E. Khan

Université Paris-Sud 11, Orsay, Île-de-France, France

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Publications (116)283.18 Total impact

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    ABSTRACT: Spin-orbit coupling characterizes quantum systems such as atoms, nuclei, hypernuclei, quarkonia, etc., and is essential for understanding their spectroscopic properties. Depending on the system, the effect of spin-orbit coupling on shell structure is large in nuclei, small in quarkonia, perturbative in atoms. In the standard non-relativistic reduction of the single-particle Dirac equation, we derive a universal rule for the relative magnitude of the spin-orbit effect that applies to very different quantum systems, regardless of whether the spin-orbit coupling originates from the strong or electromagnetic interaction. It is shown that in nuclei the near equality of the mass of the nucleon and the difference between the large repulsive and attractive potentials explains the fact that spin-orbit splittings are comparable to the energy spacing between major shells. For a specific ratio between the particle mass and the effective potential whose gradient determines the spin-orbit force, we predict the occurrence of giant spin-orbit energy splittings that dominate the single-particle excitation spectrum.
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    ABSTRACT: We calculate the comprehensive hypernuclear chart for even-even hypernuclei with magic numbers of $\Lambda$'s (for Z $\leq$ 120 and $\Lambda \leq$70) and estimate the number of bound systems, considering the present uncertainties in the $\Lambda-$nucleon and $\Lambda-\Lambda$ interactions. We consider a density functional approach adjusted to microscopic Bruckner-Hartree-Fock calculations, where the $\Lambda\Lambda$ term is corrected in a phenomenological way, to reproduce present experimental constraints. Different models which strongly deviate at large densities, but giving the same bond energy, are generated in order to take into account the uncertainties related to the high density equation of state. The number of bound even-even-even hypernuclei is estimated to 491680 $\pm$ 34400. This relatively low uncertainty is due to the fact that the well constrained low density and highly unconstrained high density behavior of the energy functional turn out to be largely decoupled. Results in hypernuclei appear to be almost independent of the choice for the high-density part of the $\Lambda\Lambda$ interaction. The location of the hyperdriplines is also evaluated. Significant deviations from Iron-Nickel elements can be found for hypernuclei with the largest binding energy per baryon. Proton, neutron and hyperon magicity evolution and triple magic hypernuclei are studied. Possible bubbles and haloes effect in hypernuclei are also discussed. The present results provide a first microscopic evaluation of the hypernuclear landscape.
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    ABSTRACT: Excited states in $^{28}$Na have been studied using the $\beta$-decay of implanted $^{28}$Ne ions at GANIL/LISE as well as the in-beam $\gamma$-ray spectroscopy at the NSCL/S800 facility. New states of positive (J$^{\pi}$=3,4$^+$) and negative (J$^{\pi}$=1-5$^-$) parity are proposed. The former arise from the coupling between 0d$\_{5/2}$ protons and a 0d$\_{3/2}$ neutron, while the latter are due to couplings with 1p$\_{3/2}$ or 0f$\_{7/2}$ neutrons. While the relative energies between the J$^{\pi}$=1-4$^+$ states are well reproduced with the USDA interaction in the N=17 isotones, a progressive shift in the ground state binding energy (by about 500 keV) is observed between $^{26}$F and $^{30}$Al. This points to a possible change in the proton-neutron 0d$\_{5/2}$-0d$\_{3/2}$ effective interaction when moving from stability to the drip line. The presence of J$^{\pi}$=1-4$^-$ negative parity states around 1.5 MeV as well as of a candidate for a J$^{\pi}$=5$^-$ state around 2.5 MeV give further support to the collapse of the N=20 gap and to the inversion between the 0f$\_{7/2}$ and 1p$\_{3/2}$ levels below Z=12. These features are discussed in the framework of Shell Model and EDF calculations, leading to predicted negative parity states in the low energy spectra of the $^{26}$F and $^{25}$O nuclei.
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    ABSTRACT: Giant resonances are collective excitation modes for many-body systems of fermions governed by a mean field, such as the atomic nuclei. The microscopic origin of such modes is the coherence among elementary particle-hole excitations, where a particle is promoted from an occupied state below the Fermi level (hole) to an empty one above the Fermi level (particle). The same coherence is also predicted for the particle–particle and the hole–hole excitations, because of the basic quantum symmetry between particles and holes. In nuclear physics, the giant modes have been widely reported for the particle–hole sector but, despite several attempts, there is no precedent in the particle–particle and hole–hole ones, thus making questionable the aforementioned symmetry assumption. Here we provide experimental indications of the Giant Pairing Vibration, which is the leading particle–particle giant mode. An immediate implication of it is the validation of the particle–hole symmetry.
    Nature Communications 03/2015; 6. DOI:10.1038/ncomms7743 · 10.74 Impact Factor
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    ABSTRACT: Nuclear Energy Density Functionals (EDFs) are a microscopic tool of choice extensively used over the whole chart to successfully describe the properties of atomic nuclei ensuing from their quantum liquid nature. In the last decade, they also have proved their ability to deal with the cluster phenomenon, shedding a new light on its fundamental understanding by treating on an equal footing both quantum liquid and cluster aspects of nuclei. Such a unified microscopic description based on nucleonic degrees of freedom enables to tackle the question pertaining to the origin of the cluster phenomenon and emphasizes intrinsic mechanisms leading to the emergence of clusters in nuclei.
    Journal of Physics Conference Series 12/2014; 569(1). DOI:10.1088/1742-6596/569/1/012028
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    ABSTRACT: Nuclear states are often described as quantum liquid states. Using the localisation parameter, it is possible to understand cluster states in nuclei as hybrid states between quantum liquid and crystal states. Recent calculations discussing the effect of the depth of the confining potential, as well as various lengthscales ratios, are presented in order to provide a complementary view on the cluster phenomenon in nuclei.
    Journal of Physics Conference Series 12/2014; 569(1). DOI:10.1088/1742-6596/569/1/012006
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    ABSTRACT: We study the finite temperature Hartree-Fock-BCS approximation for selected stable Sn nuclei with zero-range Skyrme forces. Hartree Fock BCS approximation allows for a straightforward interpretation of the results since it involves $u$ and $v$'s which are not matrices as in HFB. Pairing transitions from superfluid to the normal state are studied with respect to the temperature. The temperature dependence of the nuclear radii and neutron skin are also analyzed. An increase of proton and neutron radii is obtained in neutron rich nuclei especially above the critical temperature. Using different Skyrme energy functionals, it is found that the correlation between the effective mass in symmetric nuclear matter and the critical temperature depends on the pairing prescription. The temperature dependence of the nucleon effective mass is also investigated, showing that proton and neutron effective masses display different behavior below and above the critical temperature, due to the small temperature dependence of the density.
    European Physical Journal A 10/2014; 50(10):160. DOI:10.1140/epja/i2014-14160-4 · 2.42 Impact Factor
  • E Yüksel, E Khan, K Bozkurt
    Journal of Physics Conference Series 09/2014; 533:012019. DOI:10.1088/1742-6596/533/1/012019
  • Physical Review Letters 07/2014; 113(5). DOI:10.1103/PhysRevLett.113.059902 · 7.73 Impact Factor
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    ABSTRACT: The isoscalar monopole response has been measured in the unstable nucleus ^{68}Ni using inelastic alpha scattering at 50A MeV in inverse kinematics with the active target MAYA at GANIL. The isoscalar giant monopole resonance (ISGMR) centroid was determined to be 21.1±1.9 MeV and indications for a soft monopole mode are provided for the first time at 12.9±1.0 MeV. Analysis of the corresponding angular distributions using distorted-wave-born approximation with random-phase approximation transition densities indicates that the L=0 multipolarity dominates the cross section for the ISGMR and significantly contributes to the low-energy mode. The L=0 part of this low-energy mode, the soft monopole mode, is dominated by neutron excitations. This demonstrates the relevance of inelastic alpha scattering in inverse kinematics in order to probe both the ISGMR and isoscalar soft modes in neutron-rich nuclei.
    Physical Review Letters 07/2014; 113(3):032504. DOI:10.1103/PhysRevLett.113.032504 · 7.73 Impact Factor
  • 07/2014; 78(7):802-804. DOI:10.7868/S0367676514070199
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    ABSTRACT: The magic nature of the $^{54}$Ca nucleus is investigated in the light of the recent experimental results. We employ both HFB and HF+BCS methods using Skyrme-type SLy5, SLy5+T and T44 interactions. The evolution of the single-particle spectra is studied for the N=34 isotones: $^{60}$Fe, $^{58}$Cr, $^{56}$Ti and $^{54}$Ca. An increase is obtained in the neutron spin-orbit splittings of $p$ and $f$ states due to the effect of the tensor force which also makes $^{54}$Ca a magic nucleus candidate. QRPA calculations on top of HF+BCS are performed to investigate the first $J^{\pi}$=$2^{+}$ states of the calcium isotopic chain. A good agreement for excitation energies is obtained when we include the tensor force in the mean-field part of the calculations. The first $2^{+}$ states indicate a subshell closure for both $^{52}$Ca and $^{54}$Ca nuclei. We confirm that the tensor part of the interaction is quite essential in explaining the neutron subshell closure in $^{52}$Ca and $^{54}$Ca nuclei.
    Physical Review C 06/2014; 89(6):064322. DOI:10.1103/PhysRevC.89.064322 · 3.88 Impact Factor
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    ABSTRACT: The framework of nuclear energy density functionals is applied to a study of the formation and evolution of cluster states in nuclei. The relativistic functional DD-ME2 is used in triaxial and reflection-asymmetric relativistic Hartree-Bogoliubov calculations of relatively light $N = Z$ and neutron-rich nuclei. The role of deformation and degeneracy of single-nucleon states in the formation of clusters is analysed, and interesting cluster structures are predicted in excited configurations of Be, C, O, Ne, Mg, Si, S, Ar and Ca $N = Z$ nuclei. Cluster phenomena in neutron-rich nuclei are discussed, and it is shown that in neutron-rich Be and C nuclei cluster states occur as a result of molecular bonding of $\alpha$-particles by the excess neutrons, and also that proton covalent bonding can occur in $^{10}$C.
    Physical Review C 06/2014; 90(5). DOI:10.1103/PhysRevC.90.054329 · 3.88 Impact Factor
  • E. Khan
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    ABSTRACT: Recent results obtained with energy density functional (EDF) based methods are presented, focused on the nuclear phenomenology. EDF approaches aim for an universal description of the nuclear phenomena over the nuclear chart. Achievements from large to small nuclear systems are depicted: equation of state of nuclear matter, heavy and light nuclei. Dynamical aspects such as nuclear excitations, decay and reactions are also presented. EDF methods are progressing towards an unified and systematic description of the rich variety of the nuclear phenomena such as quantum liquid and cluster states, or nuclear structure and reactions.
    The European Physical Journal Conferences 02/2014; 66. DOI:10.1051/epjconf/20146601009
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    ABSTRACT: The role of superfluidity on the symmetry energy and on the incompressibility is studied in nuclear matter and finite nuclei employing Hartree-Fock-Bogoliubov modeling based on several types of pairing interactions (surface, mixed and isovector-density dependent). It is observed that, while pairing has only a marginal effect on the symmetry energy and on the incompressibility at saturation density, the effects are significantly larger at lower densities.
    European Physical Journal A 01/2014; 50(2). DOI:10.1140/epja/i2014-14018-9 · 2.42 Impact Factor
  • Acta Physica Polonica Series B 01/2014; 45(2):437. DOI:10.5506/APhysPolB.45.437 · 1.00 Impact Factor
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    ABSTRACT: The isoscalar monopole response is studied in doubly magic 208Pb, 100,132Sn nuclei using the Skyrme HF+RPA model. A low-energy strength is predicted and corresponds to almost pure single-particle excitations. These pure single-particle excitations allow to analyse the splitting of the corresponding spinorbit partners. A good agreement with the spin-orbit splitting data is found in the case of 208Pb. The experimental width of the giant monopole resonance may hinder the measurement of the soft monopole mode.
    European Physical Journal A 10/2013; 49(124):1-8. DOI:10.1140/epja/i2013-13124-6 · 2.42 Impact Factor
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    ABSTRACT: The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
  • E. Khan, J. Margueron
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    ABSTRACT: Background: The determination of the density dependence of the nuclear incompressibility can be investigated using the isoscalar giant monopole resonance.Purpose: The importance of the so-called crossing density at subsaturation density is underlined.Methods: The measurements of the isoscalar giant monopole resonance (GMR), also called the breathing mode, are analyzed with respect to their constraints on the quantity M_{c}, e.g., the density dependence of the nuclear incompressibility around the so-called crossing density ρ_{c}=0.1 fm^{−3}.Results: The correlation between the centroid of the GMR, E_{GMR}, and M_{c} is shown to be more accurate than the one between E_{GMR} and the incompressibility modulus at saturation density, K_{∞}, giving rise to an improved determination on the nuclear equation of state. The relationship between M_{c} and K_{∞} is given as a function of the skewness parameter Q_{∞} associated with the density dependence of the equation of state. The large variation of Q_{∞} among different energy density functionals directly impacts the knowledge of K_{∞}: A better knowledge of Q_{∞} is required to deduce more accurately K_{∞}. Using the local density approximation, a simple and accurate expression relating E_{GMR} and the quantity M_{c} is derived and successfully compared to the fully microscopic predictions.Conclusions: The measurement of the GMR constrains the slope of the incompressibility M_{c} at the crossing density rather than the incompressibility modulus at the saturation density.
    Physical Review C 09/2013; 88(3). DOI:10.1103/PhysRevC.88.034319 · 3.88 Impact Factor

Publication Stats

1k Citations
283.18 Total Impact Points

Institutions

  • 2004–2014
    • Université Paris-Sud 11
      • Institut de Physique Nucléaire (IPN)
      Orsay, Île-de-France, France
  • 2013
    • Yildiz Technical University
      • Department of Physics
      İstanbul, Istanbul, Turkey
  • 2000–2012
    • Institut de Physique Nucléaire de Lyon
      Lyons, Rhône-Alpes, France
    • University of Milan
      Milano, Lombardy, Italy
  • 2002–2010
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 1998
    • Orsay Physics
      Fuveau, Provence-Alpes-Côte d'Azur, France