Results 1 - 10 of 5213
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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] A systematic analysis of the A-dependence of phi-meson production in proton-nucleus collisions is presented. We apply different formalisms for the evaluation of the phi-meson distortion in nuclei and discuss the theoretical uncertainties of the data analysis. The corresponding results are compared to theoretical predictions. We also discuss the interpretation of the extracted results with respect to different observables and provide relations between frequently used definitions. The perspectives of future experiments are evaluated and estimates based on our systematical study are given.
[en] The production of Δ0(1232)-resonances in p+12C collisions at 4.2 GeV/c was investigated with 4π acceptance. The masses and widths of the resonances were obtained from ananalysis of foreground and background invariant-mass distributions of pπ - pairs obtained using an angular criterion. The fraction of charged π--mesons coming from the Δ0(1232) decay was estimated and compared to those obtained in earlier analyses. The momentum, transverse momentum, kinetic energy, rapidity, and emission angle distributions as well as the invariant cross-sections of Δ0(1232)-resonances were constructed in the laboratory frame. The freeze-out temperature of the Δ0(1232)-resonances produced in p+12C collisions was estimated and compared to the freeze-out temperatures obtained using different methods for Δ(1232)-resonances produced in other experiments with different sets of colliding nuclei at various incident energies. (orig.)
[en] The stellar 14O (α, p) 17F reaction is thought to be one of the most important breakout reactions from the Hot CNO cycles into the rp-process in Type I X-ray bursters. In the present work, the properties of proton resonances in 18Ne have been investigated efficiently by utilizing a technique of proton resonant elastic scattering with a 17F radioactive-ion (RI) beam and a thick proton target. A 4.22 MeV/nucleon 17F RI beam, which was produced via a projectile-fragmentation reaction and experiencing a series of energy degradation, was separated by a Radioactive Ion Beam Line in Lanzhou (RIBLL) and bombarded a (CH2)n target. Energy spectra of the recoiled protons were measured by two sets of ΔE-E silicon telescope at center-of-mass scattering angles of θ c.m. ∼ 175 ± 5 , θ c.m. ∼ 152 ± 8 , respectively. Several proton resonances in 18Ne were observed, and their resonant parameters have been determined by an R-matrix analysis of the differential cross-sections. A doublet structure around 7.10 MeV has been identified and thought to be one state at 7.05 MeV (2+) and another one at 7.12 MeV (4+). The presently calculated total reaction rates of 14O (α, p) 17F are, at least, a factor of 1.2 ∝ 1.9 larger than the previous ones in a temperature region of 1.7 ∝ 3.0 GK mainly owing to the contribution from the 7.05 MeV (2+) state. This result implies that this breakout reaction may play a more important role than previously expected. (orig.)
[en] Differential cross-sections of the reaction p(d, 3He)γ have been measured at deuteron laboratory energies of 110, 133 and 180 MeV. The data were obtained with a coincidence setup measuring both the outgoing 3He and the photon. The data are compared with modern calculations including all possible meson-exchange currents and two- and three-nucleon forces in the potential. The data clearly show a preference for one of the models, although the shape of the angular distribution cannot be reproduced by any of the presented models. (orig.)
[en] A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuteron in the 4-momentum transfer range 0-7 fm. This procedure is made possible with the advent of recent polarization measurements. The parameterizations allow a phenomenological characterization of the deuteron electromagnetic structure. They can be used to remove ambiguities in the form factors extraction from future polarization data
[en] The β-decay of 102Sn was studied by using high-resolution germanium detectors as well as a Total Absorption Spectrometer (TAS). A decay scheme has been constructed based on the γ-γ coincidence data. The total experimental Gamow-Teller strength BGTexp of 102Sn was deduced from the TAS data to be 4.2(9). A search for β-delayed γ-rays of 100Sn decay remained unsuccessful. However, a Gamow-Teller hindrance factor h = 2.2(3), and a cross-section of about 3nb for the production of 100Sn in fusion-evaporation reaction between 58Ni beam and 50Cr target have been estimated from the data on heavier tin isotopes. The estimated hindrance factor is similar to the values derived for lower shell nuclei