T. Roganova

New method for determining energies of cosmic-ray nuclei

A new procedure for determining the energies of particles of primary cosmic radiation is described. The procedure is based on measuring the spatial density of the flux of secondary particles originating from the first event of nuclear interaction that have traversed a thin-converter layer. The use of the proposed method makes it possible to create equipment of comparatively small mass and high sensitivity. The procedure can be applied in balloon-and satellite-borne cosmic-ray experiments with cosmic nuclei for all types of nuclei over a wide energy range between 1011 and 1016 eV per particle. Physical foundations of the method, results of a simulation, and the applicability range are described.

An Instrument to Measure Elemental Energy Spectra of Cosmic Ray Nuclei up to 1016 eV

Abstract A longstanding goal of cosmic-ray research is to measure the elemental energy spectra of cosmic rays up to and through the “knee” (≈3×10 15 eV). It is not currently feasible to achieve this goal with an ionisation calorimeter because the mass required to be deployed in Earth orbit is very large (at least 50 tonnes). An alternative method is presented. This is based on measuring the primary particle energy by determining the angular distribution of secondaries produced in a target layer using silicon microstrip detector technology. The proposed technique can be used over a wide range of energies (10 11 –10 16 eV) and gives an energy resolution of 60% or better. Based on this technique, a design for a new lightweight instrument with a large aperture (KLEM) is described.

Estimates of arrival directions of giant air showers

The arrival directions of giant air showers generated in the atmosphere by the primary cosmic ray particles with energies above ∼5 · 10 19 eV may be connected with possible extragalactic sources, because the Larmor radius of such particles is too large. Besides it was suggested that the primary particles with enormous energies may be neutrons. In this case it is possible to avoid the energy loss in interactions with the microwave background radiation and arrival directions will strongly point to sources. Thus it is of primary importance to decrease possible errors in the estimates of arrival directions of giant air showers. To estimate the arrival direction of a giant air shower one has to have any model of its space–time structure. The simplest model of the shower time front is a model of the flat front when all particles are located in this front plane. It was shown that possible errors in estimates of the zenith and azimuth angles which characterize the arrival directions may be as large as 5 ◦ or even more. The χ 2 method gives very large values of χ 2 . That means that this model is inconsistent with the data. A much more realistic model of a shower time front was suggested by Linsley. Calculations displayed that both the shower disk thickness and the average time delay depend on the energy of the primary particles. So the calculated time front of the shower for both electrons and muons may fit the data and thus provides better accuracy. The standard mathematical procedure to interpret data is the χ 2 method. This method leads to reasonable estimates of the zenith and azimuth angles with uncertainties of 2÷3 ◦ . In some cases the minimax procedure may be utilized to interpret data. It was shown that the possible error in estimates of the zenith and azimuth angles may be decreased up to 0.5 ◦ . At last the fuzzy uncertain variables and the possibility theory are suggested here to be used for interpreting the data. Calculations were carried out in terms of the quark-gluon string model for primary protons and an observation level of 1020 g/cm. The Landau–Pomeranchuk–Migdal effect and interactions of neutral pions with nuclei in the atmosphere at high energies are taken into account. The Monte Carlo method was used for primary protons while cascades from numerous charged pions were considered with the help of cascade equations. Though experimental statistics is very low no evidence is found to prefer any directions. Thus the isotropic distribution of the arrival directions of giant air showers with

First results obtained by RUNJOB campaign

Abstract We report experimental results obtained by using a wide-gap type emulsion chamber flown in the first Japanese-Russo joint balloon project, called RUNJOB ( RU ssia- N ippon JO int B alloon-program). Two balloons were launched from Kamchatka in July 1995, and both were recovered successfully near the Volga River. The exposure time was 130 hours for the first flight and 168 hours for the second. The mean ceiling altitude, in both flights, was 32 km corresponding to 10 g/cm 2 . Total area of the emulsion chamber was 0.8 m 2 , and the thickness 0.385 and 2.28 collision m.f.p.s for vertically incident proton- and iron-primaries, respectively. We detected 381 showers using Fuji-#200-type X-ray film; of these 174 showers were due to atmospheric secondary γ-rays, and the rest 207 came from nuclear components. The energy range covers 20∼200 TeV for proton-primary, 3∼30 TeV/nucleon for helium-primary, and 0.7∼5 TeV/nucleon for iron-primary. We give the energy spectra for various elements (proton, helium, …, iron) as well as the all-particle spectrum and the average mass of the cosmic-ray primaries.

Pions in primary cosmic rays of ultrahigh energies

In the framework of the Coleman-Glashow hypothesis of an extremely weak violation of Lorentz invariance, neutral and charged pions can be stable for energies above 1019 eV and enter into the composition of primary cosmic rays of ultrahigh energies. The kinematic exclusion of reactions of pions with relic photons is particularly important, because it allows the Greisen-Zatsepin-Kuzmin paradox to be resolved. The parameters of extensive air showers induced by primary pions calculated within the model of quark-gluon strings with allowance for the Landau-Pomeranchuk-Migdal effect and interactions of neutral pions of ultrahigh energies are not contradictory to the available data of observations. It has been shown that observations of production heights of muons with energies above 10GeV will make it possible to distinguish between primary nuclei, protons, and pions; to verify Lorentz invariance for energies above 1020 eV; and to obtain a new limit on the difference between the maximum possible velocities of muons and pions (cµ−cπ)<4×10−26.

Features of the absorption of 2-to 40-TeV cosmic-ray hadrons in lead

For the first time, experimental data on 2-to 40-TeV hadronic cascades recorded by a lead ionization calorimeter at the Tien-Shan mountain station of the Lebedev Institute of Physics (Moscow) are compared with the results of a present-day simulation based on the GEANT 3.21 code and performed with allowance for the detection procedure. The conclusion that along-flying component appears in high-energy hadronic cascades was drawn previously on the basis of these data. Some special features of the procedure for recording TeV-range hadrons in the calorimeter are considered. It is shown that the averaged hadronic cascades and various features of single cascades having energies below 10 TeV are simulated adequately by using the QGSJET + FLUKA generators of nuclear interactions, but that they are not described by using the GHEISHA generator at lower energies. Some features of the experimentally observed cascades could not be described for cascade energies above 10 TeV.

Longitudinal development of giant air showers and problem of estimating the energy of primary-cosmic-ray particles

The attenuation length for the charged-particle density at a distance of 600 m from the shower axis may differ from that adopted in experimental investigations by 40–50%. This casts some doubt on experimental estimates previously obtained for the energy of primary-cosmic-ray particles in the region of ultrahigh energies.