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Now showing items 1 - 16 of 46

  • Probing the structure of exotic nuclei by transfer reactions

    Lenske, H.   Schrieder, G.  

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  • Rearrangement in the density dependent relativistic field theory of nuclei

    Lenske, H.   Fuchs, C.  

    A fully covariant density dependent hadronic field theory is obtained by describing medium effects as a field-theoretical functional dependence of meson-nucleon vertices on the baryon field operators. Rearrangement self-energies are found in the baryon field equations from the variational derivatives of the vertices. Solutions are studied in the Hartree limit and compared to the local density approximation for relativistic Dirac-Brueckner theory. Descriptions of medium effects in terms of the baryon vector and scalar density, respectively, are discussed. Hartree calculations for nuclei between 16O and 208Pb show that rearrangement improves simultaneously the description of binding energies, root-mean-square radii and density distributions.
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  • Strangeness production in antiproton-nucleus annihilation

    Larionov, A.B.   Gaitanos, T.   Lenske, H.   Mosel, U.   Wrońska, A.   Skibiński, R.   Guaraldo, C.   Kistryn, St.   Ströher, H.  

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  • Probing isospin dynamics in halo nuclei

    Lenske, H.   Hofmann, F.   Keil, C.M.  

    Nuclear many-body theory is used to study nuclear matter and finite nuclei at extreme isospin. In-medium interactions in asymmetric nuclear matter are obtained from (Dirac-) Brueckner theory. Neutron skin formation in Ni and Sn isotopes is investigated by relativistic mean-field calculations in DDRH theory with density dependent meson-nucleon vertices. Applications to light nuclei are discussed with special emphasis on pairing and core polarization in weakly bound nuclei. Approaches accounting for continuum coupling in dripline pairing and core polarization are presented. Calculations for the halo nuclei 8B, 11Be and 19C show that shell structures are dissolving when the driplines are approached. Relativistic breakup data are well described by eikonal calculations.
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  • Reaction mechanism of heavy-ion charge-exchange scattering at intermediate energies

    Lenske, H.   Wolter, H. H.   Bohlen, H. G.  

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  • Exotic nuclear matter

    Lenske, H.   Dhar, M.   Tsoneva, N.   Wilhelm, J.   Andreev, A.   Arsenyev, N.   Ershov, S.   Sargsyan, V.   Vdovin, A.  

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  • Nuclear matter spectral functions by transport theory

    Lehr, J.   Lenske, H.   Leupold, S.   Mosel, U.  

    Quantum transport theory is used to calculate the nucleon spectral function in infinite nuclear matter. A self-consistent description is obtained by utilizing the relations between collision rates and correlation functions. Static and dynamical self-energies are taken into account in the single-particle propagators. The real parts of the nonstatic self-energy contributions are calculated by dispersion theory thus conserving the analyticity of momentum distributions. The transport theoretical spectral functions, momentum distributions, occupation probabilities and response functions are in close agreement with results of variational and other many-body theoretical calculations. The results indicate that the nucleon spectral functions are determined only by the average short-range correlation strength
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  • Exploring the N alpha+3n light nuclei via the ((7)Li, (7)Be) reaction

    Nociforo, C.   Cappuzzello, F.   Cunsolo, A.   Foti, A.   Orrigo, S. E. A.   Winfield, J. S.   Cavallaro, M.   Fortier, S.   Beaumel, D.   Lenske, H.  

    Experimental signatures of the dynamical correlations of a core with a single-particle neutron have been found in light neutron-rich nuclei investigated via the ((7)Li,(7)Be) charge-exchange reactions at around 8 MeV/u. Of particular astrophysical relevance are low-lying narrow resonances (Gamma similar to 200 keV FWHM) BSEC (Bound States Embedded in the Continuum). Because of their long lifetime BSEC states are likely to effect the capture rates in any scenario for nucleosynthesis in neutron-rich environment. They have been observed in the continuum of (11)Be and (15)C nuclei. A microscopic nuclear structure model based on QRPA theory, which takes into account Dynamical Core Polarisation (DCP) correlations, gives a suitable description of these resonances as well as single-particle states of the studied systems. In this context, high-energy narrow structures populated in nuclei having an integer number of alpha-particles plus three neutrons are good BSEC candidates and can be systematically investigated.
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  • Exploring light neutron rich nuclei via the ( 7Li, 7Be) reaction

    Cavallaro, M.   Cappuzzello, F.   Cunsolo, A.   Foti, A.   Orrigo, S.E.A.   Rodrigues, M.R.D.   Borello-Lewin, T.   Lenske, H.   Petrascu, H.   Winfield, J.S.  

    A systematic study of the nuclei that can be described as an integer number of alpha particles plus three neutrons via the ( 7Li, 7Be) reaction at about 8 MeV/u has shown the presence of Bound States Embedded in the Continuum in the energy spectra. These are experimental signatures of the dynamical correlations of an easily polarizable core with a single-particle state of the valence neutron.
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  • Low-energy dipole excitations in nuclei at the N=50, 82 and Z=50 shell closures as signatures for a neutron skin

    Tsoneva, N.   Lenske, H.  

    Low-energy dipole excitations have been investigated theoretically in N = 50 (88)Sr and (90)Zr, several N = 82 isotones and the Z = 50 Sn isotopes. For this purpose a method incorporating both HFB and multi-phonon QPM theory is applied. A concentration of one-phonon dipole strength located below the neutron emission threshold has been calculated in these nuclei. The analysis of the corresponding neutron and proton dipole transition densities allows us to assign a genuine pattern to the low-energy excitations and make them distinct from the conventional GDR modes. Analyzing also the QRPA wave functions of the states we can identify these excitations as pygmy dipole resonance (PDR) modes, recently studied also in Sn and N = 82 nuclei. The results for N = 50 are exploratory for an experimental project designed for the bremsstrahlung facility at the ELBE accelerator.
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  • Giessen coupled-channel model for pion- and photon-induced reactions

    Shklyar, V.   Lenske, H.   Mosel, U.  

    The reactions (gamma/pi) -> gamma N, pi N, 2 pi N, eta N, K Lambda, K Sigma, omega N are simultaneously analysed within a coupled-channel unitary Lagrangian approach (Giessen Model). The resonance contributions to the different transition channels are shown and discussed. The results for eta N and K Lambda final states in both pion- and photo-induced reactions are presented in more details in prospect of new experimental data from MAMI and CLAS. The recent progress in the description of the 2 pi N channel in terms of the pi N -> rho N, sigma N, pi Delta transitions is presented.
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  • Formation of double-Lambda hypemuclei at PANDA

    Gaitanos, T.   Larionov, A. B.   Lenske, H.   Mosel, U.  

    We study the formation of single- and double-Lambda hypernuclei in antiproton-induced reactions relevant for the forthcoming PANDA experiment at FAIR. We use the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) transport model with relativistic mean-fields for the description of non-equilibrium dynamics and the statistical multifragmentation model (SMM) for fragment formation. This combined approach describes the dynamical properties of strangeness and fragments in low energy (p) over bar -induced reactions fairly well. We then focus on the formation of double-Lambda hypernuclei in high energy (p) over bar -nucleus collisions on a primary target including the complementary Xi-induced reactions to a secondary one, as proposed by the PANDA Collaboration. Our results show that a copious production of double-Lambda hyperfragments is possible at PANDA. In particular, we provide first theoretical estimations on the double-Lambda production cross section, which strongly rises with decreasing energy of the secondary Xi-beam. (C) 2012 Elsevier B.V. All rights reserved.
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  • The NUMEN Project @ LNS: Status and Perspectives

    Cappuzzello, F.   Agodi, C.   Acosta, L.   Auerbach, N.   Bellone, J.   Bijker, R.   Bonanno, D.   Bongiovanni, D.   Borello-Lewin, T.   Boztosun, I.   Branchina, V.   Bussa, M. P.   Calabrese, S.   Calabretta, L.   Calanna, A.   Carbone, D.   Cavallaro, M.   Calvo, D.   Lomeli, E. R. Chavez   Coban, A.   Colonna, M.   D'Agostino, G.   Degeronimo, G.   Delaunay, F.   Deshmukh, N.   de Faria, P. N.   Ferraresi, C.   Ferreira, J. L.   Fisichella, M.   Foti, A.   Finocchiaro, P.   Gallo, G.   Garcia, U.   Giraudo, G.   Greco, V.   Hacisalihoglu, A.   Kotila, J.   Iazzi, F.   Introzzi, R.   Lanzalone, G.   Lavagno, A.   La Via, F.   Lay, J. A.   Lenske, H.   Linares, R.   Litrico, G.   Longhitano, F.   Lo Presti, D.   Lubian, J.   Medina, N.   Mendes, D. R.   Muoio, A.   Oliveira, J. R. B.   Pakou, A.   Pandola, L.   Petrascu, H.   Pinna, F.   Reito, S.   Rifuggiato, D.   Rodrigues, M. R. D.   Russo, A. D.   Russo, G.   Santagati, G.   Santopinto, E.   Sgouros, O.   Solakci, S. O.   Souliotis, G.   Soukeras, V.   Spatafora, A.   Torresi, D.   Tudisco, S.   Vsevolodovna, R. I. M.   Wheadon, R. J.   Yildirin, A.   Zagatto, V.  

    The NUMEN project aims at accessing experimentally driven information on Nuclear Matrix Elements (NME) involved in the half-life of the neutrinoless double beta decay (0 nu beta beta), by high-accuracy measurements of the cross sections of Heavy Ion (HI) induced Double Charge Exchange (DCE) reactions. Particular attention is given to the (O-18, Ne-18) and (Ne-20, O-20) reactions as tools for beta+beta+ and beta-beta-decays, respectively. First evidence about the possibility to get quantitative information about NME from experiments is found for both kind of reactions. In the experiments, performed at INFN Laboratory Nazionali del Sud (LNS) in Catania, the beams are accelerated by the Superconducting Cyclotron (CS) and the reaction products are detected the MAGNEX magnetic spectrometer. The measured cross sections are challengingly low, limiting the present exploration to few selected isotopes of interest in the context of typically low-yield experimental runs. A major upgrade of the LNS facility is foreseen in order to increase the experimental yield of at least two orders of magnitude, thus making feasible a systematic study of all the cases of interest. Frontiers technologies are going to be developed, to this purpose, for the accelerator and the detection systems. In parallel, advanced theoretical models will be developed in order to extract the nuclear structure information from the measured cross sections.
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  • Compton scattering off proton in the third resonance region

    Cao, Xu   Lenske, H.  

    Compton scattering off the proton in the third resonance region is analyzed for the first time, owing to the full combined analysis of pion- and photo-induced reactions in a coupled-channel effective Lagrangian model with K-matrix approximation. Two isospin I=3D 3/2resonances D-33(1700) and F-35(1930) are found to be essential in the range of 1.6-1.8 GeV. The recent beam asymmetry data of Compton scattering from the GRAAL facility are used to determine the helicity couplings of these resonances, and strong constraints are coming also from pi N and K Sigma photoproduction data. The possible spin and parity of new narrow resonances is discussed. (C) 2017 The Author(s). Published by Elsevier B.V.
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  • Investigations of Skin Nuclei in a Density Functional Approach

    Tsoneva, N.   Lenske, H.  

    A theoretical method incorporating the density functional theory and quasiparticle-phonon model is applied for systematic study of low-energy excitations of different multipolarities related to neutron or proton skins in stable and exotic nuclei. Furthermore, the unique character of the observed excitations identified with pygmy dipole or pygmy quadrupole resonances is confirmed in quasiparticle-random-phase-approximation plus multiphonon calculations. The achievements of the multiphonon approach for description of pygmy and other strengths are discussed.
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  • Strangeness production on the nucleon and on nuclei

    Lenske, H.  

    The coupled-channel Giessen Model is used to investigate meson production on the nucleon simultaneously in reactions with hadrons and the photon. The essential aspects of the model are discussed. Results for strangeness producing K Lambda reactions on the proton and eta photoproduction on the proton and the neutron, respectively, are presented. A resonance model is used to explore the production of hypernuclei in proton and photon induced reactions. (c) 2008 Elsevier B.V. All rights reserved.
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