Results 1 - 10 of 5473
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[en] The doubly magic N = Z nucleus 56Ni has been investigated with two fusion-evaporation reactions; 40Ca(28Si, 3a)56Ni at a beam energy of 122MeV and 28Si(32S, 2p2n)56Ni at 130MeV. To detect γ-rays in coincidence with evaporated particles the Ge-detector array Gammasphere was used in conjunction with the charged-particle detector system, Microball and a 1p neutron detector array. Results include a significantly extended level scheme of 56Ni, which is compared to large-scale shell model calculations in the fp shell. The experimental and theoretical results agree to a large extent, with one notable exception; the theoretical model fails to predict the proper sequence of the yrast and yrare 8+ states
[en] A covariant quark model, based both on the spectator formalism and on Vector Meson Dominance, and previously calibrated by the physical data, is here extended to the unphysical region of the lattice data by means of one single extra adjustable parameter - the constituent quark mass in the chiral limit. We calculated the Nucleon (N) and the Gamma N -> Delta form factors in the universe of values for that parameter described by quenched lattice QCD. A qualitative description of the Nucleon and Gamma N -> Delta form factors lattice data is achieved for light pion masses.
[en] The e p→ eprime p ρ0 reaction has been measured, using the 5.754 GeV electron beam of Jefferson Lab and the CLAS detector. This represents the largest ever set of data for this reaction in the valence region. Integrated and differential cross sections are presented. The W$, Q2 and t$ dependences of the cross section are compared to theoretical calculations based on t$-channel meson-exchange Regge theory on the one hand and on quark handbag diagrams related to Generalized Parton Distributions (GPDs) on the other hand. The Regge approach can describe at the ∼ 30% level most of the features of the present data while the two GPD calculations that are presented in this article which succesfully reproduce the high energy data strongly underestimate the present data. The question is then raised whether this discrepancy originates from an incomplete or inexact way of modelling the GPDs or the associated hard scattering amplitude or whether the GPD formalism is simply in
[en] The energy spectra of light-mass kaonic nuclei were investigated using the theoretical framework of the 0s-orbital model with zero-range and interactions of effective single-channel real potentials. The energies of the , , , , and systems were calculated in the cases of weak- and deep-binding of the interaction, which was adjusted to fit the Λ(1405) mass with the energy of the bound state. The results qualitatively reproduced the energy systematics of the ground states of kaonic nuclei calculated via other theoretical approaches. In our simplified model, the lowest states (J, T = 0,1/2) and (0,0) were found to have binding energies approximately twice and four times as large as that of the (1/2, 0) state, respectively. Higher (J, T) states including (1, 1/2), (0,1), and (1,1) were predicted at energies of 9-25 MeV below the antikaon-decay threshold. The effective Λ(1405)-Λ(1405) interaction in the system was also investigated via a +-cluster model. Strong and weak The Λ(1405)-Λ(1405) attractions were obtained in the S = 0 and S = 1 channels, respectively. The Λ(1405)-Λ(1405) interaction in the system was compared with the effective d-d interaction in the NNNN system, and the properties of dimer-dimer interactions in hadron and nuclear systems were discussed.
[en] In this work, we study magnetic field effects on neutron star matter containing the baryon octet and additional heavier spin 3/2 baryons (the Δ's). We make use of two different relativistic hadronic models that contain an additional vector-isovector self interaction for the mesons: one version of a relativistic mean field (RMF) model and the chiral mean field (CMF) model. We find that both the additional interaction and a strong magnetic field enhance the Δ baryon population in dense matter, while decreasing the relative density of hyperons. At the same time that the vector-isovector meson interaction modifies neutron-star masses very little (< 0.1 M), it decreases their radii considerably, allowing both models to be in better agreement with observations. Together, these features indicate that magnetic neutron stars are likely to contain Δ baryons in their interior.
[en] The mass spectrum of hidden charm pentaquark states composed of two diquarks and an antiquark are calculated by use of an effective Hamiltonian which includes explicitly the spin, color, and flavor dependent interactions. The results show that the P(4312) and P(4440) states could be explained as hidden charm pentaquark states with isospin and spin-parity IJ = 1/2 (3/2), the P(4457) state could be explained as a hidden charm pentaquark state with IJ = 1/2 (5/2), and the P(4459) state could be explained as a hidden charm pentaquark state with IJ = 0 (1/2) or 0 (3/2). Predications for the masses of other possible pentaquark states are also given, and the possible decay channels of these hidden charm pentaquark states are discussed.
[en] Lifetimes of states in the negative-parity band, based on the ν(h) orbital in Pd, have been measured in the spin range from 27/2 to 39/2 using the Doppler-Shift Attenuation Method. The inferred B(E2) values are observed to decrease with increasing angular momentum and J/B(E2) values are found to be large (> 300 MeV(eb)). These observations along with calculations based on the semiclassical particle-rotor model approach suggest that antimagnetic and collective rotation, along with gradual neutron alignment are responsible for angular momentum generation in the band under consideration.
[en] In recent years there has been much progress on the investigation of the QCD phase diagram with lattice QCD simulations. In this review we focus on the developments in the last two years. Especially the addition of external influences or new parameter ranges yields an increasing number of interesting results. We discuss the progress for small, finite densities from both extrapolation-based methods (Taylor expansion and analytic continuation for imaginary chemical potential) and complex Langevin simulations, for heavy quark bound states (quarkonium), the dependence on the quark masses (Columbia plot) and the influence of a magnetic field. Many of these conditions are relevant for the understanding of both the QCD transition in the early universe and heavy ion collision experiments, which are conducted for example at the LHC and RHIC.
[en] In the present work, we have employed the theoretical framework of Triaxial Projected Shell Model (TPSM) to investigate the presence of triaxiality in transitional nuclei of Hf. We have obtained the calculated yrast and γ-bands and compared with the corresponding experimental data. In addition to these, γγ-bands are also predicted. In order to thoroughly understand the structure of yrast and γ-bands, we have kept our focus to study low energy states. The yrast energy ratios, staggering in γ-bands, the phenomenon of back-bending, the reduced electromagnetic transition probabilities and g-factors are calculated using TPSM.
[en] The fission cross section of Th has been measured at fast neutron energies, using a setup based on Micromegas detectors. The experiment was performed at the 5.5 MV Van de Graaff Tandem accelerator in the neutron beam facility of the National Centre for Scientific Research ''Demokritos''. The quasi-monoenergetic neutron beams were produced via the H(p,n), H(d,n) and H(d,n) reactions, while the U(n,f) and U(n,f) reactions were used as references, in order to acquire cross-section data points in the energy range 2-18 MeV. The characterization of the actinide samples was performed via α-spectroscopy with a Silicon Surface Barrier (SSB) detector, while Monte Carlo simulations with the FLUKA code were used to achieve the deconvolution of the Th α peak from the α background of its daughter nuclei present in the spectrum. Special attention was given to the study of the parasitic neutrons present in the experimental area, produced via charged particle reactions induced by the particle beam and from neutron scattering. Details on the data analysis and results are presented.