Results 1 - 10 of 1049
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[en] The Dyson-Schwinger approach to mesons as quark-antiquark bound states produces a very satisfactory description of the whole light pseudoscalar nonet, both at zero and at finite temperatures . Especially interesting is the temperature behavior of the η-η′ complex, where results for masses differ very greatly for various possible relationships between the chiral restoration temperature and the temperature of melting of the topological susceptibility χ. Namely, χ is connected with the quantity β in the η-η′ mass matrix as χ = β (2 +X 2)f2π/6, where . For example, in certain regimes, the “mass” of η NS , namely , for some temperatures becomes larger than , the “mass” of η S ; that is, and can can cross.
[en] The satellite borne Pamela instrument is dedicated to the precise and high statistics study of CR fluxes on a four decades energy range. Pamela experiment is the last step of the “Russian-Italian Mission” (RIM) program established in 1992 between several Italian and Russian institutes and with the participation of Sweden and Germany. Designed as a cosmic ray observatory at 1 AU, it extensive program is made possible thanks to the outstanding performance of the instrument, the low energy threshold, the quasi-polar orbit and the 10 years duration of the observation. The physics program pays particular attention to the study of particles and antiparticles fluxes and includes search for dark matter, primordial antimatter, new matter in the Universe, study of cosmic-ray propagation, solar physics and solar modulation, and terrestrial magnetosphere. Very important is the discovery of the anomalous increase of the positron flux at energies higher that 50 GeV (the so called “Pamela anomaly”), and the abrupt spectral hardening of H and He, challenging the current paradigm of cosmic-ray acceleration and propagation in the Galaxy.
[en] Direct production of heavy particles and their indirect signatures, detected at the LHC as anomalous events, are considered. Analogous anomalous events at comparable c.m.s. energies were detected in cosmic-ray experiments several decades ago. All these exotic phenomena and processes can be interpreted from a common viewpoint by assuming the production of quark-gluon blobs with large orbital momenta which hinder the emission of light rather than heavy quarks including the top quarks. The prospects for testing this model in the LHC experiments are discussed.
[en] This paper is giving an overview of recent ATLAS results on the production cross sections of gauge boson pairs decaying leptonically using data from pp collisions at √s = 13 TeV for ZZ and at √s = 8 TeV for W± Z and W± W± at the LHC at CERN. The cross sections are found to be in agreement with the expectations from the Standard Model within the estimated uncertainties. The production cross section measurements also allow for studies of anomalous triple and quartic gauge couplings for which 95% confidence level limits are set.
[en] The phenomenological analysis of J /ψ and D meson production in Pb-Pb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair is fulfilled in the framework of the two-component HYDJET++ model, which includes the thermal and nonthermal production mechanisms. A significant fraction of D -mesons is found to be in a kinetic equilibrium with the created matter, while J /ψ-mesons are characterized by earlier (as compared to light hadrons) freeze-out.
[en] The activity of the 51Cr source in the BEST experiment searching for sterile neutrinos is planned to be determined by measuring the spectrum of internal bremsstrahlung. The measurements of activity and the spectrum of internal bremsstrahlung of point low-activity 51Cr sources with Ge semiconductor detectors are discussed. The accuracy and errors of this measurement method are examined.
[en] Activities performed in preparation for the search for ternary fission of heavy nuclei and the analysis of fragment angular correlations with nuclear track emulsion and an automated microscope are detailed. Surface irradiation of nuclear emulsion by a Cf source was initiated. Planar events containing nothing but fragment triples were found and studied.
[en] In-source laser spectroscopy experiments for bismuth isotopes at the 306.77 nm atomic transition has been carried out at the IRIS (Investigation of Radioactive Isotopes at Synchrocyclotron) facility of Petersburg Nuclear Physics Institute. New data on isotope shifts for 189–198,211Bi isotopes and isomers have been obtained. The changes in the mean-square charge radii were deduced. The large isomer shift has been observed for the intruder isomer states of Bi with spin I = 1/2 (A = 193, 195, 197). This testifies to the shape coexistence in these nuclei with the intruder isomer states more deformed than the ground states. Marked deviation from the nearly spherical behavior for ground states of the even-neutron Bi isotopes at N < 109 is demonstrated, in contrast to the Pb and Tl isotopic chains.
[en] Production of the ψ(2S) and ϒ(3S) mesons is considered in the framework of the leading order parton Reggeization approach and within the NRQCD factorization hypothesis. A self-consistent description of the pT spectra at low pT (fusion model) and high pT (fragmentation model) is obtained. The fusion model predictions for polarization observables agree with experiment for ϒ(3S) and are at variance with experiment for ψ(2S).
[en] Starting from a Skyrme interaction with tensor terms, the β-decay rates of 52Ca have been studied within a microscopic model including the 2p − 2h configuration effects. We observe a redistribution of the strength of Gamow-Teller transitions due to the 2p − 2h fragmentation. Taking into account this effect results in a satisfactory description of the neutron emission probability of the β-decay in 52Ca.