Concerning the scattering of K+ - mesons on nuclei, the explicit discrepancy between experimental data and optical model calculations is a longstanding problem and none of the conventional medium ...effect corrections improves significantly the agreement with the data. In this paper the cross sections for the reactions K++12C at incident momenta of the kaon Plab < 800 MeV/c are calculated on the basis of Glauber's high-energy approximation. The noneikonal corrections, Fermi motion effect and both Pauli and dynamic short-range correlations were incorporated in the Glauber approach for nuclear collisions. The influence of all these corrections on the calculation of the cross sections for the interactions of kaon with nucleus is discussed. The full calculations is compared to available data. The corrections seem to fail in reproducing the experimental data. Our results is compared to optical model calculations. We show that both our model and optical model fails to give a satisfactory description of K+-nuclei cross sections. Different attempts to remove this discrepancy with the in-medium effects taken into account are discussed.
Neutrinoless double-electron capture Blaum, K.; Eliseev, S.; Danevich, F. A. ...
Reviews of modern physics,
12/2020, Letnik:
92, Številka:
4
Journal Article
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Double-beta processes play a key role in the exploration of neutrino and weak interaction properties, and in the searches for effects beyond the standard model. During the last half century many ...attempts were undertaken to search for double-beta decay with emission of two electrons, especially for its neutrinoless mode 0 ν 2 β − , the latter having still not been observed. Double-electron capture (2EC) was not yet in focus because of its in general lower transition probability. However, the rate of neutrinoless double-electron capture 0 ν 2 EC can experience a resonance enhancement by many orders of magnitude when the initial and final states are energetically degenerate. In the resonant case, the sensitivity of the 0 ν 2 EC process can approach the sensitivity of the 0 ν 2 β − decay in the search for the Majorana mass of neutrinos, right-handed currents, and other new physics. An overview of the main experimental and theoretical results obtained during the last decade in this field is presented. The experimental part outlines search results of 2EC processes and measurements of the decay energies for possible resonant 0 ν 2 EC transitions. An unprecedented precision in the determination of decay energies with Penning traps has allowed one to refine the values of the degeneracy parameter for all previously known near-resonant decays and has reduced the rather large uncertainties in the estimate of the 0 ν 2 EC half-lives. The theoretical part contains an updated analysis of the electron shell effects and an overview of the nuclear-structure models, in which the nuclear matrix elements of the 0 ν 2 EC decays are calculated. One can conclude that the decay probability of 0 ν 2 EC can experience a significant enhancement in several nuclides.
We report on the experimental evidence for a nanosecond timescale spin memory based on nonradiative excitons with large in-plane wave vector. The effect manifests itself in magnetic-field-induced ...oscillations of the energy of the optically active (radiative) excitons. The oscillations detected by a spectrally resolved pump-probe technique applied to a GaAs/AlGaAs quantum well structure in a transverse magnetic field persist over a timescale, which is orders of magnitude longer than the characteristic decoherence time in the system. The effect is attributed to the spin-dependent electron-electron exchange interaction of the optically active and inactive excitons. The spin relaxation time of the electrons belonging to nonradiative excitons appears to be much longer than the hole spin relaxation time.
A technology for evaluating the dynamic properties of mechanical vibration systems within the framework of structural and mathematical modeling methods with the use of dynamic characteristics of the ...structure of vibration fields of technological machines has been developed. We consider the problem of developing a mathematical model that allows us to correct the dynamic state depending on the system parameters based on local estimates of the properties of the vibration field. The ratio of reactions is used to evaluate the dynamic state of the vibration field. The coupling coefficient of external harmonic perturbations and the mass-inertia characteristic of a device for converting motion are considered as parameters of a mechanical oscillatory system. Based on a model with two degrees of freedom and two external influences, a detailed method for constructing mathematical models for evaluating local features of the vibration fields of technological machines is proposed. The obtained analytical expressions allow us to construct diagrams of the characteristics of mechanical oscillating systems depending on the parameters of the adjustment tools.
Quantum-mechanical shell effects are expected to strongly enhance nuclear binding on an "island of stability" of superheavy elements. The predicted center at proton number Z = 114, 120, or 126 and ...neutron number N = 184 has been substantiated by the recent synthesis of new elements up to Z = 118. However, the location of the center and the extension of the island of stability remain vague. High-precision mass spectrometry allows the direct measurement of nuclear binding energies and thus the determination of the strength of shell effects. Here, we present such measurements for nobelium and lawrencium isotopes, which also pin down the deformed shell gap at N = 152.
In Penning traps electromagnetic forces are used to confine charged particles under well-controlled conditions for virtually unlimited time. Sensitive detection methods have been developed to allow ...observation of single stored ions. Various cooling methods can be employed to reduce the energy of the trapped particle to nearly at rest. In this review we summarize how highly charged ions (HCIs) offer unique possibilities for precision measurements in Penning traps. Precision atomic and nuclear masses as well as magnetic moments of bound electrons allow among others to determine fundamental constants like the mass of the electron or to perform stringent tests of fundamental interactions like bound-state quantum electrodynamics. Recent results and future perspectives in high-precision Penning-trap spectroscopy with HCIs will be discussed.
A novel approach based on the projection of the Penning-trap ion motion onto a position-sensitive detector opens the door to very accurate mass measurements on the ppb level even for short-lived ...nuclides with half-lives well below a second. In addition to the accuracy boost, the new method provides a superior resolving power by which low-lying isomeric states with excitation energy on the 10-keV level can be easily separated from the ground state. A measurement of the mass difference of ^{130}Xe and ^{129}Xe has demonstrated the great potential of the new approach.
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