Cascade showers in the NEVOD Cherenkov water detector

A technique for measuring the cascade shower energy in the NEVOD Cherenkov water detector with a spatial lattice of quasi-spherical modules is discussed. The technique allows the number of cascade particles that move near the shower axis to be reconstructed on the basis of analysis of response amplitudes of triggered photomultiplier tubes. The technique of cascade-curve reconstruction was applied to cascade showers generated by near-horizontal high-energy muons extracted by means of the DECOR coordinate-tracking detector arranged around the Cherenkov water detector. The first results of measuring the energy spectrum of cascade showers of 10–1000 GeV are presented.     

Energy spectrum of cascade showers generated in water by near-horizontal muons

We discuss measuring cascade shower energy using the NEVOD Cherenkov water detector with a spatial lattice of quasi-spherical modules (QSMs). Dense QSM spacing makes it possible to reconstruct a number of cascade particles along the shower axis from the PMT response amplitude. Our cascade curve reconstruction technique is applied to showers generated by near-horizontal high-energy muons selected using the DECOR coordinate detector deployed around NEVOD. The first results from cascade energy spectrum measurements are reported.     

A new method for observing the shower cascade profile at the Yakutsk EAS array

An empirical approach is presented for reconstruction of the extensive air shower (EAS) cascade curve according to data of the Cherenkov track detector. The proposed method, unlike conventional ones, is based on experimentally measured parameters and on calculated values which weakly depend on the model of shower development.     

Spatiotemporal structure of pulses in detectors of Cherenkov light of extensive atmospheric showers

We calculated the pulses of the Cherenkov light of extensive atmospheric showers in Cherenkov radiation detectors at the Yakutsk array in the framework of the QGSJET-II model. It is shown that the calculated width of a pulse of Cherenkov light in a vertical proton-induced shower of energy of 10¹⁸–10²⁰ eV increases from 50 ns at a distance of 200 m from the shower axis to 700 ns at a distance of 1 km.     

Orientation dependences of the response of an electromagnetic spectrometer with oriented crystal converter

The experimental results of the study of orientation dependences of the response of a composite Cherenkov shower spectrometer with a converter made of a 1-mm tungsten crystal oriented along the 〈111〉 axis at an electron energy of 28 GeV and two converter temperatures, 293 and 77 K, are presented. The parameters of the cascade curve of the shower development are varied depending on the orientation angle and crystal temperature. It is found that there is a point S in the cascade curve of the shower development in the spectrometer, at which all cascade curves intersect at any converter orientation. The position of this point in the spectrometer depth depends on the converter temperature.     

Energy dependence of the response of an electromagnetic spectrometer with oriented crystal converter

The experimental results of the study of the dependence of the response of a composite Cherenkov shower spectrometer with a converter made of 〈111〉 tungsten crystal 1 mm thick on the electron energy of 26, 28, and 31 GeV are presented. It is found that the cascade curve maximum position and the energy release at the maximum of the cascade curve of shower development in the spectrometer with both oriented or misoriented converters have the logarithmic and proportional dependences on electron energy.     

Determining the primary cosmic ray energy from the total flux of Cherenkov light measured at the Yakutsk EAS array

We present a method for determining the energy of the primary particle that generates an extensive air shower (EAS) of comic rays based on measuring the total flux of Cherenkov light from the shower. Applying this method to Cherenkov light measurements at the Yakutsk EAS array has allowed us to construct the cosmic ray energy spectrum in the range 10¹⁵ ? 3 × 10¹⁹ eV.     

Estimation of the parameters of the cascade curve of electromagnetic shower development in a spectrometer with oriented crystal converter

Based on the experimental results on the development of electromagnetic showers from 26-GeV electrons in misoriented and oriented along the 〈111〉 axis tungsten crystals 2.7, 5.8, 8.4mm thick and then in a composite Cherenkov shower spectrometer, the parameters of the cascade curve of shower development in a spectrometer with 1-mm tungsten crystal converter were estimated.     

Methods for estimating the energy of extensive air showers

A multilevel scheme for calculating estimates of the energy of extensive air showers on the basis of signals in different detectors is considered. The numerical energy estimates at specified values of signals in scintillation detectors are smaller than the experimental ones by a factor of about 1.6. The results of the calculation confirmed that the total flux of Cherenkov light is proportional to the shower energy. The flux of fluorescent light generated within 100 m from the shower core is due to only 60% of the total energy.     

Restoration of parameters of high-energy cascades in Cherenkov water calorimeter with a dense array of quasispherical modules

A problem concerning the restoration of the parameters of a cascade shower with an unknown axis originating by muons in a Cherenkov water calorimeter is considered. A method for estimating the direction and geometric position of the cascade’s axis, which is based on the analysis of responses of quasispherical modules, and the criteria of selection of the events with cascades among the events with a large energy liberation are proposed. The method and the criteria are tested on events with cascades generated by near-horizontal muons of high energies detected by a DECOR coordinate-track detector. The preliminary results of measurements of the energy spectrum of cascade showers are presented.     

Simulation of propagating EAS Cherenkov radiation over the ocean surface

We present computing results of the Cherenkov light propagation in the air and water from an extensive air shower (EAS) over the ocean. Limits on the zenith angles of the showers, for which the registration of the flash of reflected photons by the space-detector is possible, are analyzed with consideration for waves on the ocean surface.     

Violation of the coherence of radio waves induced by a cascade shower in the lunar regolith

It has been shown that small fluctuations of the refractive index of the lunar regolith owing to, e.g., a nonuniform density distribution, give rise to the loss of the coherence of a Cherenkov radio pulse induced by a cascade shower from an ultrahigh-energy particle and to a strong decrease in the spectral density of the radio signal. This can be one of the causes of why no events from ultrahigh-energy cosmic particles on the surface of the moon have been detected.     

Geometry and optics calibration of WFCTA prototype telescopes using star light

The Large High Altitude Air Shower Observatory (LHAASO) project is proposed to study high energy gamma ray astronomy (40 GeV-1 PeV) and cosmic ray physics (20 TeV-1 EeV). The wide field of view Cherenkov telescope array, as a component of the LHAASO project, will be used to study the energy spectrum and composition of cosmic rays by measuring the total Cherenkov light generated by air showers and the shower maximum depth. Two prototype telescopes have been in operation since 2008. The pointing accuracy of each telescope is crucial for the direction reconstruction of the primary particles. On the other hand, the primary energy reconstruction relies on the shape of the Cherenkov image on the camera and the unrecorded photons due to the imperfect connections between the photomultiplier tubes. UV bright stars are used as point-like objects to calibrate the pointing and to study the optical properties of the camera, the spot size and the fractions of unrecorded photons in the insensitive areas of the camera.     

Parametric analysis of Cherenkov light LDF from EAS in the range 30–3000 TeV for primary gamma rays and nuclei

A simple “knee-like” approximation of the Lateral Distribution Function (LDF) of Cherenkov light emitted by EAS (extensive air showers) in the atmosphere is proposed for solving various tasks of data analysis in HiSCORE and other wide angle ground-based experiments designed to detect gamma rays and cosmic rays with the energy above tens of TeV. Simulation-based parametric analysis of individual LDF curves revealed that on the radial distance 20?500 m the 5-parameter “knee-like” approximation fits individual LDFs as well as a mean LDF with a very good accuracy. In this paper we demonstrate the efficiency and flexibility of the “knee-like” LDF approximation for various primary particles and shower parameters and the advantages of its application to suppressing proton background and selecting primary gamma rays.     

Longitudinal development of electromagnetic showers in directional spectrometer

The length of the longitudinal development of the electromagnetic shower induced by electrons with an energy of 26 GeV in a directional spectrometer consisting of a crystalline tungsten converter oriented along the ??111?? axis and a composite Cherenkov shower spectrometer is shorter in comparison with the length of the standard shower development by 20?C30% at a converter thickness from 2.7 to 8.4 mm.     

On the geomagnetic mechanism of the radiation of an extensive air shower

The radiation field of the elementary particles of an extensive air shower in the geomagnetic field has been examined. According to the solutions of Maxwell’s equation for an electron (positron) taking into account ionization losses, the radiation of the shower is determined only by the bremsstrahlung and geomagnetic mechanism. The Cherenkov component of radiation is almost absent.     

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.     

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.     

On the surface cascade radio emission escape into vacuum through the rough lunar surface

The radio emission escape of an almost horizontal cascade through the rough lunar surface into vacuum is considered. The point approximation is accepted for the shower disk size, taking into account its evolution along the cascade track. The lunar surface is assumed to be flat, but having a single perturbation such as a cylindrical “hill” perpendicular to the shower disk motion direction. The perturbation is not assumed to be small. Diffraction associated with the wave phase progression and variations of the slope of the normal to the rough surface for various rays forming the total wave field in vacuum is taken into account.