Simulation of an experiment on detecting ultra-high-energy particles with regard to the structure of the lunar soil surface layer

The feasibility of using the lunar orbital radio detector to detect radio signals from cascades initiated by ultra-high-energy cosmic rays interacting with the lunar regolith is studied. Simulation by the Monte Carlo method demonstrates that, with the regolith thickness randomly distributed in the range 2–12 m, the detection of radio signals reflected from the lower boundary of the regolith (for particle energies W ≥ 10²⁰ eV) increases the number of valid events severalfold. The additional contribution due to the reflected radio-frequency radiation greatly enhances the scientific potential of experiments with the lunar orbital radio detector.     

Radio-frequency component of transient radiation of an extensive air shower

The mechanism of radio emission induced by the transient radiation of oppositely charged particles from an extensive air shower in the geomagnetic field was studied for the first time. For showers with an energy of ∼10²² eV, the electric field strength at a distance of 500 km from the shower axis was found to be 60 μV/mMHz. Such showers attain their maximum at sea level. The spectral intensity of emission is maximum at frequencies of about 1 MHz (at these frequencies, the intensity of atmospheric disturbances is minimum). These specific features of radio emission can be used in experiments for radio detection of high-energy cosmic rays. An experimental setup of such detection is suggested.     

Extragalactic electromagnetic cascades as a possible instrument for the study of background radio emission

We analyzed the diffuse gamma-ray emission generated in the interactions between cosmic rays of ultrahigh energies and the background radiation in extragalactic space. The intensity of gamma-ray emission was calculated within a simplified model for energies E ≈ 10¹⁴ eV in different assumptions concerning the cosmic ray sources with the use of different estimates of nonthermal background radiation. It was shown that the gamma-ray radiation intensity in this energy range depends on the background radio emission and that under different assumptions concerning the radio background it can differ tens of times. It was concluded that gamma-ray emission can serve as a test for the models of background radio-frequency radiation.     

Astroparticle physics with high energy neutrinos: from AMANDA to IceCube

Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of 10²⁰ eV and 10¹³ eV, respectively. The puzzle of where and how Nature accelerates the highest energy cosmic particles is unresolved almost a century after their discovery. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the science reach of its extension, IceCube. Similar experiments are under construction in the Mediterranean. Neutrino astronomy is also expanding in new directions with efforts to detect air showers, acoustic and radio signals initiated by super-EeV neutrinos. The outline of this review is as follows:

Introduction

Why kilometer-scale detectors?

Cosmic neutrinos associated with the highest energy cosmic rays

High energy neutrino telescopes: methodologies of neutrino detection

High energy neutrino telescopes: status

     

Low-frequency radio emission induced by the coherent magneto-bremsstrahlung of charged particles of an extensive air shower

A previously unknown coherent low-frequency (0<ν<50 kHz) component of radio emission of an extensive air shower in the geomagnetic field is reported. This type of emission induces a high-intensity field (∼200 μV/m MHz at a distance of 100 km from the shower axis). This emission mechanism is believed to be responsible for the previously observed high-intensity radio emission of the shower at low frequencies. The possibility of radio detection of ultrahigh-energy (W ₀>10²¹ eV) cosmic rays is considered.     

Simulations of radio emission from ultrahigh-energy extensive air showers

The radio emission from extensive air showers with energies up to 10¹⁷ eV has been calculated. The calculated lateral distribution of the radio emission is in good agreement with the LOPES-10 experimental data.     

Radio emission of extensive air showers as a method for detecting ultra-high energy cosmic rays

Recording radio emission from extensive air showers (EASs) is considered now as a new promising method for detecting ultra-high energy (E ₀ > 5 × 10¹⁶ eV) cosmic rays. The results of calculation of EAS radio emission at frequencies from 40 to 80 MHz in the EAS energy range E ₀ = 10¹⁴–10¹⁷ eV are reported here, and the possibilities of determining EAS parameters from the radio emission lateral distribution are discussed.     

Possible attenuation of the radio signal from the cascade in solid medium at energies above 1020 eV

It was shown that the effect of plasma production during solid medium ionization by a developing cascade can shield excess-charge radiation in the radio range used for detecting particles at energies higher than 10²⁰ eV. Such a shielding effect is significant in Antarctic ice and is insignificant for lunar regolith. Hence, the LORD experiment on detection of cascades from ultrahigh-energy cosmic rays and neutrinos from circumlunar spacecrafts retains the capability of measurements up to the energies of 10²³ eV.     

On the attenuation of radio Cherenkov radiation from a cascade in a solid medium at ultrahigh energies

It is shown that the effect of the formation of electron-hole plasma during ionization of a solid mediumby a cascade developing in it can shield charge-excess Cherenkov radiation in the radio range used for detecting particles by radio detectors at energies above 10²⁰ eV. Such a shielding effect is strong in pure Antarctic ice and is weaker in lunar regolith; hence, the LORD experiment on the detection of cascades from ultrahigh-energy cosmic rays and neutrinos by circumlunar apparatuses retains the possibility of detecting particles to energies of ∼3 · 10²⁰ eV.     

Radio emission from extensive air showers as a method for cosmic-ray detection

At the present time, radio emission from extensive air showers (EASs) is being considered as a new promising method for detecting cosmic rays of energy in the region E ₀ > 5 × 10¹⁶ eV. Radio emission from an EAS whose development is simulated by the Monte Carlo method is calculated here. The field of radio emission from an EAS is calculated on the basis of two representations of a shower: that as a set of individual particles and that as a continuous set of currents. The sensitivity of radio emission to EAS parameters in the frequency range 10–100 MHz is investigated. The results can be used to analyze experiments that being presently performed (CODALEMA and LOPES) and those that are being planned for the future.     

Diffuse extragalactic very-high-energy γ rays

γ Rays with energies E > 4 × 10¹⁹ eV, which are produced upon interactions of cosmic rays with the background radiation in intergalactic space, have been analyzed. The intensity of such γ rays is calculated under different assumptions about the cosmic-ray sources and using different estimates of the nonthermal background radio emission.     

Energy spectrum and mass composition of primary cosmic rays at energies 10<Superscript>15</Superscript>–10<Superscript>18</Superscript> eV

Data on muon and electron components of extensive air showers (EAS) (obtained with the EAS MSU array) were used to derive the primary cosmic ray (PCR) mass composition. It is shown that for energies beyond the knee at energy 3 × 10¹⁵ eV the abundance of heavy nuclei increases with energy. But at energies above 10¹⁷ eV the abundance of light nuclei starts to grow. The primary cosmic ray spectrum in the range 10¹⁵–10¹⁸ eV is analyzed. It is shown that at energies above 10¹⁷ eV the additional component appears and it differs from the bulk of Galactic cosmic rays generated by shocks in SN remnants.     

The extensive air shower muon number spectrum beyond the knee in the cosmic-ray energy spectrum

The extensive air shower (EAS) muon number spectrum is obtained with increased statistics using the central muon detector of the EAS MSU array, which records muons with energies above 10 GeV. The dependence of the mass composition of primary cosmic rays on the energy is considered. The conclusion is confirmed that for energies from 3 × 10¹⁵ eV (the primary energy spectrum knee) up to 10¹⁷ eV a change in the composition associated with an increase in the proportion of heavy nuclei occurs; however, after the energy of 10¹⁷ eV, the proportion of heavy nuclei begins to decrease and the composition becomes lighter. A comparison with similar data from other experiments is conducted. The existence of an additional component of cosmic rays is confirmed; earlier an indication of its presence was derived from data on the EAS electron number spectrum.     

Prospects of experimental measurements at LHC to better understand cosmic ray induced air showers

In a few years, the LHC will provide proton-proton and nucleus-nucleus collisions at the highest c.m. energies available so far in the laboratory, up to 14 TeV in the case of proton-proton collisions. This regime corresponds to energies of cosmic rays of about 10¹⁷ eV, above the so-called “knee region” in the cosmic-ray flux. A summary of main features of the machine will be presented, concentrating on the various running scenarios foreseen. An overview of the approved experiments and their baseline coverage, as well as possibilities for extensions, will be given. The latter could provide a better coverage of the forward region (small angles with respect to the beam direction) and might give valuable information to help in our understanding of extended air showers induced by cosmic rays in the atmosphere of the Earth.     

Air shower universality in the energy range of 1014 to 1022 eV

Universality in the development of air showers initiated by photons and the nuclei of cosmic rays is studied over a wide range of energies (10¹⁴–10²² eV). The scaling invariance of the lateral distribution of electrons and the universal relationship between a cascade’s age and radial scaling parameter (the root-meansquare radius of the electron component) are found to remain valid up to ultimate high energies with allowance for the Landau-Pomeranchuk-Migdal effect and interaction with the geomagnetic field. Possible applications of universality for matching, reanalyzing, and verifying the validity of data from different experiments, and for reducing the effect of the nuclear interaction model’s uncertainty on estimates of the mass composition of primary cosmic rays, are discussed.     

Study of the energy spectrum and mass composition of primary cosmic rays in the energy range of 10<Superscript>18</Superscript>–10<Superscript>20</Superscript> eV using a balloon setup in antarctica (SPHERE-antarctica project)

An Antarctic balloon experiment for measuring the energy spectrum and elemental composition of cosmic rays in the ultrahigh-energy range (10¹⁸–10²⁰) eV is proposed. Scientific equipment will measure fluorescence caused by an extensive air shower formed in the atmosphere by an ultrahigh energy particle and Cherenkov light of this shower reflected from a snow surface. It is assumed that the balloon will fly in the circumpolar orbit in Antarctica at a height of ~25 km for (2–3) winter (in the Southern Hemisphere)months. For this time, ~3000 events caused by particles with energies above 10¹⁸ eV and (200–300) events caused by particles with energies above 10¹⁹ eV will be detected.     

Recording of ultrahigh-energy astrophysical neutrinos

This review is devoted to the problems of recording ultrahigh-energy neutrinos produced in distant astrophysical sources and during the decay of supermassive particles. Prospects for the detection of neutrino fluxes are considered based on peculiarities of the propagation and interaction of ultrahigh-energy neutrinos. The operating and planned facilities designed to investigate neutrinos from various sources are described: neutrino telescopes recording neutrino interactions in natural water and ice volumes; ground-based arrays of detectors and optical telescopes onboard orbital space stations capable of detecting neutrino-triggered horizontal air showers. Instruments based on new principles of recording neutrinos with extremely high energies are considered: radio telescopes designed to observe Cherenkov radio emission from neutrino cascades originating in such radio-transparent natural environments as the atmosphere, salt domes, ice packs, and lunar regolith; underwater acoustic detectors. It is shown that putting new facilities into operation will allow neutrinos from most of the known astrophysical sources with energies differing by more than ten orders of magnitude, from 10¹² to 10²²–10²⁴ eV, to be recorded.     

Radio signals from extensive air showers with the energies <Emphasis Type="Italic">E</Emphasis> <Subscript>0</Subscript> ≥ 10<Superscript>19</Superscript> eV according to data from the Yakutsk extensive air shower array

A radio instrument and results obtained from the measurements of the 32-MHz radio signal from particles of extensive air showers (EASs) with energies E₀ ≥ 1×10¹⁹ eV are reported in brief. The data were obtained at the Yakutsk EAS array in 1987–1989 (the first series of measurements) and in 2009–2014 (new series of measurements). The radio signal from EASs with energies above 10²⁰eV was detected at the Yakutsk EAS array for the first time, including the shower with the record energy of ~2×10²⁰ eV for the Yakutsk EAS array.     

Hybrid method for detecting cascades produced by ultrahigh-energy cosmic particles using a circumlunar satellite

A hybrid method for detecting cosmic rays and neutrino cascades using the radio method and the conventional method for detecting cascade particles was proposed. Cascades produced in the lunar soil near the surface by ultrahigh-energy cosmic rays and neutrinos in the energy range of 1 GeV–100 TeV, coming from above at different angles, were calculated. The calculated energy and angular distributions were extrapolated to the energy region of 10²⁰ eV. Using these results, the detection threshold was estimated as 10²⁰ eV which is approximately identical to the threshold for the radio detector previously considered by the authors.     

Is it possible to determine the chemical composition of cosmic rays in the “LORD” lunar experiment?

The results of the simulation of cascade radio emission from ultrahigh-energy cosmic rays in the LORD lunar experiment using circularly polarized antennas are presented. It is shown that based on the characteristics of radio emission caused by cascades from protons and iron nuclei in lunar regolith and escaped into vacuum it is impossible to distinguish these cascades in the primary energy region above 10²⁰ eV.