Properties Of Showers Research Articles

Inconsistencies in EAS simulations — longitudinal vs. lateral development

In present-day air shower experiments several techniques are used to determine shower properties, e.g. the electromagnetic, muonic, and hadronic components as well as the Cerenkov and fluorescence light are investigated. The all particle spectrum of cosmic rays and the mean logarithmic mass have been derived. Most all-particle energy spectra are compatible with extrapolations of the energy spectra of individual elements, measured directly at the top of the atmosphere. An investigation of the mean logarithmic mass derived from EAS observables yields systematic differences between experiments measuring the lateral EAS development on one side and experiments investigating the longitudinal EAS development on the other hand. The inconsistencies can be reconciled by reducing the logarithmic increase of the total inelastic hadronic cross sections as function of energy.

Synchrotron radiation at radio frequencies from cosmic ray air showers

We review some of the properties of extensive cosmic ray air showers and describe a simple model of the radio-frequency radiation generated by shower electrons and positrons as they bend in the Earth’s magnetic field. We perform simulations by calculating the trajectory and radiation of a few thousand charged shower particles. The results are then transformed to predict the strength and polarization of the electromagnetic radiation emitted by the whole shower.

A Method for Determining the Coordinates of Meteor Shower Radiants from Meteor Radar Goniometric Data

We discuss a new method for measuring the coordinates of meteor shower radiants from meteor radar data. The method uses a high accuracy of radar goniometer measurements of one of the angular coordinates for meteor radiants and collective properties of incident meteor showers. It is based on a computer technology of searching for the coordinates of radiants using the intersections of meteor position lines on the celestial sphere and filtering nonrandom combinations of these intersections. The method allows the following: to detect meteor showers with a rate of more than 5 per day of observations and to separate meteor groups from different meteor showers with different radiants and velocities. The method makes it possible to increase the angular resolution from 10° × 10° achieved with a quasi-tomographic technique to 2° × 2°, with a prospect of a further increase in the accuracy through the individual reduction of separated meteor groups. We use the reduction of one-day-long observations during maximum activity of the Geminids meteor shower in 1993 to illustrate the potentialities of the method. We show an example of detecting a weak meteor shower that was active during December 1993.

Upper Limit on Gamma-Ray Flux above 10[TSUP]19[/TSUP] [CLC]e[/CLC]V Estimated by the Akeno Giant Air Shower Array Experiment

The origin of the highest energy cosmic rays (≥1020 eV) is not well understood. Interesting models called top-down scenarios have been proposed to explain the origin. The γ-ray flux in ultra-high-energy cosmic rays is a key parameter for giving constraints on such models. To study the properties of γ-ray showers, we carry out simulation studies that take into account both the Landau-Pomeranchuk-Migdal effect and electromagnetic interactions in the geomagnetic field. Based on an analysis of muons in air showers observed by the Akeno Giant Air Shower Array, the upper limits on the γ-ray flux are estimated to be 28% above 1019 eV and 67% above 1019.5 eV in the observed air showers at a confidence level of 95%. Above 1020 eV, the primary composition is in agreement with an extrapolation from lower energies, and there is no indication that the observed events are mostly γ-ray showers. These results provide observational constraints for origin models up to the highest energies.

Characteristics of air showers produced by extremely high energy gamma-rays

The technique of adjoint cascade equations has been applied to calculate the properties of air showers produced by extremely high energy (EHE) γ-rays in the energy range 1018–1022 eV. The high intrinsic accuracy, combined with very modest (compared with the traditional Monte Carlo codes) computational time requirements, make this method as an effective tool for the detailed study of development of EHE showers in the Earth's atmosphere. In this paper a wide range of parameters of γ-ray-induced showers are analysed taking into account two independent effects which become crucial for the cascade development in the EHE regime—the Landau–Pomeranchuk–Migdal (LPM) effect and the interaction of primary γ-rays with the geomagnetic field (GMF). Although the LPM effect leads to dramatic modifications of shower characteristics, especially at primary energies exceeding 1019 eV, the GMF effect, which starts to ‘work’ at approximately the same energies, prevents, to a large extent, the LPM effect by converting the primary γ-ray into a bunch of synchrotron γ-ray photons with energies effectively below the threshold of the LPM effect. This bunch of secondary photons hits the atmosphere and creates a large number of simultaneous showers. The superposition of these independent showers mimics a single shower with energy E = ∑Ei ≃ E0, but without the signatures of the LPM effect. This makes the longitudinal profile of such a composite electromagnetic shower quite similar to the longitudinal profile of hadronic showers. At the same time, the number of muons as well as their lateral distribution differ significantly from the corresponding parameters of proton-induced showers. In the ‘gamma-ray bunch’ regime, the total number of muons is less, by a factor of 5–10, than the number of muons in hadronic showers. Also, compared with the hadronic showers, the electromagnetic showers are characterized by a significantly narrower lateral distribution of muons. Even so, for inclined EHE γ-ray showers the density of muon flux at large distances from the shower core (≥1000 m) can exceed the electron density.

MULTIFRACTAL ANALYSIS OF 1/f FLUCTUATIONS IN SIMULATED EXTENSIVE AIR SHOWERS PRODUCED BY DIFFERENT PRIMARY COSMIC RAY

As was pointed out in some recent papers, the fluctuations in the secondary particle distribution of extensive air showers at observation level exhibit a complex structure which can be interpreted as a white noise plus a 1/f noise. The resulting coloured noise fits very well into the framework of the universal multitractal theory. In this paper we compare the e+ and e- density fluctuations generated by different primary cosmic rays, namely, high energy γ rays, protons, and helium, oxygen and iron nuclei, and the universal multifractal parameters for all these primaries are calculated for several samples. The performed analysis reveals that the Levy index and the mean codimension depend monotonically on the mass of the primary cosmic ray. Some future applications of the multifractal properties of extensive air showers are suggested.

The fluorescence detector prototype for the Auger project: mechanical structure, optical system, and filter

The Pierre Auger Observatory will study cosmic rays with energy exceeding 10/sup 19/ eV. The experiment will measure properties of extensive air showers with a hybrid detector consisting of a surface array and an atmospheric fluorescence telescope. This paper presents the characteristics and performance of the optical system for the fluorescence detector prototype. The system adopts a Schmidt camera design with a diaphragm to remove coma aberration. A large spherical mirror (approximately 3.6/spl times/3.6 m, with radius of curvature 3.47 m), segmented in 49 trapezoidal elements, is supported by a mechanical structure, where segments are positioned on the meridians of the spherical cap. At the diaphragm, an absorption filter is installed to preferentially transmit the nitrogen fluorescence light. The construction technique, image characteristics, and results of tests performed on the system are discussed.

Cosmic rays of energies in the range 103–105 TeV and higher

Over a period of more than 30 years, the knee in the spectrum of extensive air showers (EAS) generated by cosmic radiation has been explained in two ways: as a consequence of a cusp in the energy spectrum of primary cosmic rays or as a consequence of a change undergone by the process of multiparticle hadron production in the interactions of primary protons with nuclei of air atoms. Investigations at the Tien Shan EAS array confirm a change in the properties of showers generated by protons near the upper boundary of the atmosphere and evince the invariability of the energy spectrum of protons in the energy range 103–105 TeV.

Exotic massive hadrons and ultrahigh energy cosmic rays

We investigate the proposal that primary cosmic rays of energy above the Greisen-Zatsepin-Kuzmin cutoff are exotic massive strongly interacting particles (uhecrons). We study the properties of air showers produced by uhecrons and find that masses in excess of about 50 GeV are inconsistent with the highest energy event observed. We also estimate that with sufficient statistics a uhecron of mass as low as 10 GeV may be distinguished from a proton.

A new method to reconstruct the energy and determine the composition of cosmic rays from the measurement of Cherenkov light and particle densities in extensive air showers

A Monte Carlo study to reconstruct energy and mass of cosmic rays with energies above 300 TeV using ground based measurements of the electromagnetic part of showers initiated in the atmosphere is presented. The shower properties determined with two detector arrays measuring the air Cherenkov light and the particle densities as realized at the HEGRA experiment are processed to determine the energy of the primary particle without the need of any hypothesis concerning its mass. The mass of the primary particle is reconstructed coarsely from the same observables in parallel to the energy determination.

The dual imaging cerenkov experiment (DICE) and the elemental composition in the “Knee” region

An outstanding problem in cosmic ray physics is the cosmic ray elemental abundance in the “knee” region of the charged particle spectrum. The Dual Imaging Cerenkov Experiment (DICE) is designed to measure the mean elemental mass and energy spectrum around the “knee” energy by using composition sensitive properties of Extensive Air Showers (EAS). We present preliminary results on one EAS parameter, the average depth of shower maximum, 〈 X max 〉. We also show evidence for a change in the cosmic ray spectral index, a result which is in qualitative agreement with other experiments. A small increase in 〈 X max 〉 is present at the onset of the “knee”, implying an increase in the relative number of lighter elements. Further consistency tests of these results which are in progress are described.

Improvement of gamma-hadron discrimination at TeV energies using a new parameter, image Surface Brightness

The recent advances in TeV γ-ray astronomy using imaging Cerenkov telescopes is mainly due to the good separation between the properties of γ-ray and hadronic showers. A new method for this discrimination is described. The method is mainly based on the change of the image's Size and Surface Brightness (Size/Area) with energy and the differences in these parameters between those initiated by γ-rays and hadrons. The application of the method to the Whipple's 10 m telescope database from the Crab Nebula and Markarian 421 demonstrates its sensitivity to gamma-hadron separation. This study shows the importance of the image Surface Brightness, in addition to the previously used Shape and Orientation parameters.

Shower simulation: lessons from MOCCA

The paper describes one approach to the Monte-Carlo simulation of extensive air showers of energy in the range 1012 to 1021 eV, using thin sampling for particles of energy much below the energy of the primary particle. Experience of this approach using the MOCCA program is outlined. Also, it is argued that only a few features of hadronic interactions are important in determining shower properties, and that the far plateau region of particle production is of little importance, and hence a simplified hadron interaction algorithm, as employed in MOCCA, is useful. Methods of demonstrating the contribution of different features of the interactions to observable aspects of showers are illustrated. The importance of secondary spectra from pion-air collisions in influencing the depth of maximum is highlighted.

Elemental composition of cosmic rays using a maximum likelihood method

We present a progress report on our attempts to determine the composition of cosmic rays in the “knee” region of the energy spectrum. We have used three different devices to measure properties of the extensive air showers produced by primary cosmic rays: the Soudan 2 underground detector measures the muon flux deep underground, a proportional tube array samples shower density at the surface of the earth, and a Cherenkov array observes light produced high in the atmosphere. We have begun maximum likelihood fits to these measurements with the hope of determining the nuclear mass number A on an event by event basis.

Monte Carlo simulation of photon-induced air showers

The EPAS code (Electron Photon-induced Air Showers) is a three-dimensional Monte Carlo simulation developed to study the properties of extensive air showers (EAS) generated by the interaction of high energy photons (or electrons) in the atmosphere. Results of the present simulation concern the longitudinal, lateral, temporal and angular distributions of electrons in atmospheric cascades initiated by photons of energies up to 10 3 TeV.

Shower properties relevant to large arrays

If a giant detector array is used to observe showers above 1 EeV, measurements of the air scintillation light and its ratio to Cerenkov light might usefully indicate the depth of shower development. The proportion of muons remains a useful indicator of primary mass: their height of origin appears to be a less sensitive indicator of mass.

Electromagnetic pulses from high-energy showers: Implications for neutrino detection.

We review the properties of electromagnetic showers in dense media and calculate in detail the associated electromagnetic pulses generated by shower electrons. We perform real-time simulations recording the charge, trajectory, and time of each cascade particle and compute the associated electromagnetic wave. Our results are relevant to experiments detecting radio pulses from showers initiated by cosmic particles interacting with the Earth.

Electromagnetic cascade showers in lead with the Landau-Pomeranchuk-Migdal effect included: Average behavior of the one-dimensional LPM shower in lead.

The numerical method developed by Fujimaki and Misaki can obtain solutions for an electromagnetic cascade shower, in which no restrictions on the forms of the differential cross sections for both bremsstrahlung and pair-production processes are made. By utilizing this method, the LPM showers (electromagnetic cascade showers in the presence of the Landau Pomeranchuk-Migdal effect) are calculated for primary energies in the range ${10}^{14}$-${10}^{17}$ eV in lead. Physical properties of the LPM showers, such as electron transition curves, track lengths, and fractional dissipated energies, are obtained in the cases with and without the inclusion of ionization losses. In order to compare LPM showers with ordinary electromagnetic cascade showers in the absence of the LPM effect [hereafter defined as Bethe-Heitler (BH) showers] and to clarify the characteristics of the LPM showers, all physical quantities which have been obtained in the LPM showers have also been obtained in the BH showers. We discuss the characteristics of the LPM showers, especially with reference to the BH showers. The results obtained by other authors are compared with the results obtained by the author.

Development of cascade showers in dense media.

I have discovered a new way of solving for the evolution of an electromagnetic cascade shower when the cross sections have been altered by the density. This method relies on a set of Green's-function solutions to the usual diffusion equations of approximation A of Rossi and Greisen. The Green's functions explicitly account for the energy and density dependence of the cross sections. This technique gives distribution functions for showers in material at any density, and for all incident and final energies. In particular, this method has been used to study the development of cascade showers at the surface of a neutron-star polar cap. Particles emitted by nuclei excited by a cascade shower are thought to be an important plasma source for radio pulsars. Showers computed using the density-suppressed cross sections penetrate much deeper than the usual Bethe-Heitler showers, which reduces the importance of the excited nuclei for pulsar models. The integrated cross sections introduced by the Mellin-transform techniques of approximation A lend themselves to a description of shower evolution in terms of the mean shower properties. The solutions to the mean shower development equations are at best a rough guide to the evolution of the shower as a whole, but they clearly illustrate the increasing penetration depth of the shower caused by the reduced cross sections.

Statistical properties of cosmic-ray showers at ground level determined from photomultiplier-tube background registrations.

The fluctuations of cosmic-ray particles resulting from extensive air showers at ground level are well described by the two-parameter Poisson-driven Yule-Furry and negative-binomial counting probability distributions. The background signal from a single photomultiplier tube has been used to experimentally verify these results with remarkable precision, in spite of the simplicity of the underlying pure-birth stochastic process. Counting distributions from three different photomultiplier-tube detectors operated in the dark are presented, together with the theoretical predictions. Probability distributions of interevent times have also been obtained and these are found to be consistent with the observed clustering properties at the detector output. Our approach is expected to be of importance in quantum optics where cosmic-ray-shower particles can pose a significant limitation on the detection of squeezed light.