STAR CLUSTER: a tracking array for gamma-ray astronomy

Summary A new type of extensive air shower array-telescope is being constructed, close to the GREX scintillator array at Haverah Park. The design of the new instrument is based on identification and measurement of individual shower particles by means of pattern recognition techniques applied to data from LST chambers above and below a thin sheet of high-Z material. Air showers will be detected in the range from 10¹⁴ eV to 10¹⁸ eV. The directions of the shower primaries will be reconstructed with an accuracy of a few tenths of a degree using triangulation between tracks of detected shower particles: >1 GeV electrons, photons and muons. Particle densities measured at the detector locations will be used to calculate shower sizes and core locations. Information about the height of production of the high-energy secondaries will be obtained for each shower. This information will be taken into account in calculating the primary energies. It will be used together with the observed muon content (ratio of muons to all particles), to draw conclusions about the nature of the primary particles. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Landau-pomeranchuk-migdal air showers initiated by ultra-high-energy neutrinos and their detection in a satellite-based experiment

The ultra-high-energy (UHE) atmospheric showers with strong influence of the Landau-Pomeranchuk-Migdal (LPM) effect (here after LPM showers) are exclusively expected to be produced by UHE neutrinos. Studies on the characteristics of the LPM showers are essentially important to discriminate neutrino shower (which produced by neutrino interaction) from hadronic shower (initiated by primary hadron). We calculate the LPM showers initiated by electrons with energies of 10¹⁸ to 10²¹ eV, using the hybrid method as exactly as possible. Reflecting the change in the air density along the shower trajectories, the variety of the LPM-shower profiles is shown in different cases for their starting points in atmosphere. Through the study of time profiles of air fluorescent photon components from the LPM showers, the detection capability of UHE neutrinos has also been investigated by the satellite-based experiment with a large acceptance, e.g., the TUS experiment.     

High energy physics in the atmosphere: phenomenology of cosmic ray air showers

The properties of cosmic rays with energies above 10⁶ GeV have to be deduced from the spacetime structure and particle content of the air showers which they initiate. In this review we summarize the phenomenology of these giant air showers. We describe the hadronic interaction models used to extrapolate results from collider data to ultra high energies, and discuss the prospects for insights into forward physics at the LHC. We also describe the main electromagnetic processes that govern the longitudinal shower evolution, as well as the lateral spread of particles. Armed with these two principal shower ingredients and motivation from the underlying physics, we provide an overview of some of the different methods proposed to distinguish primary species. The properties of neutrino interactions and the potential of forthcoming experiments to isolate deeply penetrating showers from baryonic cascades are also discussed. We finally venture into a terra incognita endowed with TeV-scale gravity and explore anomalous neutrino-induced showers.     

Pulsars as the most probable sources of ultrahigh-energy cosmic rays

The arrival directions of ultrahigh-energy extensive air showers detected at the Yakutsk extensive air shower array are considered. The maxima revealed in the distribution of the arrival directions of showers and doublets are found to correlate with the coordinates of pulsars located in the Galactic plane. It is shown that the three showers detected at the Yakutsk extensive air shower with the highest energies E > 10²⁰ eV correlate with the nearest pulsars.     

On the sensitivity of the spatial-angular distribution of the Cherenkov light in extensive air showers to the mass composition of primary cosmic rays with energies of 10<Superscript>15</Superscript>–10<Superscript>16</Superscript> eV

This paper analyses the possibility of separating distinct groups of nuclei of primary cosmic rays with energies of 10¹⁵–10¹⁶ eV from the data on the spatial-angular distribution of Cherenkov light in extensive air showers. The paper shows that using an array of a few (3–4) telescopes with a moderately sized angular cell ∼0.5° placed at a distance ∼100 m from one another, one can achieve almost complete separation of the showers initiated by these nuclei (the Bayesian classification error is a few percentage points for the case of separating primary protons and nitrogen nuclei). The authors propose new parameters of the angular Cherenkov image that can greatly enhance the separability of the shower classes as compared to the approach based on the traditional parameters.     

Possible observations of new physics in ultrahigh-energy cosmic rays

The muon lateral structure functions in giant air showers induced by primary photons have been simulated with the help of original codes. Particularly, the densities of muons with energies above 0.5 and 1 GeV at a distance of 1000 m from the shower core have been estimated for gamma-induced showers of various energies. A comparison with the results of calculations for hadronic showers shows a considerable deficit of muons in the gamma-induced showers. The density of muons at a distance of 1000 m from the shower core happened to be ≳ 10 times larger for the hadronic showers. Some possible constraints of the source models with superheavy-dark-matter particles and topological defects are discussed. The text was submitted by the authors in English.     

Mass Composition of Cosmic Rays with Energies above 1017 eV According to the Data from the Muon Detectors of the Yakutsk EAS Array

The lateral distribution of muons in extensive air showers with energies above 1017 eV detected by underground scintillation detectors with a threshold of 1.0 GeV at the Yakutsk array in 1986–2016 has been analyzed. The experimental data on the muon flux density at a distance of 300 m from the shower axis have been compared to the calculations within various models of hadron interactions at ultrahigh energies. The experimental data are in the best agreement with the QGSJet01 and QGSJet II-04 models. The mass composition of cosmic rays in the energy range of (1–30) × 10¹⁷ eV changes from middle nuclei to a purely proton composition.

     

Upper limit on the photon fraction in highest-energy cosmic rays from AGASA data

A new method to derive an upper limit on photon primaries from small data sets of air showers is developed which accounts for shower properties varying with the primary energy and arrival direction. Applying this method to the highest-energy showers recorded by the AGASA experiment, an upper limit on the photon fraction of 51% (67%) at a confidence level of 90% (95%) for primary energies above 1.25 x 10(20) eV is set. This new limit on the photon fraction above the Greisen-Zatsepin-Kuzmin cutoff energy constrains the -burst model of the origin of highest-energy cosmic rays.     

Muon content of ultrahigh-energy air showers: Yakutsk data versus simulations

A sample of 33 extensive air showers (EASs) with estimated primary energies above 2 × 10¹⁹ eV and high-quality muon data recorded by the Yakutsk EAS array is analyzed. The observed muon density is compared event-by-event to that expected from CORSIKA simulations for primary protons and iron using SIBYLL and EPOS hadronic interaction models. The study suggests the presence of two distinct hadronic components, “light” and “heavy.” Simulations with EPOS are in good agreement with the expected composition in which the light component corresponds to protons and the heavy component to iron-like nuclei. With SIBYLL, simulated muon densities for iron primaries are a factor of ∼ 1.5 less than those observed for the heavy component for the same electromagnetic signal. Assuming a two-component proton-iron composition and the EPOS model, the fraction of protons with energies E > 10¹⁹ eV is 0.52_−0.20^+0.19 at the 95% C.L. The text was submitted by the authors in English.     

Changes in the chemical composition of primary cosmic radiation at ultrahigh energies

The signals from particles of extensive air showers in the energy region of 10¹⁷–10²⁰ eV in both the surface and underground scintillation detectors of the Yakutsk array are calculated using the CORSIKA 6.616 and GEANT4 software packages and compared with experimental data. It is shown that a transition from a heavy primary composition to proton primaries at energies (1–2.6) × 10¹⁸ eV and from primary protons again to heavy primaries at energies above 1.3 × 10¹⁹ eV might be observed.     

Transverse-momentum-ordered showers and interleaved multiple interactions

We propose a sophisticated framework for high-energy hadronic collisions, wherein different QCD physics processes are interleaved in a common sequence of falling transverse-momentum values. Thereby phase-space competition is introduced between multiple parton-parton interactions and initial-state radiation. As a first step we develop new transverse-momentum-ordered showers for initial- and final-state radiation, which should be of use also beyond the scope of the current article. These showers are then applied in the context of multiple interactions, and a few tests of the new model are presented. The article concludes with an outlook on further aspects, such as the possibility of a shower branching giving partons participating in two different interactions.Received: 26 August 2004, Revised: 14 October 2004, Published online: 11 January 2005     

The proton-air cross-section at 1016 eV

Summary A study of the Čerenkov light lateral distribution function for cosmic-ray showers with energies of about 10¹⁶ eV has been used to determine the distribution of depths of shower maximum at these energies. This distribution has an exponential tail due to fluctuations in the depths of early interactions of the proton primary component. The form of this tail may be used to infer an inelastic proton-air cross-section of (590±70) mb at ≈10¹⁶ eV.

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Riassunto Si usa uno studio della distribuzione laterale della luce di Čerenkov per sciami cosmici con energie di circa 10¹⁶ eV per determinare la distribuzione di profondità del massimo degli sciami a queste energie. Questa distribuzione ha una coda esponenziale dovuta a fluttuazioni nelle profondità delle prime interazioni della componente protonica delle primarie. La forma di questa coda si può usare per inferire una sezione d'urto anelastica protone-aria di (590±70) mb a ≈10¹⁶ eV.

     

Neutrino cross sections and future observations of ultrahigh-energy cosmic rays

We show that future detectors of ultrahigh-energy cosmic-ray neutrinos will be able to measure neutrino-nucleon cross section, sigma(nu N), at energies as high as 10(11) GeV or higher. We find that the flux of upgoing charged leptons per unit surface area produced by neutrino interactions below the surface is inversely proportional to sigma(nu N). This contrasts with the rate of horizontal air showers (HAS) due to neutrino interactions in the atmosphere, which is proportional to sigma(nu N). Thus, by comparing the HAS and upgoing air shower rates, the neutrino-nucleon cross section can be inferred. Taken together, upgoing and horizontal rates ensure a healthy total event rate, regardless of the value of sigma(nu N).     

Small shower CORSIKA simulations

Extensive Air Showers (EAS) induced by cosmic ray particles of very low energies, owing to the significantly steep cosmic ray energy spectrum, dominate the secondary particle flux measured by single detectors and small shower arrays. Such arrays connected in extended networks can be used to determine potentially interesting spatial correlations between showers, which may shed new light on the nature of ultra high-energy cosmic rays. The quantitative interpretation of showers recorded by small local arrays requires a methodology that differs from that used by ordinary large EAS arrays operating in the "knee" region and above. We present "small EAS generator," a semi-analytical method for integrating cosmic ray spectra over energies of interest and summing over the mass spectra of primary nuclei in arbitrary detector configurations. Furthermore, we provide results on the EAS electron and muon fluxes and particle density spectra.     

Observation of double extensive air showers

Double extensive air showers were studied at the Tien Shan high-mountain scientific station of the Lebedev Physical Institute using two different installations. One measured the electron-photon shower component, the other measured Cherenkov radiation. Double showers separated by a time interval of ～100 ns were detected by both setups. The frequency of the occurrence of such showers in each setup is analyzed. It is shown that these frequencies are identical when observing vertical showers (the zenith angle ? < 60°).     

Wavelet analysis of angular distributions of secondary particles in high-energy nucleus-nucleus interactions: Irregularity of particle pseudorapidity distributions

Experimental data on interactions of sulfur and oxygen nuclei with photoemulsion nuclei at energies of 200 and 60 GeV/nucleon are analyzed with the help of a continuous wavelet transform. Irregularities in pseudorapidity distributions of narrow groups of the secondary shower particles in these interactions are observed upon application of the second-order derivative of a Gaussian as a wavelet. The irregularities can be interpreted as the existence of preference emission angles of groups of particles. Such an effect is expected during emission of Cherenkov gluons in nucleus-nucleus collisions. Some of the positions of the observed peculiarities on the pseudorapidity axis coincide with those found by Dremin et al. (I. M. Dremin et al., Phys. Lett. B 499, 97 (2001)).     

Cosmic-ray muons at ultrahigh energies

Fluxes of cosmic-ray muons were estimated over the energy range extending up to 10¹⁰ GeV. Data on the production of pions; kaons; η, η′, ρ, ω, and ϕ mesons; charmed particles; and J/ψ mesons from accelerator experiments devoted to studying interactions between nucleons and nuclei of air atoms up to nucleon energies of about 2 × 10⁴ GeV were used in respective calculations. At higher energies, use was made of the results obtained by calculating cross sections for the production of charmed particles and J/ψ mesons on the basis of QCD models. It is shown that, in interpreting experimental data on extensive air showers, the production of both charmed particles and J/ψ mesons in the Earth’s atmosphere must be taken into account.     

Anomalous extensive air showers of ultrahigh energies and their arrival directions

Extensive air showers (EASs) of energy above 8×10¹⁸ eV observed from 1974 to 1995 on the Yakutsk EAS array are analyzed. Showers without muonic component are found. From the arrival directions of these showers, two clusters were found, one of which coincides, within the error bars, with a pulsar in the Milky Way Galaxy.