Excitation of the electric pygmy dipole resonance by inelastic electron scattering⋆

V. Yu. Ponomarev; D. H. Jakubassa-Amundsen; A. Richter; J. Wambach

doi:10.1140/epja/i2019-12784-4

EPJ

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2023 Impact factor 2.6

Hadrons and Nuclei

Giant, Pygmy, Pairing Resonances and Related Topics

Eur. Phys. J. A (2019) 55: 236
https://doi.org/10.1140/epja/i2019-12784-4

Regular Article - Theoretical Physics

Excitation of the electric pygmy dipole resonance by inelastic electron scattering^⋆

V. Yu. Ponomarev¹^*, D. H. Jakubassa-Amundsen², A. Richter¹ and J. Wambach¹^,3

¹ Institut für Kernphysik, Technische Universität Darmstadt, D-64289, Darmstadt, Germany
² Mathematisches Institut, Universität München, Theresienstraße 39, D-80333, München, Germany
³ European Centre for Theoretical Studies in Nuclear Physics and related Areas (ECT*) and Fondazione Bruno Kessler, Villa Tambosi, 38123, Villazzano (TN), Italy

^* e-mail: ponomare@theorie.ikp.physik.tu-darmstadt.de

Received: 14 April 2019
Accepted: 27 May 2019
Published online: 3 December 2019

Abstract

To complete earlier studies of the properties of the electric pygmy dipole resonance (PDR) obtained in various nuclear reactions, the excitation of the 1^- states in ¹⁴⁰Ce by $ (e,e')$ scattering for momentum transfers $q = 0.1\mbox{--}1.2$ fm^-1 is calculated within the plane-wave and distorted-wave Born approximations. The excited states of the nucleus are described within the Quasiparticle Random Phase Approximation (QRPA), but also within the Quasiparticle-Phonon Model (QPM) by accounting for the coupling to complex configurations. It is demonstrated that the excitation mechanism of the PDR states in $ (e,e')$ reactions is predominantly of transversal nature for scattering angles $\theta_e \approx 90^{\circ}\mbox{--}180^{\circ}$ . Being thus mediated by the convection and spin nuclear currents, the like the $(\gamma,\gamma')$ reaction, may provide additional information to the one obtained from Coulomb and hadronic excitations of the PDR in $ (p,p')$ , $(\alpha,\alpha')$ , and heavy-ion scattering reactions. The calculations predict that the $ (e,e')$ cross sections for the strongest individual PDR states are in general about three orders of magnitude smaller as compared to the one of the lowest 2⁺ ₁ state for the studied kinematics, but that they may become dominant at extreme backward angles.