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.     

Spatial distribution of Cherenkov light from cascade showers in water

The spatial distribution of the Cherenkov light generated by cascade showers is analyzed using the NEVOD Cherenkov water detector. The dependence of the Cherenkov light intensity on the depth of shower development at various distances from the shower axis is investigated for the first time. The experimental data are compared with the Cherenkov light distributions predicted by various models for the scattering of cascade particles.     

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.     

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.     

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.     

HYDRA hydroacoustic antenna in the NEVOD experimental complex

The main characteristics of the HYDRA hydroacoustic antenna intended for the detection of signals generated by cores of extensive air showers in a water Cherenkov detector involved in the NEVOD experimental complex are considered. Primary attention is focused on the calibration of antenna sensors and on the selection of an optimum trigger that ensures an effective detection of acoustic signals generated by cores of extensive air showers in the water volume of the Cherenkov detector.     

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.     

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.     

Performance of the muon detector A under TIBET Ⅲ array

In order to observe gamma rays in the 100 TeV energy region, the 4500 m² underground muon detector array using water Cherenkov technique is constructed, forming the TIBET Ⅲ+MD hybrid array. Because the showers induced by primary gamma rays contain much fewer muons than those induced by primary hadrons, significant improvement of the gamma ray sensitivity for TIBET Ⅲ+MD array is expected. In this paper, the design and performance of the MD-A detector with large Tyvek bag is 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.     

Possibility of using satellite-based detector for recording the Cherenkov light from ultrahigh-energy extensive atmospheric shower penetrating into ocean water

Various components of Cherenkov radiation are calculated which occur during development of a shower with a primary energy of 10²⁰ eV above the ocean surface. It is shown that, under conditions of the TUS experiment, a flare of the reflected Cherenkov photons at the end of the fluorescence track can be identified in showers with zenith angles up to 20°.     

Investigating hadronic cores of exstensive air showers at the CARPET-2 array

Characteristics of the hadronic component of exstensive air shower (EAS) trunks are investigated at the CARPET-2 array of the Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences. In this work, we study showers with axes that located within its muon detector (MD). We discuss the procedure for selecting such showers in our experiment. The relationship between the number of thermal neutrons detected by heat detectors installed in the muon detector’s tunnel and the total energy of a cascade generated by hadrons in the magnetic detector’s absorbent matter is 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.     

Study of cascade showers generated by near-horizontal muons in the water Cherenkov detector with a dense array of optical modules

The method for reconstructing the cascade curve by the Cherenkov radiation in water of the NEVOD detector with a dense spatial array of optical modules is discussed. Cascades are generated by near-horizontal muons which are separated by the DECOR coordinate detector. The cascade curves and the cascade energy spectrum measured in an ～8000-hour measurement series are presented.     

Electromagnetic cascade showers with the LPM effect in standard rock initiated by extremely high-energy (1015 eV to 1021 eV) gamma-rays

Summary High-energy neutrinos produce finally high-energy electromagnetic cascade showers. For the detectio of high-energy neutrinos, it is necessary to examine the behaviour of the electromagnetic cascade showers in the higher-energy region. It is well known that the LPM effect plays a decisive role in the electromagnetic cascade shower development at higher energies. In the present paper, the behaviour of electromagnetic cascade showers including the LPM effect (LPM showers) in standard rock is examined using the calculational technique developed by Fujimaki and Misaki. In order to clarify the characteristics of LPM showers, similar calculations are also carried out for cascade showers in the absence of the LPM effect (BH showers). Comparisons between the two different kinds of cascade showers are made over electron transition curves, track lengths and fractional dissipated energies. Finally, the strong deviation of LPM showers from the normal BH showers is emphasized.     

A proposed NEVOD-EAS installation for the detection of extensive air showers

A new installation is dedicated to the independent evaluation of extensive air shower (EAS) energies detected in the NEVOD-DECOR experiment in the knee region of the energy spectrum. The design for the measuring system of the shower installation is based on clusters of scintillation detectors that are located on the roofs of laboratory buildings at MEPhI (Moscow) and will detect the electromagnetic (for near-vertical showers) and muon (for large zenith angles) EAS components. Features of the measuring system, the system for data acquisition and processing, and the results from investigating the characteristics of a single detector are discussed, along with the algorithm for event formation by the data of separate clusters.     

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°).     

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.     

EMMA—a new underground cosmic-ray experiment

An experiment observing underground muons originating from cosmic-ray air showers is under preparation in the Pyhäsalmi mine, Finland. The aim is to cover an area of about 200–300 m², and the detector setup is capable of measuring the muon multiplicity and their lateral distribution. The detector is placed at a depth of about 85 m (corresponding about 240 m w.e.), which gives a threshold energy of muons of about 45 GeV. The detection of the multimuon events is motivated by partly unknown composition of the primary cosmic rays in the energy region of 10¹⁵–10¹⁶ eV, i.e., the knee region. In addition, by measuring only the higher energy muons of the air shower, the lowest energy muons being filtered out by the rock overburden, the data is sensitive also to the studies of the upper parts of the air shower. The experiment will be constructed mainly using drift chambers used previously in LEP detectors at CERN, but it can also be expanded using plastic scintillator detectors. The prototype detector is expected to be running in the beginning of 2006, and the full-size detector by the end of 2007.