PYGMY DIPOLE RESONANCE IN A SCHEMATIC MODEL

1. PYGMY DIPOLE RESONANCE IN A SCHEMATIC MODEL AndreeaCroitoru University of Bucharest ROMANIA Braşov 2014

3. For further information please see • Prof. Virgil Băran’s presentation • on Thursday

6. Collective motions in nuclei GDR

7. Giant Dipole Resonance in Nuclear Systems protons Photoreaction cross-section for Au (A=197) neutrons

8. Macroscopic pictures for the Giant Dipole Resonance

9. What happens below 10 MeV?

12. Motivation • Information • about the shapes of • nuclei and excited states • Information about the symmetry energy and EOS • Influence in nucleosynthesis processes • Relation with the neutron skin thickness

14. A schematic model for GDR

15. G-T macroscopic picture for GDR For We can split therefore

16. G-T macroscopicpicture for GDR n p Proton sphere Neutron sphere

17. …but there is a problem The GDR described by PROBLEM has

18. G-T macroscopic picture for GDR Beyond Brink PROBLEM SOLVED What if We still can separate Where the coupling parameter is related to the (potential) symmetry energy

19. From a “Giant” to a “Pygmy”

20. A schematic model for PDR Considering three subsystems: neutron core, proton core, neutron in excess we can still separate into But there are two problems…

21. …first problem PROBLEM EPDR <10MeV EGDR >15MeV Core Hamiltonian: Pygmy Hamiltonian: xc Both modes have energy ! Y

22. …and second problem PROBLEM Experiment ~ 0.04 Overestimation of exp. data for Nc=Z!

23. Solving the overestimation of EWSR: Vlasov approach Better… But Ne=?

24. obtained using Vlasov approach.

25. Solving the energy problem: Generalization of D-D residual interaction But what if with

28. Coupled modes nc pc pc, nc Core neutrons and protons sphere Proton sphere Excess neutrons Core neutron sphere Neutron sphere

29. The quest for normal modes

30. BEHOLD :

32. PREDICTS TWO NORMAL MODES X1: Xc and Y in phase X2: Xc and Y out of phase AGREEMENT WITH EGDR_exp=17.1 MeV, EPDR_exp=9.55 MeV(Rossi et al PRL(2013)242503) AGREEMENT WITH f2_exp=0.028 (Rossi et al PRL(2013)242503)

33. n nc pc pc, nc ne n n pc pc nc nc ne ne

34. The structure of the normal modes from Vlasov simulation (see V. Băran)

35. So… • The HOSM+Vres is a useful tool in offering a microscopic descriptionof the PDR and the GDR (centroidenergy, sum rule) and a picture of nucleon vibrations in the PDR • The EWSR exhausted by the pygmy mode overestimates the experimental data if Nc=Z • A better result is obtained for a more stable core Nc>Z • But…For a more accurate picture we needmicroscopic self-consistent models

36. Thank you !

38. CRITICAL QUESTIONS

40. xc Y

42. A schematic model for PDR Applying the Thomas-Reiche-Kuhn sum rule we obtain with and

43. A GENERALIZATION OF THE DIPOLE-DIPOLE RESIDUAL INTERACTION