Search for PDR in neutron rich nuclei below and above the threshold. O. Wieland

Transcription

1 Search for PDR in neutron rich nuclei below and above the threshold O. Wieland SUNFLOWER WORKSHOP September 11, 2013

2 OUTLINE Introduction and «replay» of past data and analysis Plan to couple DALI2 and 8 large Volume LaBr 3 :Ce detectors and ZDS Plan to use DALI2+LaBr 3 :Ce together with SAMURAI Possible Physics cases 1. PDR in the Ni chain, ( 72 or 74 Ni with 86 Kr Beam) PDR properties, neutron radius 2. PDR in the Ca chain (-> 52 Ca with 70 Zn Beam), dito 3. PDR in the Zr chain, ( 10X Zr) PDR in deformed nuclei, dito 4. PDR in the Fe chain, PDR nearby Ni ( 66,8 Fe 68 Ni n=40,a=68), dito

3 GIANT RESONANCES IN NUCLEI Observables (E*, J,... dependend): Centroid, Width, Strength, Lineshape Information on nuclear structure SUM rules IVGDR Symmetry energy, damping, collectivity, deformation

4 Photoabsorption cross section (a.u.) Pygmy Dipole Resonance Collective oscillation of neutron skin against the core -Level of collectivity? -How (collective) properties change with n? -How isospin changes mean field? -In exotic nuclei: does PDR strength exist also below neutron threshold? -No High resolution/statistics measurements available -Various nuclei and mass regions -Effect of deformation? -Proton Pygmy, still to proof (2008Land?) - Picture of PDR? From Experiment 0 20 Gamma Energy [MeV] E1 strength shifted Towards lower energy From Theory RQTBA dipole transition densities for 68 Ni P. Adrich et al., Phys. Rev. Lett. 95, (2005) J. Gibelin et al., Phys. Rev. Lett. 101, (2008) O.Wieland et al. PRL 102, (2009) refernces therein and cited by Neutrons Protons Litvinova 2012

5 Neutron Skins Pygmy Resonance Neutron stars INPC 2013 Nucl. Astrophysics session:..whole E1 strenght, below and above threshold, from comparable experiments, is urgently needed for exotic nuclei? EOS The PDR strenght gives measure of neutron skin radius. Carbone et al. Phys. Rev. C 81, (R) (2010) Relation between neutron skin and neutron stars : both are built on neutron rich nuclear matter so that one-to-one correlations can be drawn. Yet both radii depend on the knowledge of equation of state of neutron rich matter. Pygmy Resonance in exotic nuclei may have an very important impact on the r-process Nucleosynthesis and on nuclear phenomenology Nupecc long range plan Giant resonances are of paramount importantce for nuclear astrophysics It is of particular interest to study the collective strength in short-lived nuclei

6 Features of this mode There is a trend of the strength to increase with the proton-toneutron asymmetry 40 Ca 0.025% EWSR 48 Ca 0.29% EWSR Stable nuclei photon scattering,photoabsorption (g,g ),(g,n) T. Hartmann PRL85(2000)274 Exotic nuclei? Features How to measure?

7 How to excite and measure this mode in exotic nuclei??.):coulomb break-up (above S n ) 26 Ne LAND at GSI Adrich et al. PRL 95(2005) R3B RIKEN experiment at 58 MeV/u Measured and extracted pygmy with 4.9 (+/- 1.6) % EWSR (45mbarn) Future: SAMURAI, Shogun@RIKEN..R3B@GSI But for astrophysical (g,n)(n,g) not so important above threshold As below and arround

8 2.) Photon scattering technique High selectivity for dipole excitation!! q < q max Photon excitation and decay of GDR - PYGMY b > b min Virtual photon g emission g d C de * 1 N ( E*) E * g g To excite Dipole states one needs: - High beam energy - Large cross sections - Large GDR / GQR ratio ( E*) Vitturi PJP Coulex GDR Ground state decay branching ratio ~ 2% measured on 208 Pb To Select projectile PDR one needs: - High beam energy - Large Doppler effects Background REDUCTION - Good Z proj /Z target ratio n-knockout some mbarn for ( GDR) Ni : 20 ( GQR ) T.Aumann et al EPJ 26(2005)441

9 Low-lying E1 (PDR) Systematic Calculation of Electric Dipole Strengths with Fully Self-consistent Skyrme RPA Sn INAKURA Tsunenori (Tsukuba) NAKATSUKASA Takashi (RIKEN) YABANA Kazuhiro (Tsukuba) 2010 Calculated by Inakura (RIKEN) Method: PRC 80, (2009); PRC 76, (2007) Measurments in neutron rich unstable nuclei

10 High resolution g-spectroscopy at the FRS of GSI 68 Ni beam by fragmentation of MeV/u on Be target (4g/cm 2 ): ppspill 86 Kr, Spill length 6s,period 10 s FRS provides secondary radioactive ion beams Calorimeter Telescope for beam identification CATE Position sensitive 2g/cm 2 Au

11 d /de [mb/mev] Relativistic Coulomb excitation is directly proportional to the Photonuclear cross section. [ Eisenberg,Greiner, Bertulani, Baur, Alder,Winther, Weizsaecker, Williams ] d C g de 68 Ni ANALYSIS of Experiment at GSI (RISING-Setup) (+LAND/R3B) g 1 RF Ng ( Eg ) g ( Eg ) Rg ( Eg ) Eg ResponseFunction LAND / R3B setup: PDR in 68Ni (2005) 1n and 2n and gamma-ray detection DATA give: Preliminary PDR 4.1% g-gs-branching 4.7% 10 3 VP virtual photons gbranching VP and R g PDR Analysis Photonuclear cross section GDR To be Folded with the detector response function! MEASURED PDR 4.7%+/-1.5 GDR 4% stat mod+ld GS Branching (LD) (g,n) GDR PDR Total without pygmy E g [MeV] Dominic Rossi NUPECC LONG RANGE PLAN 2010 [mb] 90 cts in one week O.Wieland et al. PRL 102, (2009)

12 Analysis of the strength/results in 68 Ni

13 Compare strength of pygmy in 68 Ni with theory Note that the shape and strengh depends on the effective force Calculations of different types are available: Microscopic Hartree-Fock + random phase approximation [A.Carbone et al. PRC 81, (R) (2010)] Relativistic Quasi particle Random Phase approximation [Vretenar, Paar,Ring et al.,npa692, 496.]

14 Compare the strength in 68 Ni with Sn data Lower value of the B(E1) in 68 Ni as compare to the Sn region 68 Ni This is consistent with the fact that (N-Z) 2 /A 2 is smaller (N-Z) 2 /A 2 governs the symmetry energy in finite nuclei This is the first hint that from the strength of the pygmy one could get information on the symmetry energy

15 The density dependence of the symmetry energy is poorly constrained and one would like to know the key parameters!!! Nuclear matter EOS Symmetric matter EOS Symmetry energy S The symmetry energy is associated with the exchange of protons into neutrons, and E/A in neutron matter is E/A in symmetric matter plus S! E(ρ,δ) = E 0 (ρ,δ=0) + S(ρ)δ 2 + O(δ 4 ) S(ρ) = J + L/3 ((ρ- ρ 0 )/ρ 0 ) + K sym ((ρ- ρ 0 )/ ρ 0 ) 2 +. Expansion around density with ρ 0 = saturation density L slope parameter K sym curvature parameter at saturation density

16 Possible Correlation that connects L and the PDR strenght Carbone et al. Phys. Rev. C 81, (R) (2010) Predicted Strength Of PDR For different Forces (L) 1,2,3,..19 Skyrme forces 20, 26 RMF (meson exchange) Lagrangians

17 B.A. Brown, PRL 85, 5296 (2000); S. Typel and B.A. Brown, PRC 64, (R) (2001). R.J. Furnstahl, NPA 706, 85 (2002); S. Yoshida and H. Sagawa, PRC 69, (2004). Exp. values from O. Wieland et al., PRL 102, (2009); A. Klimkiewicz et al., PRC 76, (R) (2007). RPA & RRPA Correlations between L and ΔR (the neutron skin thickness) have been noticed previously. (L=slope parameter of symmetry energy at saturation) The idea has been previously presented, and exploited in part (Furnstahl,. Klimkiewicz et al.) However, here for the first time the approach has been pursued with different nuclei and many different classes of EDFs. Carbone et al. Phys. Rev. C 81, (R) (2010)

18 Comparison with other ways of constraining L Possible approach of extracting L (derivative of symmetry energie) from the PDR strenght Contraints on the symmetry energy in agreement with heavy ion fragmentation and with Anti-proton BUT: MORE DATA ARE NEEDED [THIS WORK] A. Carbone et al., Phys. Rev. C 81, (R) (2010) [9] M. B. Tsang et al., Phys. Rev. Lett. 102, (2009). [10] D. V. Shetty et al., Phys. Rev. C76, (2007). [8] L. W. Chen et al., Phys. Rev. Lett. 94, (2005). [26] P. Danielewicz, Nucl. Phys. A727, 233 (2003). [25] P. Danielewicz and J. Lee, Nucl. Phys. A818, 36 (2009). [11] M. Centelles et al., Phys. Rev. Lett. 102, (2009);M. Warda et al., Phys. Rev. C80, (2009). [6] A. Klimkiewicz et al., Phys. Rev. C76, (R) (2007).

19 Inakura: - correlation 0.84 for 68Ni different forces and integrating over PDR! arxiv: v1 June 2013

20 Next STEPS

21 aims in measureing the PDR in 64Fe and neutron skin (following 2005 experiment on 68 Ni) 400AMeV b=0.715 Target 1gPb/cm^2 -> beta=0.706 Predictions: RPA(Skl2,SLY5, ) calculations for 64 Fe. GDR S430 PDR in 64Fe 1n LISE++

22 Next FUTURE STEPS at RIKEN SUNFLOWER

23 Theoretical Predictions PDR PDR PDR PDR Elena Litvinova, Peter Ring and Victor Tselyaev RQTBA-2 Phys. Rev. Lett. 105, (2010) the 70;72 Ni isotopes can be suggested for future measurements. E.Litvinova et al, PRC 79, (2009) PHOTON SCATTERNING POSSIBLE ONLY AT RIKEN +possibly (Lower states 1-,2+,. (large scale) Shell model Calculations to be done (in 68 Ni K. Langanke,) G. A. Lalazissis, et al. Phys.Lett. B 647,111(2007) Neutron SKIN 70 Ni approved for 2014 from NP PAC RIKEN

24 How to measure:

25 Experimental Setup for g-ray detection with DALI2+ Pb or Au Target 70,72,7X* Ni 70,72,7X* Ni ZDS, Beam DALI 2 NaI E g =10MeV, m g =1) *SAMURAI Hector + LaBr 3 :Ce (e =1-2%) Fep

26 LaBr in Forward Direction Dali2 LaBr Dali2 In Backward direction LaBr

27 With Shogun will be possible to exam the Ni chain and astrophysics impact of PDR n capture Rate <No PDR> and same GDR Parmeters as Model n capture Rate <With PDR> BU RIKEN RIKEN Or DALI2+SAMURAI Ni Ni Isotopes Data From Litvinova at al. NPA 823(2009)26 RQTBA n-capture rates (calc for Ni-chain) relevant for r-process show modest sensitive to low lying dipole strength

28 mb W(theta) [1/sr] 20 Coulomb excitation g-ray Angular Distribution 70,72, 74 on Pb target Expecting with Shogun =SUPER-Sunflower We would expect to measure angular distribution Ni, 68 Ni, 78 Ni photoabsorption 58Ni 68Ni 78Ni Energy (MeV) We would expect To have resolution with Shogun after ADD Back around 350keV (best 300keV)

29 DC DC+ ADD-BACK e FEP =17% FWHM=340keV SHOGUN 930 detectors Ni@230 AMeV on 0.5g/cm^2 Au E g =10MeV. Pieter Doornenbal «Comparable» to Full 4 AGATA@GSI

30 «Cases for 2014 PAC»

31 Most probable Proposal 2014 to be submitted With Zn Beam and Dali2 + 8LaBr 3 :Ce To arrive at 52,54 Ca

32 DALI2+SAMURAI IVGDR 1.E+02 1.E+01 Next Candidate nearby 68 Ni could be Iron 66 Fe, 68 Fe with N=40 and A=68 Expected structure below threshold AND fragmentation of PDR IV Strength 64 Fe (SKI2 ) OR 1.E+00 1.E-01 1.E n Possible with standard BaF+LaBr setups Energy [MeV] 66 Fe, 68 Fe Possible to see fine Structure with Shogun Resolution. Doppler Correction and efficiency IV Strength 66 Fe (SKI2 ) IV Strength 68 Fe (SKI2 ) FWHM=200keV

33 Comparison of Methods and arrays 70,72 Ni 74 Ni 54,56 Ca, 76 Ni 78 Ni?? 2014 PAC

34 «Cases for PAC»

35 Search for pygmy in deformed 100 Zr OPEN QUESTION: Deformation hinders the dipole strength BUT low-lying E1 strength increases with the neutron number D. Pena Arteaga, E. Khan, and P. Ring PRC 79, (2009) 100 Zr To disentangle the PDR finestructure good DOPPLER correction is needed RQRPA highly deformed with beta=0.4 calculations done by Daniel Pena Arteaga ipno.in2p3.fr Orsay

36 Other possible measurements in deformed 10X Zr: PDR properties and lower lying states 102 Zr 102 Zr

37 S [e 2 fm 2 /MeV] Fragmentation of the strength in 26 Ne Systematic E1 Strength predicted by QRRPA calculations (for deformed Ne nuclei) 1.2 Virtual Photon Breakup 85AMeV RIKEN Needs confirmation, continue And additional information With Photon scattering PDR 28 Ne 0 0? PDR 26 Ne 24 Ne? Ne 20 Ne Figure 1: Reconstructed excitation energy spectra from the Coulomb break up measurement [10] of the dipole strength distributions for 26 Ne in function of the gamma ray energy after substraction of background and E2 contributions. Cao L.-G. and Ma Z.-Y. Phys. Rev. C 71, (2005) E* [MeV] J. Gibelin et al., Phys. Rev. Lett. 101, (2008). B(E1) = e 2 fm 2 or % of TRK sum 9 MeV

38 RESUME Great perspectives with SUNFLOWER 1. Ni chain, ( 74 Ni) PDR properties, neutron radius 2. Ca chain (-> 52,54 Ca with 70 Zn Beam And SHOGUN!) 2014 PAC 3. Zr chain, ( 10X Zr) PDR in deformed nuclei 4. Fe chain, PDR nearby Ni ( 66,8 Fe 68 Ni n=40,a=68) 5. Ne chain deformed light nucleus (complem. to PhotonBreakup) 6. Sn chain isoscalar, chain ( 24,.. O) mass region 7. Combination with PhotonBreakup! 8. Different probes and E beams to study nuclear contributions and IV, IS part OPEN QUESTIONS -Level of collectivity? -How (collective) properties change with n? -How isospin changes mean field? -In exotic nuclei: PDR strength also below neutron threshold, or varies with threshold? -No High resolution measurements available -Various nuclei and mass regions -Effect of deformation? -Proton Pygmy? -astrophysical impact

39 The pygmy resonance in medium-mass nuclei ありがとう Thank You