Giant Resonances in Exotic Nuclei Experimental Status and Perspectives

1. Giant Resonances in Exotic NucleiExperimental Status and Perspectives Thomas Aumann Gesellschaft für Schwerionenforschung INPC 2007 Tokyo, June 6th2007 • Introduction • The dipole response of neutron-rich nuclei • - Coulomb breakup of halo nuclei • - Giant and Pygmy collective excitations • - Asymmetry energy and neutron skin • Future perspectives

2. The collective response of the nucleus: Giant Resonances 65Cu 120Sn Berman and Fulz, Rev. Mod. Phys. 47 (1975) 47 208Pb Electric giant resonances Photo-neutron cross sections Isoscalar Isovector Monopole (GMR) Dipole (GDR) Quadrupole (GQR)

3. The dipole response of neutron-rich nuclei Stable nuclei: 100% of the E1 strength absorbed into the Giant Dipole Resonance (GDR) 120Sn ! threshold strength non-resonant transitions 11Be The one-neutron Halo spectroscopic tool: Neutron-Proton asymmetric nuclei: low-lying dipole strength

4. Two-neutron Halos: Correlations RIKEN Data on 11Li |(6He)|2 n-n distance (fm) core-nn distance (fm) Calculation for 6He: Danilin Non-energy weighted sum rule → T. Nakamura, F7-1 T. Nakamura et al., Phys. Rev. Lett. 96 (2006) 252502.

5. The dipole response of neutron-rich nuclei Stable nuclei: 100% of the E1 strength absorbed into the Giant Dipole Resonance (GDR) 120Sn ! threshold strength ! strong fragmentation ? new collective soft dipole mode (Pygmy resonance) non-resonant transitions 16O Prediction: RMF (N. Paar et al.) 11Be The one-neutron Halo 20O 132Sn 22O spectroscopic tool: Neutron-Proton asymmetric nuclei: low-lying dipole strength

6. Experimental Tool: Electromagnetic excitation at high energies b>RP+RT Absorption of ‘virtual Photons’ Pb selm ~ Z2 Semi-classical theory: dselm/ dE = Ng(E) sg(E) adiabatic cut-off: High velocities v/c0.6-0.9  High-frequency Fourier components Eg,max  25 MeV (@ 1 GeV/u) Determination of ‘photon energy’ (excitation energy) via a kinematically complete measurement of the momenta of all outgoing particles (invariant mass)

7. Experimental Approach: Production of (fission-)fragment beams • Primary: 3*108238U/spill @550MeV/u • Secondary (mixed): 50 ions132Sn/spill (~10/sec @500 MeV/u) Bρ – from position at middle focal plane of the FRS 132Sn β – from TOF Z – from ΔE LAND

8. Experimental Scheme: The LAND reaction setup @GSI Mixed beam Charged fragments ToF, DE LAND tracking → Br ~ A/Qbg Neutrons ToF, x, y, z ~12 m projectile tracking Photons ALADIN large-acceptance dipole Crystal Ball and Target Beam Excitation energy E*from kinematically complete measurement of all outgoing particles:

9. Dipole-strength distributions in neutron-rich Sn isotopes Electromagnetic-excitation cross section Photo-neutron cross section stable radioactive • PDR • located at 10 MeV • exhausts a few % TRK sum rule • in agreement with theory • GDR • no deviation from systematics P. Adrich et al., PRL 95 (2005) 132501

10. Low-lying strength in 132Sn mass neighborhood odd nuclei allow extending (g,n) measurements to lower excitation energies → comparison to (g,g') data for stable isotopes 5 MeV < E* < 9 MeV Stable nuclei, Photoabsorption, from: A.Zilges et al., Phys.Lett. B 542,43 (2003) S.Volz et al., Nucl.Phys. A 779, 1 (2006) N. Ryezayeva et al., Phys.Rev.Lett. 89 (2002) K. Govaert et al., Phys. Rev. C 57,2229 (1998) A. Klimkiewicz et al, submitted to PRL

11. Symmetry energy S2(ρ) and neutron skin in 208Pb Alex Brown, PRL 85 (2000) 5296 R.J.Furnstahl NPA 706(2002)85-110 • strong linear correlation between neutron skin thickness and parameters a4, p0

12. Symmetry energy and neutron skin form dipole strength Theory: Precise knowledge of neutron-skin thickness could constrain the density dependence of S(r) Work Hypothesis: Pygmy-Strength (since related to skin) should do the same job, but, experimentally, is accessed much easier ! Inspired by recent article of Piekarewicz (Phys. Rev. C 73 , 044325 (2006)) Here: Quantitative attempt by means of RHB + RQRPA, (density-dependent meson-exchange DD-ME ) Paar, Vretenar, Ring et al. (Phys. Rev. C67, 34312 (2003))

13. PDR strength versus a4, po Result (averaged 130,132Sn) : a4 = 32.0 ± 1.8 MeV po = 2.3 ± 0.8 MeV/fm3 RQRPA – DD-ME N. Paar et al. S(r) : moderate stiffness

14. Neutron skin thickness Sn isotopes δr LAND A.Krasznahorkay et al. PRL 82(1999)3216 Rn-Rp Rn – Rp : 130Sn: 0.23 ± 0.04 fm 132Sn: 0.24 ± 0.04 fm A. Klimkiewicz, N. Paar, et al, submitted to PRL

15. RISING ARRAY @GSI Euroball 15 Clusters Located at 16.5°, 33°, 36° degrees Energetic threshold ~ 100 keV Hector BaF2 Located at 142° and 90° degrees Energetic threshold ~ 1.5 MeV Miniball segmented detectors Located at 46°, 60°, 80°, 90°degrees Energetic threshold ~ 100 keV Beam identification and tracking detectors Before and after the target Calorimeter Telescope for beam identification (CATE) 4 CsI 9 Si

16. Preliminary Preliminary Preliminary GEANT Simulations Coulomb excitation of 68Ni (600 MeV A) A structure appears at 10-11 MeV in all detector types F. Camera et al, see F8-2 (g,n) data from LAND under analysis

17. The collective response of the nucleus: Giant Resonances 65Cu 120Sn Berman and Fulz, Rev. Mod. Phys. 47 (1975) 47 208Pb Electric giant resonances Photo-neutron cross sections Isoscalar Isovector Monopole (GMR) Dipole (GDR) Quadrupole (GQR)

18. In-Ring Experiments: Light-Hadron Scattering • Elastic (p,p) … • Inelastic (p,p’), (a,a’) ... • Charge exchange: (p,n), (3He,t) ... • Quasifree (p,pn), (p,2p), (p, pa) ... • Selective to SPIN-ISOSPIN (DS,DT) excitations : • Giant resonances: Monopole.., GT... isoscalar / isovector • Low-lying collective modes • single-particle spectr. factors • nucleon-nucleon correlations, clusters Experimental challenge: Formfactor (DL) at low momentum transfer in inverse kinematics  Storage Ring

19. Target-Recoil and Gamma Detector around internal target EXLExotic Nuclei Studied in Light-Ion Induced Reactions at NESR Internal target NESR

20. ELISeThe Electron-Ion (eA) Collider Electron spectrometer Dp/p=10-4 gap 25 cm weight 90 t

21. RIKEN: Isoscalar excitations in 14O RIKEN: 60 MeV/u 14O on liquid He target Preliminary analysis: COMEX 2006, Nucl. Phys. A 788 (2007) 188c

22. 28 cm 26 cm 20 cm GANIL: GMR & GQR in the unstable 56Ni C. Monrozeau et al., Nucl. Phys. A 788, 182c (2007) 56Ni(d,d’) @ GANIL Active Target MAYA 56Ni 50 A.MeV 104 pps

23. Conclusion Low-lying dipole strength observed in light and medium-mass neutron-rich nuclei (→ D. Beaumel, F5-5) Threshold strength (halo nuclei) established as spectroscopic tool (→ T. Nakamura, F7-1) Peak-like structure below the GDR in 130,132Sn at about 10 MeV excitation energy exhausting about 5% of the energy-weighted sum rule Parameters of GDR in agreement with systematic trends derived from stable nuclei Symmetry energy and neutron-skin thickness from dipole strength: a first attempt Outlook: Systematic measurements ofdipole strength in neutron-proton asymmetric nuclei Theory+experiment: Relation of low-lying dipole strength to symmetry energy and neutron skin Decay characteristics (e.g., g decay branch) (g,g') in 68Ni (RISING →F. Camera, F8-2), (g,n) with LAND setup Monopole and quadrupole strength: active target (GANIL), liquid He (RIKEN, → H. Baba QW-022), internal gas target in a storage ring (GSI, FAIR)

24. The LAND/FRS collaboration S221 Uni Krakow P. Adrich A. Klimkiewicz R. Kulessa G. Surówka W. Walus Uni Frankfurt Th.W. Elze R. Palit Uni Mainz J.V. Kratz C. Nociforo Santiago de Compostela D. Cortina-Gil GSI T. Aumann K. Boretzky H. Emling M. Fallot H. Geissel U. D. Pramanik M. Hellström K.L. Jones Y. Leifels H. Simon K. Sümmerer

25. 208Pb analysis RQRPA-N.Paar RQRPA-N.Paar A.Krasznahorkay et al. NPA 567(1994)521 C.J.Batty et al. Adv.Nucl.Phys. (1989)1 C.Satlos et al. NPA 719(2003)304 RQRPA-N.Paar B.C. Clark et al. PRC 67(2003)044306 LAND ∑Bpdr(E1)=1.98 e2 fm2 from N.Ryezayeva et al., PRL 89(2002)272501 ∑Bgdr(E1)=60.8 e2 fm2 from A.Veyssiere et al.,NPA 159(1970)561 Rn – Rp= 0.18 ± 0.035 fm