Determining the nature of dark matter (DM) is one of the most important challenges of modern experimental physics. This article overviews the major arguments confirming the existence of DM, gives the latest classifications of DM particles, identifies possible candidates for their role, and discusses the most significant DM particle search experiments conducted and under development. The article mainly aims to give an idea of diverse experimental methods of and approaches to registering DM particles, as well as of the currently available results of the search for them, which open new prospects in DM studies and contribute to solving topical problems in New Physics.

The method of using natural track detectors, i.e., meteorite olivine crystals, is developed and improved applied to the problem of searching for superheavy nuclei in nature, in galactic cosmic rays (GCR). The new technique implements the sequence of etching, grinding, and track identification operations using the automated PAVICOM facility. The data on the track length and etching rate in combination with the results of calibration on heavy nucleus accelerators allowed the development of a technique for determining the GCR nucleus charge with an accuracy of ±2. On this basis, a significant set of experimental data on superheavy nuclei of natural origin was obtained (21743GCRheavy nucleiwith Z >20, including three nucleiwith a charge of 119 −6 +10 ). The minimum lifetime T min of the last-mentioned is within 50 years< T min < 100 years, which exceeds the lifetime of transfermium nuclei synthesized on accelerators by many orders of magnitude. The long-lived superheavy nuclei detected in the GCR spectrum can belong to the “stability island”.

This paper focuses on the basic principles of the muon radiography method, reviews the major muon radiography experiments, and presents the first results in Russia obtained by the authors using this method based on emulsion track detectors.

An original method of studying chemically etched tracks of heavy nuclei in olivine from pallasite meteorites was used to obtain a charge distribution of approximately 9000 nuclei with charges above 55 in galactic cosmic rays. Three superheavy nuclei with the charges in the range of 105<Z<130 were detected. Regression analysis enabled to amend the charge of one of these nuclei up to the value 119(-6)(+10) with the probability of 95%. Such nuclei have to form islands of stability of superheavy elements; their occurrence in nature supports the validity of theoretical predictions and justifies efforts for their synthesis under the Earth conditions.

The charge distribution of approximately 6000 nuclei with charge numbers above 55 in galactic cosmic rays has been obtained in the OLIMPIYA project. Three superheavy nuclei with the charge numbers in the range 105 < Z < 130 have been detected. The regression analysis has provided a more accurate estimate of the charge number of one of these nuclei (119 −6 +10 with a probability of 95%). Such nuclei should form stability islands. Their detection in nature confirms theoretical predictions and justifies efforts for their synthesis under terrestrial conditions. The model calculations performed in this work possibly can explain the results of some experiments on the investigation of the charge composition of cosmic rays in which particles with charge numbers in the range 94 < Z < 100 were detected (they cannot enter into the composition of primary cosmic radiation because their lifetime is very short). The calculations indicate that events with Z > 92 are due to the fragmentation of heavier nuclei from the stability island, rather than to methodical inaccuracies or fault of instruments. Several such events have been revealed. Thus, the track method makes it possible to obtain the results very important for understanding of the physical picture of the world. The results obtained within the OLIMPIYA project show that the study of tracks of galactic cosmic rays in olivine crystals from meteorites opens new capabilities for the investigation of fluxes and spectra in cosmic rays in the region of heavy and superheavy nuclei.

The results are presented of model calculation of the interaction and yield of galactic-cosmic-ray superheavy-element nuclear fragmentation products from the 50 < Z < 92 range of their charges as they pass through a certain meteorite-pallasite substance thickness.

Time measurements in detecting particles from radioactive radiation sources are one of the main types of measurements in many branches of science and engineering: nuclear physics, space researches, nuclear medicine. The developed precise time stamp generator DWDC (Discriminator With Digital Correction) with a dead time of 25 ns is intended for applications in basic research of matter. It is planned to modernize the acquisition system of the T0 starting trigger detector using the DWDC module (ALICE experiment).

This paper presents experimental results on galactic cosmic ray nuclei in olivine crystals from the Marjalahti and Eagle Station pallasites. The charge spectrum of the nuclei is measured to be in good agreement with the experimental data from the HEAO-3 and ARIEL-6 satellite missions.

The measurement of positron--nucleus collisions was used to estimate the possibility of suppressing background events that simulate $\beta\beta$ decay in the emulsion region adjacent to molybdenum conglomerates. The range of the escape of two relativistic particles from the interaction was found to be $ = (0.60\pm 0.03) ~\mu$m, which approximately corresponds to the grain size of developed nuclear emulsion. No correlation of the values of d with the angle between two relativistic particles was observed. It was shown that it was possible to exclude $\beta\beta$ decay background from electrons emerging in the decay of elements of naturally occurring radioactive chains. The background from $\beta$ decays of $^{90}$Sr and $^{40}$K available in emulsion around Mo conglomerates was determined by the ratio of the volume $(\sim d^3)$ to the total volume of emulsion and was found to be $1.5\cdot 10^{-2}$. It was shown that the backgrounds from $^{40}$K, $^{90}$Sr and natural radioactivity could be significantly suppressed and would not limit the sensitivity of the experiment with 1 kg $^{100}$Mo.

New results of the measurements performed in the “OLIMPIA” project framework of the relative abundance of superheavy (Z≥50) nuclei in galactic cosmic rays are presented. The method of detection and analysis of nucleus tracks in olivine crystals from the Marjalahti pallasite was based on the combination of the multistage etching of individual crystals and measurement of the track parameters (etchable length and corresponding track-etching rate) on the completely automated PAVICOM setup.

To identify the charge of detected cosmic ray nuclei, it is necessary that the dynamic and geometric parameters of tracks (the etching rate of a nuclear track, as well as the length and the diameter of the track channel) be determined with a high accuracy. Results of the experimental investigations of tracks produced in olivine crystals from the Marjalahti pallasite by accelerated Xe and U nuclei are presented. These investigations were performed as part of the Olimpiya project. It is shown that the etching rate and the fully etched track length are independent of the track orientation relative to the crystallographic symmetry axes of each olivine crystal under investigation.