Dipole response of exotic nuclei and the EOS Konstanze Boretzky, GSI - PowerPoint PPT Presentation

Dipole response of exotic nuclei and the EOS Konstanze Boretzky, GSI for the LAND-R 3 B Collaboration • low-lying dipole strength �� nuclear matter properties � predictions for relation to symmetry energy parameters • dipole strength in Tin isotopes: � Coulomb excitation in inverse kinematics using LAND-R 3 B � 129-132 Sn � interpretation in terms of symmetry energy for 130 , 132 Sn, 208 Pb • experimental outlook: � decay studies: 68 Ni � dipole strength evolution in proton-rich nuclei � new systematic investigations EQUATION OF STATE Konstanze Boretzky – Emmi workshop July 2010

Dipole response of exotic nuclei and the EOS symmetry energy ( ρ ) 'core' skin EQUATION OF STATE Konstanze Boretzky – Emmi workshop July 2010

Dipole response of exotic nuclei and the EOS symmetry energy ( ρ ) 'core' skin EQUATION OF STATE Konstanze Boretzky – Emmi workshop July 2010

symmetry energy of nuclear matter Taylor expansion per nucleon in nuclear matter : − N Z ρ α = ρ + ρ α 2 + α 4 α = E ( , ) E ( , 0 ) S ( ) Ο ( ) , 2 A K ρ = − + ρ − ρ + 2 E ( , 0 ) a 0 ( ) ... V 0 ρ 2 18 0 ∂ 2 ρ α 1 E ( , ) | ρ = = S ( ) 2 ∂ α 2 2 α = 0 p 0 ∆ p K a 4 = + ρ − ρ + ρ − ρ 2 + a 0 ( ) 0 ( ) ... 4 0 0 ρ ρ 2 2 18 0 0 J = a 4 : Symmetry energy per nucleon in pure neutron matter L ~ p 0 : symmetry energy pressure ∆ K 0 : correction to incompressibility Konstanze Boretzky – Emmi workshop July 2010

symmetry energy S 2 ( ρ ) and neutron skin in 208 Pb B. A. Brown PRL 85 (2000) 5296 & S. Typel & B.A. Brown PRC 64 (2001) 027302 • strong linear correlation between neutron skin and a 4 , p 0 • no distinct correlation to other quantities R.J.Furnstahl NPA 706(2002)85-110 Konstanze Boretzky – Emmi workshop July 2010

pygmy dipole resonance and neutron skin "... ,the pygmy dipole resonance may place important constraints on the neutron skin of heavy nuclei and, as a result, on the equation of state of neutron-rich matter." J. Piekarewicz, PRC 73 (2006) 044325 RRPA (DD-ME2, 132 Sn Σ B PDR (E1)/ Σ B GDR (E1) [%] a 4 =30-38 MeV) neutron skin thickness [fm] RQRPA N.Paar Konstanze Boretzky – Emmi workshop July 2010

Experimental Approach: Electromagnetic excitation at high energies 129-132 Sn, 133,134 Sb 58 Ni, 67-69 Ni b>R P +R T Absorption of Pb ‘virtual Photons’ σ elm ~ Z 2 1 st order pertubation theory: High velocities β ≈ 0.6-0.9 ⇒ High-frequency Fourier components d σ elm / dE = N γ (E) σ γ (E) E γ , max ≈ 18 MeV (for β = 0.8) Konstanze Boretzky – Emmi workshop July 2010

Exp. Approach: Production of fission-fragment beams � Primary: 3*10 8 238 U/spill @550MeV/u � Secondary (mixed): 50 ions 132 Sn/spill (~10/sec @500 MeV/u) ρ A B e = βγ Z m c u B ρ – from position at middle focal plane of the FRS 132 Sn β – from TOF Z – from ∆ E LAND Konstanze Boretzky – Emmi workshop July 2010

Experimental Approach: The LAND reaction setup @ GSI Konstanze Boretzky – Emmi workshop July 2010

Results: even neutron rich Sn isotopes photoneutron cross section σ ( γ ,Xn) [ mb ] 400 124 Sn stabile nucleus 300 (real photons) 200 theoretical Coulomb experimental Coulomb cross section radioactive nucleus cross section 100 (virtual photons) d σ /dE * [ mb/MeV ] σ ( γ ,Xn) [ mb ] 400 300 300 (1n) (2n) (3n) 130 Sn 300 200 200 PDR 200 • position: ~ 10 MeV 100 100 • strength: 100 some % TRK d σ /dE * [ mb/MeV ] σ ( γ ,Xn) [ mb ] Sumrule 400 300 300 (1n) (2n) (3n) 132 Sn • accordance with 300 predictions 200 200 200 GDR 100 100 100 • no deviation from systematics 10 20 10 20 10 20 E * [ MeV ] E * [ MeV ] E * [ MeV ] P. Adrich et al., PRL 95 (2005)132501 Konstanze Boretzky – Emmi workshop July 2010

Low-lying strength in 132 Sn mass region observed in all isotopes difference between even and odd isotopes due to neutron separation threshold location and unpaired neutrons Konstanze Boretzky – Emmi workshop July 2010

Low-lying strength in 132 Sn mass region Konstanze Boretzky – Emmi workshop July 2010

Low-lying strength in 132 Sn mass region real photon measurements at S-Dalinac: N= 82: PLB 542 (2002) 43 208Pb: PRL 89 (2002) 272502 40-48Ca: PRL 93 (2004) 192501 116,124Sn: PRC 57 (1998) 2229 Konstanze Boretzky – Emmi workshop July 2010

Asymmetry parameters and neutron skins from experimental dipole response Σ B PDR (E1)/ Σ B GDR (E1) [ % ] Σ B PDR (E1)/ Σ B GDR (E1) [%] RQRPA calculations 12 130 Sn 132 Sn from 10 < p 0 > = 2.3 ± 0.8 MeV/ fm 3 8 N. Paar 6 < a 4 > = 32.0 ± 1.8 MeV 4 2 0.35 130 Sn 132 Sn R n -R p [ fm ] 0.3 R n -R p [fm] 0.25 R n -R p = 0.23 ± 0.04 fm R n -R p = 0.24 ± 0.04 fm 0.2 0.15 1 2 3 4 5 6 1 2 3 4 5 6 p 0 [MeV/fm 3 ] p 0 [MeV/fm 3 ] p o [ MeV/fm 3 ] p o [ MeV/fm 3 ] A. Klimkiewicz, N. Paar et al., PHYSICAL REVIEW C 76 , 051603(R) (2007) Konstanze Boretzky – Emmi workshop July 2010

neutron skin thickness in Sn isotopes neutron skin thickness [fm] mass number of Sn isotopes stable isotopes: iv. GDR method A.Krasznahorkay et al., NPA 567 (1994) 521-540 radioactive isotopes: PDR/GDR method A. Klimkiewicz et al., PRC 76 (2007) 051603(R) Konstanze Boretzky – Emmi workshop July 2010

208 Pb analysis RQRPA- N.Paar ∑ B pdr (E1)=1.98 e 2 fm 2 from N.Ryezayeva et al., PRL 89(2002)272501 ∑ B gdr (E1)=60.8 e 2 fm 2 from A.Veyssiere et al.,NPA 159(1970)561 a 4 = 31.4 ± 0.8 MeV RQRPA- p 0 = 2.1 ± 0.3 MeV / fm 3 N.Paar δ r = 0.17 ± 0.02 fm A.Krasznahorkay et al. NPA 567(1994)521 C.J.Batty et al. Adv.Nucl.Phys. (1989)1 RQRPA- M.Csatlos et al. NPA 719(2003)C304 N.Paar B.C. Clark et al. PRC 67(2003)044306 our approach Konstanze Boretzky – Emmi workshop July 2010

new contributions/contradictions Konstanze Boretzky – Emmi workshop July 2010

new contributions/contradictions Konstanze Boretzky – Emmi workshop July 2010

open questions • theory: � connection between PDR and symmetry energy parameters? • experiment: � systematics of dipole strength function? (mass, binding energies, asymmetry…) � new more systematic measurements � collectivity? � decay modes (direct gamma and particle decay modes) � role of the particle threshold? � sensitivity above and below threshold for exotic nuclei � connection to measurements for stable nuclei � structure of low-lying strength? � use of different probes, i.e. isoscalar probes � PDR strength in proton-rich nuclei? � adressed in 32 Ar experiment – under analysis Konstanze Boretzky – Emmi workshop July 2010

Isovector and isoscalar electric dipole and quadrupole response of neutron-rich Sn nuclei accepted proposal at GSI What is new? • adress 124 Sn to 134 Sn • higher intensities • higher resolution, better mass reconstruction, less complex detector response system • measurement above and below the neutron threshold • determination of E2 components • excitation via an isoscalar probe using CD 2 target Konstanze Boretzky – Emmi workshop July 2010

Coulombexcitation of 132 Sn on Pb target at 300 and 600 AMeV 2*10 5 events 600 AMeV E1 simulated E2 extracted E1 300 AMeV E2 strength E2 Konstanze Boretzky – Emmi workshop July 2010

proton pygmy predictions N.Paar et al., ≈ 6 % EWSR Phys.Rev.Lett. 94 (2005) 182501 Konstanze Boretzky – Emmi workshop July 2010

Dipole response studies in 32 Ar and 34 Ar statistics expected: ~500 events in PDR region, ~1000 in GDR region 32 Ar 34 Ar ~150 events in PDR region, ~1500 in GDR region Konstanze Boretzky – Emmi workshop July 2010

The LAND-FRS Collaboration 127-132 Sn (Exp. S221) – 57-72 Ni (Exp. S287) Konstanze Boretzky – Emmi workshop July 2010