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^⋆

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 scattering for momentum transfers 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 reactions is predominantly of transversal nature for scattering angles . Being thus mediated by the convection and spin nuclear currents, the like the reaction, may provide additional information to the one obtained from Coulomb and hadronic excitations of the PDR in , , and heavy-ion scattering reactions. The calculations predict that the 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.