Skobeltsyn Institute of Nuclear Physics
Lomonosov Moscow State University

Laboratory of the theory of photon cascades

The Laboratory of the theory of photon cascades (LTPC) leaded by Sc.D. Tatiana Roganova was organized in 1971.

The basic directions of scientific research of the Laboratory scientists are within the frames of the scientific field "Theoretical and experimental studies of radiation transfer in the terrestrial and astrophysical environment". They are:

- participation in the development and realization of international experiment OPERA intended on the observations of neutrino oscillations from muon type into tau one in the neutrino beam generated by CERN accelerator (Switzerland). This beam covers about 730 km in the Earth's crust from CERN to Gran Sasso laboratory (Italy) where tau-leptons are supposed to be detected directly in nuclear emuslion contained in the detector. The scientists of the Laboratory are involved directly in the processing of nuclear emulsions by means of standardized program of the experiment using SINP scanning complex;

- analysis of the primary cosmic rays basing of the data of the stratospheric experiment RUNJOB intended on the studies of nuclear composition of primary cosmic rays;

- simulation of evaluation of giant air showers energy basing on the signals from the ground-based and underground scintillation detectors of Yakutsk experimental complex. Signal values are compared with the values of primary particles' energy of muclti-level numeric air shower computation scheme within the frames of standard model of hadron interactions. Possible sources of cosmic rays of super-high energy are studied;

- development of astrophysical complex SHPERE in order to study cosmic rays of super-high and ultra-high energy (10¹⁶ - 10¹⁸ eV). Unique methode laid in the basis of the SPHERE experiment is developed from the idea of the Soviet Academician Alexander Chudakov and it is used for the first time. At night a small experimental instrument is lifted up by means of aerostate above the Earth's surface covered with snow in order to detect Cherenkov radiation (Cherenkov light) produced by Auger showers and reflected from the snow surface. In active experimental plant SPHERE-2 the image of CHerenkov light spot and shower track are projected to the mosaic of 109 photomultiplyers by means of spheric mirror 1.5 m in diameter. This method allows to analyse structure of energy spectrum, nuclear compostion ob primary osmic rays and provides larger effective square of registration. SPHERE-2 provides better refinement of the measured spatial-temporal structure of Cherenkov light flash produced by Auger showers in comaprison with other experimental instruments;

- simulation of cascades produced by high-energy gammas in the matter of active galactic nucleus and studies of the origin of specific resonance characters in the gamma-spectra within the range of 1 MeV - 1 GeV;

- analysis of particles anisotropy and alignment in the families of cosmic rays, studies of the value of transverse impulses (p_t), search for mechanisms of nuclear interactions which explain an effect of coplanar projection of particles and abnormally big p_t for superhigh energy.

The basic results obtained by the scientists of LTPC are the following:

- analysis of new phenomena in the region of fragmentation at the energy of 10¹⁴ - 10¹⁷ eV. A unique stratospheric high-energy (>10¹⁶ eV) family "STRANA" registered during emulsion experiment onboard stratospheric balloon was studied within the frames of the studies of coplanar projection of secondary particles during hadron-nuclear interactons of the cosmic rays. An effect of alignemt of the most energetic hadrons found in this interaction provides an important evidence of coplanar projection of particles existance and correctness of determination of energy ranges where this effect appears. An altitude of interaction above the experimental plant is evaluated and ususually big transeverse impulses of secondary particles (average p_t > 2.5 GeV/s) are found;

- studies of abnormal absorption of cosmic rays particles in the lead conducted with emulsion cameras in Pamir have shown that some anomalies of cascades produced by single hadrons can be explained by methodical effects. But it is still impossible to explain very slow absorption of the channels of Auger showers at high energy in calorimeter. In general the problem is needed to be studied in more details;

- studies of superhigh energy (significantly higher than Greizen-Zatsepin-Kuzmin threshold ~5*10¹⁹ eV) Auger showers is continued. An idea of Coleman and Glashow about possible infraction of Lorenz invariant character was tested by means of experimental data. Within the frames of this hypothesis pions do not decay at high energy and it results in a more fast evolution of the shower, decreasing of the maximum depth and increasing of muon generation altitude. It is shown, that in case Lorenz invariant character infraction neutral and charged pions can be produced in primary cosmic rays at superhigh energy. The upper estimate of gammas' portion (~36%) in the primary cosmic rays at the energy of ≥ 10²⁰ eV and it essentially limits the models with topological defects and superhigh particles;

- a function A exp (-(x-c)2/(a(x-c)+2b2) is proposed. It allows to approximate wide variety of distributions appeared during cascades evolution and to describe fluctuation processes taking into account asymmetry; the questions of application of approximation methods taking into consideration the quality of input data;

- characteristics of radio emission of cascades in different media are studied. Statistic simulation of the icnlined showers of super-high energy propagating in the atmosphere allowed to calculate spatial-angular distributions of electrons and positrons which are necessary for testing of different models of Auger shower radio-emission. In order to solve the problem of radio-emission generated by particles' cascades in the lunar soil and its venting to vacuum difference schemes for boundary problem solution for the цave equation in 2 and 3 dimensions;

- a cascade theory for high energy electromagnetic cascades' evolution in different media was developed;

- a prolonged international experiment "Pamir" on the studies of hadron-nuclear interactions of high-energy particles by means of X-ray-emulsion chambers in the mountains was carried out. One of its most important results concerns the discovery and analysis of a new phenomenon - coplanar particles' projection of the particles (alignment) in hadron-nuclear interactions of cosmic rays at super-high energy ( > 10¹⁶ eV). Itwas also found that this effect is accompanied by unusually high values of transverse impulses of secondary particles;

- an international stratospheric experiment RUNJOB aimed at the studies of the nuclear composition of primary cosmic rays was carried out;

- new estimations for the energy of Auger showers are obtained basing on the signals in scintillation detectors. They allowed to adjust
Auger showers' intensity in the region of super-high energy observed by theexperimental complexes HiRes and Yakutsk.