum of UHECRs as compared with present observations of giant air showers. We also discuss the possibilities of using more sensitive detection techniques to improve searches for LIV in the future. Using the latest data from the Pierre Auger Observatory, we derive a best fit to the LIV parameter of 3.0+1.5−3.0×10-23, corresponding to an upper limit of 4.5×10-23 at a proton Lorentz factor of ∼2×1011. This result has fundamental implications for quantum gravity models.

On the measurement of the proton-air cross section using air shower data

The analysis of high-energy air shower data allows one to study the proton-air cross section at energies beyond the reach of fixed target and collider experiments. The mean depth of the first interaction point and its fluctuations are a measure of the proton-air particle production cross section. Since the first interaction point in air cannot be measured directly, various methods have been developed in the past to estimate the depth of the first interaction from air shower observables in combination with simulations. As the simulations depend on assumptions made for hadronic particle production at energies and phase space regions not accessible in accelerator experiments, the derived cross sections are subject to significant systematic uncertainties. The focus of this work is the development of an improved analysis technique that allows a significant reduction of the model dependence of the derived cross section at very high energy. Performing a detailed Monte Carlo study of the potential and the limitations of different measurement methods, we quantify the dependence of the measured cross section on the hadronic interaction model used. Based on these results, a general improvement of the analysis methods is proposed by introducing the actually derived cross section already in the simulation of reference showers. The reduction of the model dependence is demonstrated for one of the measurement methods.

Recent Results from KASCADE-Grande and LOPES

KASCADE-Grande is an extensive air-shower experiment located at Forschungszentrum Karlsruhe, Germany. Main parts of the experiment are the Grande array spread over an area of 700 × 700 m 2 , the original KASCADE array covering 200 × 200 m 2 with unshielded and shielded detectors, and additional muon tracking devices. This multi-detector system allows to investigate the energy spectrum, composition, and anisotropies of cosmic rays in the energy range up to 1 EeV. LOPES is co-located at the same site to measure radio pulses from extensive air showers in coincidence with KASCADE-Grande. It consists of 30 digital antennas operated in different geometrical configurations. Read out is performed at high bandwidths and rate data processing with the aim to calibrate the emitted signal in the primary energy range of 10 16 − 10 18 eV by making use of reconstructed air-shower observables of KASCADE-Grande. An overview on the performance of both experiments will be given and recent analysis results be reported.

Air shower measurements with the LOPES radio 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. Since radio waves suffer very little attenuation, radio measurements allow the detection of very distant or highly inclined showers. These waves can be recorded day and night, and provide a bolometric measure of the leptonic shower component. LOPES is designed as a digital radio interferometer using high bandwidths and fast data processing and profits from the reconstructed air shower observables of KASCADE-Grande. The LOPES antennas are absolutely amplitude calibrated allowing to reconstruct the electric field strength which can be compared with predictions from detailed Monte-Carlo simulations. We report about the analysis of correlations present in the radio signals measured by the LOPES 30 antenna array. Additionally, LOPES operates antennas of a different type (LOPES STAR ) which are optimized for an application at the Pierre Auger Observatory. Status, recent results of the data analysis and further perspectives of LOPES and the possible large scale application of this new detection technique are discussed.

Detection of TeV to PeV Neutrinos and Gamma-Rays with the High Mountain SHALON Mirror Cherenkov Telescope

Problems in observation of extensive air showers generated by neutrinos are connected with an extremely small cross section of inelastic collisions of neutrinos with nuclei. However, two facts allow to search for showers generated by neutrinos: (1) a hadron cascade with the primary energy of more than 10 13 eV leaves a mountain ridge to the atmosphere from the depth 300 g/cm 2 without an essential loss of the total energy in the hadron cascade, and (2) air Cherenkov radiation from such hadron cascades will be observed with a 7.5 km distant telescope over an area of more than 7 ×10 5 m 2 . This partially compensates the small cross section of inelastic neutrino collisions. The observation has been carried out since 1992 at high mountainous Tien-Shan station with SHALON Cherenkov mirror telescope with ∼11.2 m 2 mirror area and image matrix of 144 PMT with full angle >8°. The telescope characteristics permitted to start the search of local neutrino sources with energy 10 13 –10 16 eV on EAS generating in mou...

Air fluorescence relevant for cosmic-ray detection—Summary of the 5th fluorescence workshop, El Escorial 2007

High-energy cosmic rays with energies exceeding 10 17 eV are frequently observed by measurements of the fluorescence light induced by air showers. A major contribution to the systematic uncertainties of the absolute energy scale of such experiments is the insufficient knowledge of the fluorescence light yield of electrons in air. The aim of the 5th Fluorescence Workshop was to bring together experimental and theoretical expertise to discuss the latest progress on the investigations of the fluorescence light yield. The results of the workshop will be reviewed as well as the present status of knowledge in this field. Emphasis is given to the fluorescence light yield important for air shower observations and its dependence on atmospheric parameters, like pressure, temperature, and humidity. The effects of the latest results on the light observed from air showers will be discussed.

The origin of galactic cosmic rays

The origin of galactic cosmic rays is one of the most interesting unsolved problems in astroparticle physics. Experimentally, the problem is attacked by a multi-disciplinary effort, namely by direct measurements of cosmic rays above the atmosphere, by air shower observations, and by the detection of TeV γ rays. Recent experimental results are presented and their implications on the contemporary understanding of the origin of galactic cosmic rays are discussed.

Primary energy spectrum of cosmic rays obtained by arrival time spread of particles in EAS

The Large Area Air Shower (LAAS) group has been performing a network observation of extensive air showers (EAS) by using compact arrays. According to J. Linsley, the primary energy of EAS can be estimated from the spread of the arrival times of EAS particles, even with a small array. A shift register system for clocking the arrival times was installed in an array (OUS1) which is located in Okayama University of Science. Analyzing the OUS1 data, we obtained the primary energies of large air showers.

TeV to PeV neutrinos and gamma-rays with Mountain SHALON Mirror Cherenkov Telescope

Problems in observation of extensive air showers generated by neutrinos are connected with an extremely small cross-section of inelastic collisions of neutrinos with nuclei. However, two facts allow to search for showers generated by neutrinos: (1) a hadron cascade with a primary energy of more than 10 13 eV leaves a mountain ridge to the atmosphere from a depth ∼ 300 g / cm 2 without any essential loss of the total energy in the hadron cascade, and (2) air Cherenkov radiation from such hadron cascades will be observed with a 7.5 km distant telescope over an area of more than 7 × 10 5 m 2 . This partially compensates for the small cross-section of inelastic neutrino collisions. Observations have been carried out since 1992 at the high mountain Tien-Shan station using the SHALON Cherenkov mirror telescope with ∼11.2 m 2 mirror area and image matrix of 144 PMT with full angle >8°. The telescope characteristics allowed to start searching for local neutrino sources with energy 10 13 –10 16 eV on EAS generated in the mountain-range located at some 7.5 and more kilometers from the gamma-telescope (in Russian the abbreviation SHALON means - the Extensive Air Showers from Neutrino).

Study on nuclear composition of cosmic rays around the knee utilizing muon multiplicity with GRAPES-3 experiment at Ooty

The composition and energy spectrum of primary cosmic rays (PCRs) are the only observables available at ultra-high energies to understand the nature of sources accelerating protons and other nuclei to 1000 TeV and beyond. These observables have been measured up to 1000 TeV, directly with detectors flown aboard balloons and satellites. The measurements at > 1000 TeV are obtained indirectly, from ground based observations of extensive air showers (EAS). However, their interpretation depends on rather inadequate knowledge of hadronic interactions at > 1000 TeV . The GRAPES-3 experiment has been designed to study the EAS at ∼ 30 TeV to provide a sizable overlap with the results from direct measurements, enabling selection of a suitable model of hadronic interactions. We present here the salient features of GRAPES-3 experiment and some details of muon multiplicity distributions (MMDs) observed with a 560 m2 muon detector as a function of shower size ( N e ) fro analysis of 560 days of data. A comparison of GRAPES-3 results with direct measurements over the energy region 100 – 1000 TeV is presented to show the suitability of hadronic interaction generator “SIBYLL” for the interpretation of EAS data. We presented the energy spectrum of five nuclear groups (H, He, N, Al and Fe) with good statistics for 100 – 10, 000 TeV.

The cosmic-ray knee and ensuing spectrum seen as a consequence of Bell's self-magnetized SNR shock acceleration process

Bell's version of diffusive shock acceleration in supernova remnants, in which the (highly contorted) magnetic field is mainly self-generated by the accelerated particles, seems to explain the sharpness of the knee in the cosmic ray spectrum (an effect of the limitation of acceleration in the source), despite contributions from very many supernovae; and the expected knee has a sharp drop near 3 PV rigidity for each nuclear species, and then a lower rounded shoulder extending towards 100 PV contributed by some of the type II SNRs. It is shown that the allparticle flux determined by very different techniques in air shower observations defines a very precise spectrum, below 1019 eV, and this spectrum is discussed in terms of separate nuclear components of Galactic and extragalactic origin. An extragalactic component with similar source spectrum to the Galactic component is favoured, but a helium/hydrogen mixture and a pure proton flux from the extragalactic sources have different attractions, and offer different tests through composition, even below 1018 eV.

Impact of varying atmospheric profiles on extensive air shower observation: Fluorescence light emission and energy reconstruction

Several experiments measure the fluorescence light produced by extensive air showers in the atmosphere. This light is converted into a longitudinal shower profile from which information on the primary energy and composition is derived. The fluorescence yield, as the conversion factor between light profile measured by EAS experiments and physical interpretation of showers, has been measured in several laboratory experiments. The results, however, differ considerably. In this article, a model calculation of the fluorescence emission from relevant band systems of nitrogen in dependence on wavelength and atmospheric conditions is presented. Different calculations are compared to each other in combination with varying input parameters. The predictions are compared with measurements and the altitude dependence of the fluorescence yield is discussed in detail.

Detection of metagalactic and galactic sources of very high-energy gamma-quanta and neutrinos with the mirror Cherenkov telescope SHALON

Gamma-astronomy and neutrino astronomy are unique experimental possibilities to search for sources of high-energy cosmic rays ( 10 12 – 10 14 eV ) . Experimental data on sources of γ -quanta with the energy > 1 TeV are characterized by the fact that observed metagalactic sources (active galactic nuclei), being different in power from galactic sources by the factor of 10 6 – 10 7 , do not differ in the energy spectrum, F ( > E γ ) ∝ E γ - 1.3 ± 0.15 . The power of the metagalactic sources and their unlimited number casts doubts on the assumption of a galactic origin of the observed cosmic-ray flux. It is possible to assume that the uniform cosmic-ray spectrum is formed by “braking” in multiple elastic or inelastic collisions with relict photons in intergalactic space. Thus, the observed distribution of protons and cosmic-ray nuclei with the spectral index 2.72 ± 0.02 ( = 2.718 … , the Napier's constant) may be a consequence of such a “braking” that warms up the relict photons. Problems in observation of extensive air showers generated by neutrinos are connected with an extremely small cross section of inelastic collisions of neutrinos with nuclei. However, two facts allow to search for showers generated by neutrinos: (1) a hadron cascade with the primary energy of more than 10 12 eV leaves a mountain ridge to the atmosphere from the depth ∼ 300 g / cm 2 without an essential loss of the total energy in the hadron cascade, and (2) air Cherenkov radiation from such hadron cascades will be observed with a 7.5 km distant telescope over an area of more than 7 × 10 5 m 2 . This partially compensates the small cross section of inelastic neutrino collisions.

Photon air showers at ultra-high energy and the photonuclear cross-section

Experimental conclusions from air shower observations on cosmic-ray photons above 10^19 eV are based on the comparison to detailed shower simulations. For the calculations, the photonuclear cross-section needs to be extrapolated over several orders of magnitude in energy. The uncertainty from the cross-section extrapolation translates into an uncertainty of the predicted shower features for primary photons and, thus, into uncertainties for a possible data interpretation. After briefly reviewing the current status of ultra-high energy photon studies, the impact of the uncertainty of the photonuclear cross-section for shower calculations is investigated. Estimates for the uncertainties in the main shower observables are provided. Photon discrimination is shown to be possible even for rapidly rising cross-sections. When photon-initiated showers are identified, it is argued that the sensitivity of photon shower observables to the photonuclear cross-section can in turn be exploited to constrain the cross-section at energies not accessible at colliders.

On the influence of cross sections and elasticities of hadronic interactions on air shower observables

To investigate the impact of uncertainties in the knowledge of properties of individual hadronic interactions on the development of extensive air showers, the inelastic proton-proton cross section and the elasticity of interactions have been modified within the interaction model QGSJET. Air shower simulations are performed using the CORSIKA code. The influence of the modifications on observables like the number of electrons, muons, and hadrons registered at ground level are investigated. The predictions are compared to measurements of the KASCADE experiment.

Search for very high-energy neutrinos by SHALON (Cherenkov radiation of extensive air showers observed at large zenith angles)

The detection of extraterrestrial very high energy neutrinos by the atmospheric Cherenkov telescopic system SHALON is discussed. The analysis of results of observation of extensive air showers at 3338 m above sea level by means of the gamma-telescope SHALON at zenith angles 72°, 76°, 84°, 96° are presented. The observed results are compared with the data of of shower according to zenith angle. The observation has been carried out at Tien-Shan station with SHALON gamma-telescope. The SHALON telescopic system has mirror with area of 11.2 m 2 and 144 PMT matrix with 0.2° angular resolution, and has the largest angular acceptance in the world - > 8°. It allows to continuously control the background of cosmic ray particle emission and the atmospheric transparency with observation thus increasing observation efficiency. It is the telescope characteristics that permit to start searching for local neutrino sources with energy 10 13 − 10 15 eV on EAS generated in mountain-range located at some 5 and more kilometers from the gamma-telescope (in Russian the SHALON abbreviation means - the Extensive Air Showers from Neutrino).

The Pierre Auger Observatory – status and prospects

The southern Pierre Auger Observatory is presently under construction in Malargue, Mendoza, Argentina. It combines two complementary air shower observation techniques; the detection of particles at ground and the observation of associated fluorescence light generated in the atmosphere above the ground. Experimentally, this is being realised by employing an array of 1600 water Cherenkov detectors, distributed over an area of 3000 km^2, and operating 24 wide-angle Schmidt telescopes, positioned at four sites at the border of the ground array. The Observatory will reach its full size in 2006. However, with the 540 tanks and 12 telescopes presently in operation, the Pierre Auger Observatory has become the largest world-wide cosmic ray experiment already now. This paper sketches the experimental set-up and discusses the current status. In parallel to the ongoing completion of the experiment, a large number of events have been detected with energies above 10^19 eV. The data are used to verify both the performance of the individual detector components as well as to test the quality of the hybrid event reconstruction. All results obtained so far are very promising and they underline the great advantages of the chosen hybrid approach.