Giant Resonances in Exotic Nuclei Experimental Status and Perspectives Thomas Aumann Gesellschaft für Schwerionenforschung INPC 2007 Tokyo, June 6 th 2007 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

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

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

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

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

Experimental Tool: Electromagnetic excitation at high energies High velocities v/c   High-frequency Fourier components E ,max  25 MeV 1 GeV/u) b>R P +R T Pb Absorption of ‘virtual Photons’  elm ~ Z 2 Semi-classical theory: d  elm / dE = N  (E)   (E) Determination of ‘photon energy’ (excitation energy) via a kinematically complete measurement of the momenta of all outgoing particles (invariant mass) adiabatic cut-off:

Experimental Approach: Production of (fission-)fragment beams Bρ – from position at middle focal plane of the FRS β – from TOF Z – from ΔE LAND  Primary: 3*  Secondary (mixed): 50 ions 132 Sn/spill MeV/u) 132 Sn

Experimental Scheme: The LAND reaction Excitation energy E * from kinematically complete measurement of all outgoing particles: Neutrons ToF,  E LAND tracking → B  A/Q  Charged fragments Photons ALADIN large-acceptance dipole ToF, x, y, z Crystal Ball and Target Beam projectile tracking ~12 m Mixed beam

Dipole-strength distributions in neutron-rich Sn isotopes Electromagnetic-excitation cross section Photo-neutron cross section P. Adrich et al., PRL 95 (2005) stable radioactive A PDR GDR E centr [MeV] sum rule fraction [%] E centr [MeV] Γ [MeV] sum rule fraction [%] 124 Sn Sn 10.1 (0.7) 7.0 (3.0) 15.9 (0.5) 4.8 (1.8) 145 (19) 132 Sn 9.8 (0.7) 4.0 (3.1) 16.1 (0.8) 4.7 (2.2) 125 (32) PDR located at 10 MeV exhausts a few % TRK sum rule in agreement with theory GDR no deviation from systematics

Low-lying strength in 132 Sn mass neighborhood odd nuclei allow extending ( ,n) measurements to lower excitation energies → comparison to (  ') data for stable isotopes 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) 5 MeV < E* < 9 MeV A. Klimkiewicz et al, submitted to PRL

Symmetry energy S 2 (ρ) and neutron skin in 208 Pb strong linear correlation between neutron skin thickness and parameters a 4, p 0 R.J.Furnstahl NPA 706(2002) Alex Brown, PRL 85 (2000) 5296

Theory: Precise knowledge of neutron-skin thickness could constrain the density dependence of S(  ) 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, (2006)) Here: Quantitative attempt by means of RHB + RQRPA, (density-dependent meson-exchange DD-ME ) Paar, Vretenar, Ring et al. (Phys. Rev. C67, (2003)) Symmetry energy and neutron skin form dipole strength

RQRPA – DD-ME N. Paar et al. Result ( averaged 130,132 Sn) : a 4 = 32.0 ± 1.8 MeV p o = 2.3 ± 0.8 MeV/fm 3 PDR strength versus a 4, p o S(  ) : moderate stiffness

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

Euroball 15 Clusters Located at 16.5°, 33°, 36° degrees Energetic threshold ~ 100 keV Hector BaF 2 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) RISING 4 CsI 9 Si

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

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

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

Target-Recoil and Gamma Detector around internal target Target-Recoil and Gamma Detector around internal target NESR EXL Exotic Nuclei Studied in Light-Ion Induced Reactions at NESR Internal target

ELISe The Electron-Ion (eA) Collider Electron spectrometer  p/p=10 -4 gap 25 cm weight 90 t Electron spectrometer  p/p=10 -4 gap 25 cm weight 90 t

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

26 cm 20 cm 28 cm 56 Ni 50 A.MeV 10 4 pps GANIL: GMR & GQR in the unstable 56 Ni 56 GANIL Active Target MAYA C. Monrozeau et al., Nucl. Phys. A 788, 182c (2007)

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 130,132 Sn 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 of dipole strength in neutron-proton asymmetric nuclei Theory+experiment: Relation of low-lying dipole strength to symmetry energy and neutron skin Decay characteristics (e.g.,  decay branch) ( ,  ') in 68 Ni (RISING → F. Camera, F8-2), ( ,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)

The LAND/FRS collaboration S221 Uni Frankfurt Th.W. Elze R. Palit Uni Krakow P. Adrich A. Klimkiewicz R. Kulessa G. Surówka W. Walus Uni Mainz J.V. Kratz C. Nociforo 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 Santiago de Compostela D. Cortina-Gil

208 Pb analysis R n – R p = 0.18 ± fm ∑B pdr (E1)=1.98 e 2 fm 2 from N.Ryezayeva et al., PRL 89(2002) ∑B gdr (E1)=60.8 e 2 fm 2 from A.Veyssiere et al.,NPA 159(1970)561 RQRPA- N.Paar LAND C.Satlos et al. NPA 719(2003)304 A.Krasznahorkay et al. NPA 567(1994)521 C.J.Batty et al. Adv.Nucl.Phys. (1989)1 B.C. Clark et al. PRC 67(2003)044306