Search

Abstract The MEG II experiment, based at the Paul Scherrer Institut in Switzerland, reports the result of a search for the decay $$\upmu ^+ \rightarrow {\textrm{e}}^+ \upgamma $$ μ + → e + γ from data taken in the first physics run in 2021. No excess of events over the expected background is observed, yielding an upper limit on the branching ratio of $${\mathcal {B}} (\upmu ^+ \rightarrow {\textrm{e}}^+ \upgamma ) < 7.5 \times 10^{-13}$$ B ( μ + → e + γ ) < 7.5 × 10 - 13 (90% CL). The combination of this result and the limit obtained by MEG gives $${\mathcal {B}} (\upmu ^+ \rightarrow {\textrm{e}}^+ \upgamma ) < 3.1 \times 10^{-13}$$ B ( μ + → e + γ ) < 3.1 × 10 - 13 (90% CL), which is the most stringent limit to date. A ten-fold larger sample of data is being collected during the years 2022–2023, and data-taking will continue in the coming years.

Abstract We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X, $$\upmu ^+ \rightarrow \mathrm {e}^+\mathrm {X}, \mathrm {X} \rightarrow \upgamma \upgamma \ $$ μ + → e + X , X → γ γ . This search uses a dataset resulting from $$7.5\times 10^{14}$$ 7.5 × 10 14 stopped muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013. No significant excess is found in the mass region 20–45 MeV/c $$^2$$ 2 for lifetimes below 40 ps, and we set the most stringent branching ratio upper limits in the mass region of 20–40 MeV/c $$^2$$ 2 , down to $${\mathcal {O}}(10^{-11})$$ O ( 10 - 11 ) at 90% confidence level.

We present a simple and affordable method for making a surface electrodynamic trap for microparticles. The principles of electrodynamic trapping of charged particles are discussed and step-by-step instructions on how to make a surface trap are given. In addition to the electrodynamic trap implementation and operation process, options for its further use are proposed. The work may be of interest to physics teachers as a material for practical work, for the formation of students' skills in performing a physical experiment.

The aim of the work was to study the genetic diversity and spatial-temporal genotype structure of Yersinia pestis subspecies central asiatica biovar altaica in the Gorno-Altai natural plague focus, using MLVA25-typing.Materials and methods. MLVA25-typing of 330 strains of Y. pestis ssp. central asiatica bv. altaica, isolated in the Gorno-Altai mountain natural plague focus during 1961–2015 was carried out. The phylogenetic tree was constructed with the help of UPGMA and MST algorithms.Results and discussion. The analyzed strains have been differentiated into 34 MLVA types based on cluster analysis. The formed major groups of strains show pronounced spatial confinedness. Three chorological groupings of the plague agent with peculiar genotype characteristics have been identified. Each of the groupings is circulating among the main carrier (Ochotona pallasi) population and within the limits of the similarly-named mesofocus, respectively (Ulandryksky, Tarkhatynsky and Kuraisky). MLVA25 structure of Y. pestis in Ulandryksky and Kuraisky mezofoci show stability over time; there are no significant changes from the time of their first detection in 1961 and 1999, respectively. The dramatic changes in MLVA25 structure are observed in Tarkhatynsky mesofocus, which is known from 1972. Mass expanding of the MLVA25 types which were very rare before took place there from the beginning of 1990-s, along with elimination of the types absolutely dominant up to 1980s. Most likely the changing of dominating genotypes is attributable to the bottleneck effect, arising from the sharp decline of the focal epizootic activity in the mid 1980s.

The aim of the work – analysis of peculiarities of the plague epizooty found in the southern steppe part of the Ukok Plateau in 2020.Materials and methods. Epizootiological survey was conducted over the area of 1573 km2 in July and August, 2020. 141 mammals, 157 ectoparasites (including 152 fleas), 17 bone remains samples, and 50 regurgitates of predatory birds have been tested for plague.Results and discussion. The background species of mammals – natural hosts of Yersinia pestis in the southern steppe part of the Ukok plateau are gray marmot, long-tailed souslik, and Daurian pika. Abundance of the gray marmot was high and amounted to 1.7±0.18 inhabited burrows per 1 ha (n=30) with 90 % occupancy. Three strains of Yersinia pestis ssp. pestis have been isolated: from Oropsylla alaskensis fleas collected from long-tailed souslik, gray marmot carcass, and regurgitates of predatory birds. Yersinia pestis DNA have been detected in 14 objects. Eight positive results of serological tests have been obtained. The epizooty area that was confirmed by Yersinia pestis isolation totaled 252 km2 . As a result of the survey the circulation of Yersinia pestis ssp. pestis have been for the first time established on the Ukok Plateau. The target species – the gray marmot, as well as the long-tailed souslik, are actively involved into the epizooty.

The review presents the materials on the use of mobile laboratories, developed in the Russian Federation, in the framework of four main areas: monitoring of territories to identify the circulation of pathogens of natural-focal infectious diseases; monitoring of territories during the exacerbation of the epizootic situation; participation in the elimination of outbreaks of infectious diseases; monitoring of territories to control and predict the epidemiological and epizootiologic situation in preparation for mass events. The tactical and technical characteristics and the procedure for organizing the operation of the mobile laboratory for monitoring and diagnostics mounted on the platform of the KamAZ chassis are considered. A distinctive feature of the laboratory from the existing Russian and foreign counterparts is the availability of the necessary conditions for conducting research using bacteriological analysis, rapid and accelerated diagnostic methods, and performing a full cycle of works – from the preparatory stage to the destruction of infected material. Hightech equipment allows the realization of two research schemes: the first – bacteriological analysis alongside the PCR, which ensures high reliability of the results; the second – conducting the PCR at the first stage, and when identifying genetic markers of the pathogen – performing bacteriological analysis of positive samples in order to isolate the culture of the pathogen and identify it subsequently. The second scheme will reduce the volume of bacteriological studies; make changes in the tactics of epizootiological survey. Tests of the mobile laboratory have demonstrated the effectiveness of its use in the epizootiological examination of natural plague foci, including cross-border ones. Owing to the use of a mobile laboratory in the Gorno-Altaisk high-mountain natural focus of plague, a new epizootic site was identified, located in a remote area, used by the population as a summer pasture for grazing domestic animals. The use of mobile laboratories will strengthen the laboratory base of institutions that monitor particularly dangerous, natural-focal and other dangerous infectious diseases; will help to bring the advanced diagnostic technologies directly to the natural focus, reduce the risk of epidemic complications due to plague and other particularly dangerous infections in cross-border natural foci.

The aim of the study was molecular-genetic identification and analysis of the phylogenetic relationship of Yersinia pestis strains isolated on the Ukok Plateau in 2020, in order to establish the current boundaries of the natural mega focus of plague in the Altai Mountains in Russia and Mongolia.Materials and methods. 37 strains of Y. pestis of the main subspecies isolated in the Tuva mountain and Gorno-Altai high-mountain plague foci and adjacent territories of Mongolia in 1971–2020 were studied. The whole genome sequencing of the strains was performed using the Ion S5 XL System (Thermo Fischer Scientific). Ion Torrent Suite software package 5.12 and Newbler gsAssembler 2.6 were used to process the data and assemble de novo the sequences of raw reads. The average size of the collected genome was 4.55 million base pairs. Core SNPs were detected by aligning the contigs of Y. pestis strains on the CO92 genome using the Snippy 4.6 program, then 28 SNP homoplasies were removed. The resulting set of SNPs contained only the core region of the genome (955 SNPs). The dendrogram was constructed using the Maximum Likelihood method applying the PhyML 3.1 program.Results and discussion. The current population structure of Y. pestis of the main subspecies, antique biovar, phylogenetic line 4.ANT, endemic to the foci of the Altai Mountains in Russia and Mongolia has been determined. The presence of 4.ANT-21 clone, which became widespread in the territory of these natural foci of plague at the begining of the XXI century, was revealed. It is shown that three strains isolated on the Ukok Plateau in 2020 belong to clone 4.ANT-21. According to phylogenetic analysis, evidence of 4.ANT circulation on the Ukok Plateau before 2018 was obtained. The lesson that has been learned is that it is necessary to study the territories of Mongolia, Kazakhstan and China bordering the Ukok Plateau in order to establish the current boundaries of the 4.ANT mega focus.