Nuclear Physics and Astrophysics at the S-DALINAC

1. TU DARMSTADT S-DALINAC GRC 2004 Nuclear Physics and Astrophysics at the S-DALINAC S-DALINAC and its Research Program Giant Resonances – Experiments at Highest Resolution, Wavelets and Scales Electric Dipole Excitations below the Giant Dipole Resonance and their Astrophysical Importance

2. TU DARMSTADT 1 2 3 4 5 A B C D 6 S-DALINAC Experiments at the S-DALINAC 3 – 130 MeV c.w. 1 A 3 C B C D 4 2 5 Status 6 SFB Nuclear resonance fluorescence Polarized electron source Free electron laser Radiation physics 14 MeV bremsstrahlung (e,e´x)-experiments & 180°-spectrometer Photon tagger (e,e´)-experiments 100 MeV bremsstrahl for polarizability of the nucleon Laser experiments and laser for polarized source

4. Scientific goals transverse modes – the nucleus as an elastic medium A: Nuclear Structure fine structure of collective modes mixed-symmetry states nucleosynthesis in the stellar photon bath Nuclear B: neutrino-induced nuclear reactions and supernova models Astrophysics inverse break-up reactions radius of the proton C: Fundamental Experiments polarizability of the proton and deuteron breakup of few-body systems quantum chaos modern many-body methods with correlation dynamics D: development of effective interactions Theory long-range correlations and coupling to the continuum new cavities E: Accelerator energy and intensity upgrade polarized source

5. Charge radius of the proton: new experiment Previous In preparation Spectrometer CH2 Target H2 Gas Target Si Detectors Stanford Mainz Drp/rp < 1%

6. Expected spectrum of recoil protons Measure recoil protons in energy bin → ds/dW as a function of q Efficiency 100% and DW exactly known Take measurements at different E0 and fit GE and GM to it → <rp2>1/2

7. Polarizability of the nucleon: new Compton scattering experiment Previous In preparation Eg´ Eg´ Eg; qg qg qg´ qg´ Ep,d qp,d Liquid H/D target Active high pressure H/D target Background suppression Higher luminosity Expected precision 2.5% (ap) resp. 25% (bp)

8. Experimental setup 1 – Bremstarget 2 – NaJ crystals for gp 3 – High pressure H2 target / 4 – Position sensitive ionization chamber 5 – Quantameter 6 – NaJ monitors for ge ionization chambers

9. Electroinduced deuteron breakup (L + T) cross section LT interference term Potential models fail (Argonne, Bonn, Paris) Test of effective field theories

10. Planned experiments Momentum transfer dependence →sLT (q) 180° scattering → sT Near-threshold behavior TT interference term → sTT (q) Polarized beams

11. Deuteron breakup and primordial nucleosynthesis Deuterium and 7Lisynthesized in Big Bang p(n,g)d d(d,p)t t(a,g)7Li p(n,g)d rate: largest uncertainty for 7Li abundance → Test of cosmological standard model h : baryon / photon ratio

12. Deuteron breakup and primordial nucleosynthesis of 7Li D(e,e‘)Θ = 180°E0 = 25 MeV Reaction D(e,e´): at the threshold Selectivity to M1 component→ measure at 180° Precise knowledge of thecross section necessary → high resolution 0 - 200 keVabove threshold DE ≤ 20 keV EX (MeV)

13. 1954 - 2004: 50 years of inelastic electron scattering on nuclei Discovery of the giant quadrupole resonance (1972) Rotational bands in deformed nuclei and the shape of the ground state (1976) Stretched shell model, p-h states and e. m. transitions up to E12 and M14 (1979) Discovery of the Scissors Mode (1984) Nucleon momentum distribution in (e,e’N) reactions (1990) Excitation and decay of giant resonances in (e,e’x) reactions (since 1990)

14. Discovery of the ISGQR: 140Ce Pitthan and Walcher (Darmstadt, 1972) DL = 2 DT = 0 Centroid energy: Ec ~ 63 A-1/3 MeV Width ? Damping mechanisms ?

15. Fine structure of the ISGQR DE  1 MeV TRIUMF (1981) DE  40 keV iTHEMBA (2004) Fluctuations of different strengths and scales Not a Lorentzian

16. M2 resonance in 180o electron scattering

17. Fine structure of the spin-flip GTR High energy resolution Asymmetric fluctuations

18. Fine structure of giant resonances Search for characteristic energy scales of fluctuations: Entropy index method Local scaling dimension: Aiba, Matsuo (1999) Wavelet analysis

19. Wavelet analysis and Wavelet coefficients:

20. 208Pb(e,e‘) at S-DALINAC Fast and model independent

21. 208Pb(p,p‘) at iThemba LABS

22. Diagrammatic representation of the dissipation mechanisms

23. Scales in the GQR in 208Pb 208Pb(p,p’) E0 = 200 MeV q = 8o QPM QPM collective QPM non-collective Collective part: all scales Non-collective part: no prominent scales

24. Spreading of a GR due to the Coupling to Doorway States and Decay into Compound Nucleus States

25. 48Ca(e,e’n)

26. The photoresponse of atomic nuclei Strength 5 10 15 Energy/MeV Considerable E1 strength is predicted below the 1 region

27. E1 excitations around the particle threshold Nuclear structure phenomenon Fundamental E1 mode below the GDR Importance for understanding of exotic nuclei E1 strength will be shifted to lower energies in neutron rich systems Impact on nucleosynthesis Gamow window for photo-induced reactions in explosive stellar events

28. Impact on nucleosynthesis (g,n) and (g,a) reactions s-process p- or g-process (n,g) / (g,n) equilibrium r-process

29. Origin of the photons Cassiopeia A Temperatures up to 3x109 K ~ 200 keV

30. The photon density T=2.5x109 K typical threshold

31. What is the relevant energy range ? Reaction Rate:

32. Generation of Planck spectra at S-DALINAC A. Zilges et al., Prog. Part. Nucl. Phys. 44 (2000) 39 P. Mohr et al., Phys. Lett. B 488 (2000) 127

33. Photon scattering off 138Ba 138Ba Emax=9.2 MeV 11B E1 excitations A. Zilges et al., Phys. Lett. B 542 (2002) 43

34. E1 strength distribution in N=82 nuclei 138Ba 140Ce 142Nd 144Sm A. Zilges et al., Phys. Lett. B 542 (2002) 43

35. E1 strength distribution in Ca isotopes T. Hartmann et al., PRC 65 (2002) 034301 and to be published T. Hartmann et al., PRL 85 (2000) 274

36. Neutron/proton ″skin″ excitations Oscillations of a neutron or proton rich periphery vs. the core leads to isovector E1 excitations Soft Dipole Mode in exotic nuclei Located around 7 MeV in stable nuclei Up to 1% of EWSR in some stable nuclei → major contribution to the nuclear dipole polarizability see e.g.: J. Chambers et al., Phys. Rev. C 50 (1994) R2671 P. van Isacker et al., Phys. Rev. C 45 (1992) R13

37. Evidence for neutron/proton ″skins″ • Antiproton absorption (LEAR at CERN): • neutron rich nuclear periphery for Sn< 10 MeV • proton rich nuclear periphery for e.g. 144Sm • P. Lubinski et al., Phys. Rev. C 57 (1998) 2962 • R. Schmidt et al., Phys. Rev. C 67 (2003) 044308 • Elastic proton scattering: for many neutron rich nuclei R.H. McCamis et al., Phys. Rev. C 33 (1986) 1624 C.J. Batty et al., Adv. Nucl. Phys. 19 (1989) 1 62 82

38. Evidence for neutron/proton ″skins″ • Isovector spin-dipole resonance (KVI): for neutron rich Sn isotopes A. Krasznahorkay et al., Phys. Rev. Lett. 82 (1999) 3216 • Self-consistent HFB theory for N=82: for Z < 64 for Z > 64 J. Dobaczewski, W. Nazarewicz et al., Z. Phys. A 354 (1996) 27

39. Summed E1 strength in N=82 nuclei neutron rich proton rich

40. QPM calculations for 138Ba experiment (S-DALINAC) theory (QPM) V. Ponomarev, J. Wambach et al., to be published

41. Electric dipole response of neutrons and protons in QPM calculations for 138Ba The E1 strength at 7 MeV is dominantly isoscalar neutrons protons r2r(r) (e fm-1) V. Ponomarev, J. Wambach et al., to be published

42. TU DARMSTADT S-DALINAC Summary An E1 resonance exhausting up to 1% of the EWSR is observed in all examined nuclei around about 7 MeV We still do not know its systematics, isospin character, decay pattern, and form factor It is of great astrophysical importance for (n,g) / (g,n) equilibrium in explosive nucleosynthesis Acknowledgements J. Enders, Y. Kalmykov, P. von Neumann-Cosel, V. Ponomarev, G. Schrieder, A. Shevchenko, J. Wambach, A. Zilges Darmstadt / iThembaLAB / Osaka / UCT / Wits Collaborations