S. J. Sciutto

Extensive air shower simulations at the highest energies

Abstract Air shower simulation programs are essential tools for the analysis of data from cosmic ray experiments and for planning the layout of new detectors. They are used to estimate the energy and mass of the primary particle. Unfortunately the model uncertainties translate directly into systematic errors in the energy and mass determination. Aiming at energies>10 19 eV, the models have to be extrapolated far beyond the energies available at accelerators. On the other hand, hybrid measurement of ground particle densities and calorimetric shower energy, as will be provided by the Pierre Auger Observatory, will strongly constrain shower models. While the main uncertainty of contemporary models comes from our poor knowledge of the (soft) hadronic interactions at high energies, also electromagnetic interactions, low-energy hadronic interactions and the particle transport influence details of the shower development. We review here the physics processes and some of the computational techniques of air shower models presently used for highest energies, and discuss the properties and limitations of the models.

Influence of the LPM effect and dielectric suppression on particle air showers

An analysis of the influence of the Landau-Migdal-Pomeranchuk (LPM) effect on the development of air showers initiated by astroparticles is presented. The theory of Migdal is studied and compared with other theoretical methods, particularly the Blankenbecler-Drell approach. By means of realistic computer simulations and using algorithms that emulate Migdals theory, including also the so-called dielectric suppression, we study the behavior of the relevant observables in the case of ultrahigh energy primaries. We find that the LPM effect can significantly modify the development of high energy electromagnetic showers in certain cases.

Hadronic interactions models beyond collider energies

Studies of the influence of different hadronic models on extensive air showers at ultra-high energies are presented. The hadronic models considered are those implemented in the well-known QGSJET and SIBYLL event generators. The different approaches used in both codes to model the underlying physics is analyzed using computer simulations performed with the program AIRES. The most relevant observables for both single collisions and air showers are studied for primary energies ranging from

TIERRAS: A package to simulate high energy cosmic ray showers underground, underwater and under-ice

10^{14}

Extended air showers and muon interactions

eV up to

Testing hadronic interaction packages at cosmic ray energies

10^{20.5}

Hunting long-lived gluinos at the Pierre Auger Observatory

eV. In addition, the evolution of lateral and energy distributions during the shower development is presented. Our analysis seems to indicate that the behaviour of shower observables does not largely reflect the strong differences observed in single collisions.

The Influence of the geomagnetic field and of the uncertainties in the primary spectrum on the development of the muon flux in the atmosphere

Abstract In this paper we present TIERRAS, a Monte Carlo simulation program based on the well-known AIRES air shower simulations system that enables the propagation of particle cascades underground, providing a tool to study particles arriving underground from a primary cosmic ray on the atmosphere or to initiate cascades directly underground and propagate them, exiting into the atmosphere if necessary. We show several cross-checks of its results against CORSIKA, FLUKA, GEANT and ZHS simulations and we make some considerations regarding its possible use and limitations. The first results of full underground shower simulations are presented, as an example of the package capabilities. Program summary Program title: TIERRAS for AIRES Catalogue identifier: AEFO_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEFO_v1_0.html Program obtainable from: CPC Program Library, Queens University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 36 489 No. of bytes in distributed program, including test data, etc.: 3 261 669 Distribution format: tar.gz Programming language: Fortran 77 and C Computer: PC, Alpha, IBM, HP, Silicon Graphics and Sun workstations Operating system: Linux, DEC Unix, AIX, SunOS, Unix System V RAM: 22 Mb bytes Classification: 1.1 External routines: TIERRAS requires AIRES 2.8.4 to be installed on the system. AIRES 2.8.4 can be downloaded from http://www.fisica.unlp.edu.ar/auger/aires/eg_AiresDownload.html . Nature of problem: Simulation of high and ultra high energy underground particle showers. Solution method: Modification of the AIRES 2.8.4 code to accommodate underground conditions. Restrictions: In AIRES some processes that are not statistically significant on the atmosphere are not simulated. In particular, it does not include muon photonuclear processes. This imposes a limitation on the application of this package to a depth of 1 km of standard rock (or 2.5 km of water equivalent). Neutrinos are not tracked on the simulation, but their energy is taken into account in decays. Running time: A TIERRAS for AIRES run of a 10 20 eV shower with statistical sampling (thinning) below 10 12 eV and 0.2 weight factor (see [1]) uses approximately 1 h of CPU time on an Intel Core 2 Quad Q6600 at 2.4 GHz. It uses only one core, so 4 simultaneous simulations can be run on this computer. Aires includes a spooling system to run several simultaneous jobs of any type. References: [1] S. Sciutto, AIRES 2.6 User Manual, http://www.fisica.unlp.edu.ar/auger/aires/ .

Flux of atmospheric muons: Comparison between AIRES simulations and CAPRICE98 data

The objective of this work is to report on the influence of muon interactions on the development of air showers initiated by astroparticles. We make a comparative study of the different theoretical approaches to muon bremsstrahlung and muonic pair production interactions. A detailed algorithm that includes all the relevant characteristics of such processes has been implemented in the AIRES air shower simulation system. We have simulated ultrahigh energy showers in different conditions in order to measure the influence of these muonic electromagnetic interactions. We have found that during the late stages of the shower development (well beyond the shower maximum) many global observables are significantly modified in relative terms when the mentioned interactions are taken into account. This is most evident in the case of the electromagnetic component of very inclined showers. On the other hand, our simulations indicate that the studied processes do not induce significant changes either in the position of the shower maximum or the structure of the shower front surface.

ANALYSIS OF SUNSPOT NUMBER FLUCTUATIONS

A comparative analysis of the secondary particles output of the main hadronic interaction packages used in simulations of extensive air showers is presented. Special attention is given to the study of events with very energetic leading secondary particles, including diffractive interactions.