T. M. Roganova

Upper limit on the ultrahigh-energy photon flux from AGASA and Yakutsk data

We present the interpretation of the muon and scintillation signals of ultrahigh-energy air showers observed by AGASA and Yakutsk extensive air shower array experiments. We consider case-by-case ten highest-energy events with known muon content and conclude that at the 95% confidence level none of them was induced by a primary photon. Taking into account statistical fluctuations and differences in the energy estimation of proton and photon primaries, we derive an upper limit of 36% at a 95% confidence level on the fraction of primary photons in the cosmic-ray flux above 10{sup 20} eV. This result disfavors the Z-burst and superheavy dark-matter solutions to the Greisen-Zatsepin-Kuzmin-cutoff problem.

The composition of the primary particles at energies 3 ×10 17 -3 ×10 19 eV observed at the Yakutsk array

Signals in the surface and underground scintillation detectors of the Yakutsk array from particles of extensive air showers and a fraction of muons at 600 m from the vertical shower axis have been simulated. Calculations have been carried out in terms of QGSJET-II and Gheisha-2002d models with the help of the CORSIKA 6.616 and GEANT4 codes at energies 3×1017–3×1019 eV. A comparison of the results of these simulations with data observed at the Yakutsk array shows rather heavy composition of the primary radiation in this energy region. But it was shown that the number of muons is underestimated by ~15% if the QGSJET-II model was used at energies above 100 GeV and by ~ 10% if the Gheisha-2002d model was used at energies below 100 GeV. Besides, signals in the surface and underground detectors from a muon differ by 3%. A comparison of the results with these corrections taken into account with data favors rather a light (maybe a proton-dominated) composition of the primary radiation in the energy region of 2.3×1018–1.14×1019 eV. In the energy interval of 3×1017–2.3×1018 eV, the composition is heavier. At energies above 1.14×1019 eV, a composition may also be heavier as illustrated by a trend of data.

Employing Cherenkov radiation and fluorescence light in calibrating the energy of giant air showers

A classic procedure for estimating the energy of giant air showers in terms of the parameter s(600) (density of energy deposition in a scintillator at a distance of 600 m from the shower axis) is analyzed on the basis of the model of quark-gluon strings. A simulation of the signal s(600) by means of the CORSIKA code leads to estimates of energy that are approximately 1.6 times lower than those adopted at the Yakutsk array. Estimates of energy on the basis of Cherenkov radiation agree with experimental data within the errors. Calculations of the distributions of energy deposited in the atmosphere indicate that more than 20% of this energy can be deposited at distances in excess of 100 m from the shower axis.

The new Tien-Shan Atmospheric Čerenkov Telescope (TACT). Contemporary status: all-particle spectrum measured

Abstract Results for the primary cosmic ray energy spectrum at 100–1000 TeV, data on the lateral distribution function for Cerenkov light of EAS and curvature of Cerenkov photon front are presented. Measurements were carried out using an array for observation of discrete gamma-sources in the TeV region.

Method for measuring the PCR proton spectrum in the energy range of > 1016 eV

Criteria for selecting proton events among the total sequence of events from primary nuclei of cosmic rays with zenith angles θ < 20° are analyzed in the energy region of E0 ≈ 1016 eV. These criteria are concretized for the case of the SPHERE-2 experiment geometry. The QGSJET-I and QGSJET-II model calculations show that the criteria based on the shape of the transverse distribution of Cherenkov light allow detection of more than 10% of proton events and rejection of 99% nuclear events.

Results on the primary CR spectrum and composition reconstructed with the SPHERE-2 detector

First preliminary results of the balloon-borne experiment SPHERE-2 on the all-nuclei primary cosmic rays (PCR) spectrum and primary composition are presented. The primary spectrum in the energy range 1016–5 1017 eV was reconstructed using characteristics of Vavilov-Cherenkov radiation of extensive air showers (EAS), reflected from a snow surface. Several sources of systematic uncertainties of the spectrum were analysed. A method for separation of the primary nuclei groups based on the lateral distribution function (LDF) steepness parameter is presented. Preliminary estimate of the mean light nuclei fraction f30-150 at energies 3 1016–1.5 1017 eV was performed and yielded f30-150 = (21±11) %.

Event-by-event study of CR composition with the SPHERE experiment using the 2013 data

We present an event-by-event study of cosmic ray (CR) composition with the reflected Cherenkov light method. The fraction of CR light component above 5 PeV was reconstructed using the 2013 run data of the SPHERE experiment which observed optical Vavilov-Cherenkov radiation of extensive air showers, reflected from snow surface of Lake Baikal. Additionally, we discuss a possibility to improve the elemental groups separability by means of multidimensional criteria.

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 knee in the primary-cosmic-ray spectrum, observed in the hadron component of extensive-air-shower cores at the mountain level

The spectra of the hadron component in extensive-air-shower (EAS) cores detected at the Tien Shan high-altitude scientific station of the Lebedev Institute of Physics, Russian Academy of Sciences, have been analyzed. Simulation was performed using the CORSIKA code within the QGSJET01 and QGSJET02 models under different assumptions about the primary-cosmic-ray (PCR) spectrum in the knee region. It is shown that the QGSJET01 model underestimates the energy of the hadron component of EAS cores at the mountain level. It is also shown that a pronounced knee in the experimental spectrum suggests a sharp (dγ ∼ 1.5) change in the exponent of the proton spectrum slope at an energy of about 5 PeV.

Search for neutrino oscillations vμ → vτ in CERN → Gran Sasso high-energy neutrino beam (the OPERA experiment)

The main purpose of the OPERA experiment is the direct observation of neutrino oscillations (vμ → vτ) in the vμ beam from the CERN accelerator through the direct detection of τ leptons in nuclear emulsions at the Gran Sasso National Underground Laboratory. Some aspects of the use of the Russian PAVICOM facility for processing and analyzing the data obtained from the OPERA experiment are discussed.