1. 1 Di-Neutron Correlation in Soft Octupole Excitations of Medium-Mass Nuclei near Drip-Line Y. Serizawa and M. Matsuo Niigata Univ.

2. 2 Introduction - Hyperspherical harmonics method - 3-body model - HFB O, Ca, Ni: Matsuo et al., PRC71 (2005) 064326. 11 Li: Bertsch, Esbensen, Ann.Phys.209(1991)327. 6 He, 11 Li, 24 O: Hagino, Sagawa, PRC72(2005)044321. 6 He, 11 Li: Zhukov et al., Phys.Rep.231(1993)151. The di-neutron correlation has been discussed with various theoretical approaches. 9 Li neutron halo nn 84 Ni 11 Li

3. 3 Motivation Di-Neutron correlation appears in soft dipole excitations of medium- mass nuclei near drip-line. M. Matsuo et al., PRC71(2005)064326. We investigate the pairing effect in the soft octupole excitations of medium- mass nuclei near the neutron drip-line. Purpose: Does the di-neutron correlation appears in the other multipole excitations? Motivation: I. Hamamoto et al., PRC64, 024313 (2001), X.R. Zhou et al., NPA723, 375 (2003). - Study by using continuum RPA:

4. 4 Method M. Matsuo NPA696, 371 (2001). - Both continuum and pairing are treated in descriptions of excited states. - Appropriate to study the di-neutron dynamics. We use the continuum QRPA.

5. 5 Model Hamiltonian ph channel pp channel Mean-fieldselfconsistent HF potential with Skyrme force SLy4 Density-dependent delta int. QRPA residual int. Skyrme force with Landau-Migdal approx. (t0 and t3 term are exactly treated) Mixed pairing

6. 6 IS Octupole Strength Functions ISneutronproton (1) The low-lying octupole state (corresponds to the sharp peak) arrows: 1, 2-neutron threshold

7. 7 IS Octupole Strength Functions arrows: 1, 2-neutron threshold ISneutronproton (2) The neutron mode (corresponds to the broad bump) - is seem to be peculiar to near-drip-line nuclei. - develops as we approach the drip line.

8. 8 Dominant ph collective surface vibrational mode Transition Densities Full No dynamical pairing Neutron-pair transition density ph transition density Significant tail in pp channel Large effect of dynamical pairing (1)(2) 84 Ni (2) (1)

9. 9 lcut for transition densities O l=9 l=7 l=13 Full (l=17) No dynamical l=11 The high-l orbits essentially contribute to the neutron-pair transition density. Di-neutron correlation appears in soft octupole excitations. l=15 84 Ni

10. 10 Neutron-number dependence The di-neutron correlation is more significant as we approarch the neutron drip line.

11. 11 Comparison with Soft Dipole Excitations l=7 full No dynamical l=5 … dipole octupole 84 Ni Transition densities [arb.unit] The di-neutron correlation is more clear in the soft dipole excitations.

12. 12 Model Dependences Di-neutron correlation appears more significant as shallower Fermi level. Features of the di-neutron correlation are sensitive to depth of Fermi surface.

13. 13 Summary The di-neutron correlation appears in the soft octupole excitations. By using the continuum QRPA method, we investigate the soft octupole excitations of medium-mass nuclei near the neutron drip line. Result: - The di-neutron correlation is less clear than the soft dipole excitations. - The di-neutron correlation is more significant as we approarch the neutron drip line. - The features of the di-neutron correlation are sensitive to depth of the Fermi surface.