Model of cosmic ray generation

It is shown that the two bends observed in the cosmic ray energy spectrum can be well approximated by equations derived by assuming that cosmic rays can be generated and accelerated in plasma pinches. Zh. éksp. Teor. Fiz. 111, 385–403 (February 1997)     

Change of primary cosmic ray mass composition at superhigh energies

The EAS MSU array experimental data are analyzed in relation to the primary cosmic ray composition in the energy range above 10¹⁷–10¹⁸ eV. The problem of the existence of an additional cosmic ray component, which cannot be explained in the framework of traditional mechanism of Galactic cosmic ray production, is considered. The fraction of gamma-quanta in the primary cosmic radiation is evaluated as well.     

Bremsstrahlung photons from cosmic ray muons of high and ultrahigh energies

The results from calculations for fluxes of bremsstrahlung photons generated at different depths in the atmosphere by cosmic ray muons with energies of up to 10¹⁰ GeV are presented. It is shown that the generation of charmed particles in the atmosphere, along with the generation of J/ψ mesons, must be taken into account in interpretations of experimental data on studying EASes at high and ultrahigh energies.     

Confronting models of cosmic ray interactions with particle physics at LHC energies

Inelastic pp collisions are dominated by soft (low momentum transfer) physics, to which perturbative QCD cannot be fully applied. A deep understanding of both soft and semi-hard processes is crucial for predictions of minimum bias and underlying events of the pp large hadron collider (LHC) now coming on line. Moreover, the interaction of cosmic ray particles entering in the atmosphere is extremely sensitive to these soft processes and consequently cannot be formulated from first principles. Because of this, air shower analyses strongly rely on hadronic interaction models, which extrapolate collider data by several orders of magnitude. A comparative study of Monte Carlo simulations of pp collisions (at the LHC center-of-mass energy ≃14 TeV) using the most popular hadronic interaction models for ultrahigh energy cosmic ray (SIBYLL and QGSJET) and for collider physics (the PYTHIA multiparton model) is presented. The most relevant distributions are studied including the observables from diffractive events with the aim of discriminating between the different models. PACS 13.85.-t; 96.40.-z     

Modified Duller-Walker approach to study N-N collision events at cosmic ray energies

High energy nucleon-nucleon collision events are analysed in the light of modified Duller-Walker approach as proposed in a recent paper by Ghosh et al. The result of the analysis clearly justifies the validity of the modified D. W. approach in the cosmic ray energy from 100 to 10,000 GeV.     

Inelastic interactions of cosmic ray particles with atomic nuclei at very high energies

The nucleon-nucleus inteactions in the energy range T=100–1000 GeV are analysed from the point of view of the mechanism of intranuclear cascades in its generally accepted form (as a series of independent two-particle interactions). According to the presently available experimental data, it was taken into account that among secondary particles produced in high-energy inelastic nucleon-nucleon and pion-nucleon collisions there is a leading particle carrying away about 70% of the total energy. Consideration of this fact leads to the result that the cascade calculation is strongly contradictory with the experimental data. To obtain agreement between theory and experiment it is necessary, in the calculation of the intranuclear cascades, to take into consideration many-particle interactions of last particles inside the nucleus. A change in the usual form of the cascade mechanism of nucleon-nucleus interactions occurs at an energy of several dozens of GeV.     

Induction mechanism of cosmic ray production and kinks in the cosmic ray spectrum

Two kinks are observed in the energy spectrum of galactic cosmic rays. It is shown that the entire spectrum can be described, to a good approximation, by a single formula obtained on the basis of the hypothesis that the particles are produced and accelerated in plasma pinches by an induction mechanism under the assumption that three hierarchical groups of currents are present—interstellar, galactic, and metagalactic. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 225–230 (25 August 1996)     

Cosmic rays at the highest energies

Cosmic rays at the highest energies are observed with the Pierre Auger Observatory. Recent results are discussed and the properties of high-energy cosmic rays are reviewed.     

Identification of the primary cosmic ray

The nature of the primary particle giving rise to an atmospheric shower may be, to some extent, inferred from the observable properties: longitudinal profile (especially position of the maximum of the number of charged particles) or shape at ground level (lateral distribution, curvature and thickness of the shower front, muonic component). Distinguishing different nuclei cannot be performed unambiguously on a single shower, because of the random fluctuations in the first steps of the cascade; however, it is possible to study the composition of the incident flux on a statistical basis: showers from heavier nuclei have a faster development, and contain more muons. The uncertainties on the hadronic interactions at the highest energies limit the reliability of the identification. Other primaries, if they exist, could be easier to distinguish. Photons would give a slower development than protons, especially at highest energies, and a very reduced muonic component; neutrinos would be characterized by deep interactions in the atmosphere, or even within the Earth, giving almost horizontal showers with a large electromagnetic component, clearly different from the muonic tail of showers induced in the upper atmosphere by nuclei. Such ‘exotic’ primaries have not yet been observed. To cite this article: P. Billoir, P. Sommers, C. R. Physique 5 (2004).     

Primary cosmic ray flux

We discuss the primary cosmic ray flux from the point of view of particle interactions and production of atmospheric neutrinos. The overall normalization of the cosmic ray flux and its time variations and site dependence are major ingredients of the atmospheric neutrino predictions and the basis for the derivation of the neutrino oscillation parameters.     

Energy spectrum of cosmic rays and multiparticle generation of hadrons at ultrahigh energies

None of the presently known local sources of photons whose energy exceeds 10¹² eV is incompatible with the universal energy spectrum F(>E _γ ) ～ E _γ ^?1.36±0.15 . The power of extragalactic sources is 10⁶ to 10¹² times higher than the power of galactic sources since the respective distances are longer in the former case, while the observed flux intensities are approximately identical in the two cases. A much higher power of extragalactic sources is indicative of an extragalactic cosmic-ray origin and of the existence of a universal (for all energies of protons and cosmic-ray nuclei) process that is responsible for the energy loss in the Metagalaxy and which forms the observed energy spectrum of protons and nuclei (～E ₀ ^?2.72 ). It is shown that there is no break in the energy spectrum of primary protons in the energy range 10¹⁵–10¹⁶ eV and that the break in the spectrum of extensive air showers with respect to the number of electrons is due to a change in the process of multiparticle hadron generation in the first event of extensive-air-shower production, this being confirmed by a change in the extensive-air-shower absorption length from λ_a<90 g/cm² before the break to λ_a>150 g/cm² after the break.     

Feynman scaling violation on baryon spectra in pp collisions at LHC and cosmic ray energies

A significant asymmetry in baryon/antibaryon yields in the central region of high energy collisions is observed when the initial state has nonzero baryon charge. This asymmetry is connected with the possibility of baryon charge diffusion in rapidity space. Such a diffusion should decrease the baryon charge in the fragmentation region and translate into the corresponding decrease of the multiplicity of leading baryons. As a result, a new mechanism for Feynman scaling violation in the fragmentation region is obtained. Another numerically more significant reason for the Feynman scaling violation comes from the fact that the average number of cut Pomerons increases with initial energy. We present the quantitative predictions of the Quark-Gluon String Model for the Feynman scaling violation at LHC energies and at even higher energies that can be important for cosmic ray physics.     

Models for cosmic ray interactions

Contemporary models of hadronic interactions are reviewed. Basic phenomenological approaches are compared, with an emphasizes on the predicted air shower characteristics. Special attention is payed to the remaining discrepancies between present hadronic MC generators and cosmic ray data. Finally, future prospects concerning model improvements are discussed, in particular, regarding the possibilities to discriminate between different models on the basis of accelerator or cosmic ray measurements.