symmetry energy from pigmy dipole and giant resonances

OUTLINE OUTLINE

MotivationMotivation

Experiment description Experiment description

Results Results

Comparison with theory Comparison with theory

Conclusions and perspectives Conclusions and perspectives

Symmetry Energy from Pigmy Dipole and Giant Resonances

F. CameraUniversity of Milano and INFN Milano

http://www-linux.gsi.de/~wolle/EB_at_GSI/ICONS/rising-big.gif

two Phononcouplings

2+3-

GDR

Richter NPA 731(2004)59

two Phononcouplings

2+3-

GDR

Stable Nuclei Photoabsorption

two Phononcouplings

2+3-

GDR

Stable nuclei Photoabsorption

Neutron rich nuclei

Virtual photon scattering Neutron breakup

Why the Pygmy Resonance is important ?Why the Pygmy Resonance is important ?

• Is it collective ?• How collective properties change with neutron number ?• How deformation acts ?



• How PDR affects the r-process nucleosynthesys ?

“Giant Resonances are of paramount importance for nuclear astrophysics. Often, relevant reaction rates under astrophysical conditions are dominated by giant resonances contributions frequently in unstable nuclei. For instance neutron rich nuclei with loosely bound valence neutrons may exhibit very strong (g,n) strength components near particle threshold and thus, in turn, enhanced neutron capture rates.”NUPECC long range Plan 2004



• How PDR affects the r-process nucleosynthesys

“Giant Resonances are of paramount importance for nuclear astrophysics. Often, relevant reaction rates under astrophysical conditions are dominated by giant resonances contributions frequently in unstable nuclei. For instance neutron rich nuclei with loosely bound valence neutrons may exhibit very strong (g,n) strength components near particle threshold and thus, in turn, enhanced neutron capture rates.”NUPECC long range Plan 2004

• As in a hydrodynamic approach the excitation energy of IVGDR depends on a combination of volume and surface symmetry energy, can PDR provide information on L and neutron skin ?

“we suggest that the electromagnetic excitation of both the pygmy and giant dipole resonances will continue to provide powerful constraints on the density dependence of the symmetry energy” Piekarewicz PRC83(2011)034319

“We can conclude that our more general analysis of the extraction of the slope parameter L from the PDR is able to provide a firm result”A.Carbone et al. PRC81(2010)041301

Virtual photon breakup

Riken, GSI experiments

Virtual photon scattering

MSU, RISING experiments

PDR in neutron rich nuclei

Light nuclei

Leistenschneider et al. Phys. Rev. Lett. 86, 5442 (2001).E. Tryggestad et al. Phys. Lett. B 541, 52 (2002).J. Gibelin et al PRL 101, 212503 (2008)

Medium Mass nuclei

+this work on 68Ni

P. Adrich et al. Phys. Rev. Lett. 95, 132501 (2005).

Lots of work but few data available

RMF

68Ni~10 MeV7%

D. Vretnar et al. NPA 692(2001)496 G. Colo private communications

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25 30 35 40

Energy (MeV)

mb

RPA

68Ni~10 MeV3-8%

J. Liang et al., PRC75(2007)

fRPA: 7-8%:

Theoretical predictions before the experiments

Different approaches give similar predictions in terms of collectivity, strength and line-shape of the pygmy resonance

SearchSearch forfor pygmypygmy strengthstrength in in 6868Ni in Ni in theorytheory

Virtual photon scattering technique

• Peripheral heavy-ion collision on a high Z target at relativistic energies

• Virtual photon excitation and decay

• Relativistic Coulomb excitation has very high selectivity for dipole excitation

b > bmin

Virtual photon

q << qmax

g emission

T.Aumann et al EPJ 26(2005)441

PbO 20816

600 MeV/u 68Ni + 197Au

400 MeV/u 68Ni + 197Au

20)(

)(

GQR

GDR

197Au(68Ni,68Ni*+g)197Au

Maximum excitation energy (adiabatic cut off) ca. E = 18.5 MeV

Virtual photon scattering technique

• Peripheral heavy-ion collision on a high Z target at relativistic energies

• Virtual photon excitation and decay

• Relativistic Coulomb excitation has very high selectivity for dipole excitation

b > bmin

Virtual photon

q << qmax

g emission

600 MeV/u 68Ni + 197Au

400 MeV/u 68Ni + 197Au

197Au(68Ni,68Ni*+g)197Au

Maximum excitation energy (adiabatic cut off) ca. E = 18.5 MeV

Coulex

g

g.s.

Virtual photon excitation and decay of GDR + PYGMY

86Kr @ 900 MeV/u on Be target (4g/cm2) 68Ni

1010 ppspill 86Kr, Spill length 6s, period 10 s

68Ni @ 600 MeV/u on Au target (1g/cm2) cocktail of 104 pps ions Spill length 6s, period 10 s

FRS provides secondary

radioactive ion beams

FRS provides secondary

radioactive ion beams

2g/cm2

Au

CATEPosition sensitiveE-DE Telescope

for beam identificationafter target

High resolution g-spectroscopy at the FRS of GSI


Coulomb excitation of 68Ni @ 600 AMeV

Beam cocktail of 5 isotopes

~ 6 Days of effective beam time~ 400 GB of data recorded

~ 1.108 ‘ good 68Ni events ‘ 0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

35.00%

40.00%

66Co 67Ni 68Ni 69Ni 70Cu

~ 35%

Incoming 68Ni beam

Outgoing 68Ni

DE (Si)

E (

CsI)

68NiGATE

HiglyHigly selective gatesselective gates

•• Large reduction in statisticsLarge reduction in statistics

•• Conditions:Conditions:

• 68Ni-incoming-selection• 68Ni-outgoing-selection• TOF-in prompt• Outgoing angle check• Doppler correction• mg=1• Detector specific (PSA, AddBack)

gg--raysrays spectrumspectrum ofofBaFBaF2 2 detectors detectors

Excess g-ray yield

Emission from target

Folded with Response Functionincluding Doppler correction

Emission from Beam-only GDR, no PDR -

Folded with Response Functionincluding Doppler correction

• High energy g-ray spectra measured in BaF2 detectors evidence a clear excess of g-rays between 10-12 MeV

• Same evidence in HPGe cluster detectors

Ground Ground state state gg decaydecay fromfrom a a GDR GDR state state afterafter a Coulomb a Coulomb excitationexcitation

Beene, Bortignon, Bertulani

The measured g-ray yield is due to the product of 3 terms:

Virtual photon number, photoabsorption, Branching Ratio

TOTAL Virtual Photon Number

1

10

100

1000

0 10 20 30Eg [MeV]

N(Eg,E1)= 2p∫b(n(Eg,E1))db

Integration over W or b

Known from theory


Beene, Bortignon, Bertulani



0

2

4

6

8

10

12

14

16

0 20

Gamma Energy [MeV]

Ph

oto

ab

so

rp

tio

n

cro

ss s

ecti

on

(a

.u.)

GDRPDR

Our final objective

J. R. Beene, G. F. Bertsch, P. F. Bortignon, and R. A. Broglia Phys. Lett.

B 164, 19 (1985)

Thanks to J. Alhassid




20

40

60

80

100

120

140 (g,n)

0.1

1

10

100

1000 VP

VP and Rg

m

b

8 10 12 14 16 18 200.1

1

68

Ni@600 MeV/u GDR

PDR

Total

d/d

E [m

b/M

eV

]

Eg [MeV]

20

40

60

80

100

120

140 (g,n)

0.1

1

10

100

1000 VP

VP and Rg

m

b

8 10 12 14 16 18 200.1

1

68

Ni@600 MeV/u GDR

PDR

Total

d/d

E [m

b/M

eV

]

Eg [MeV]

GDR

PDR )()()(1

)()(1

)(

ggggg

g

g

ggg

g

g

gg

EREEd

dn

E

EEd

dn

E

E

W

W

20

40

60

80

100

120

140 (g,n)

0.1

1

10

100

1000 VP

VP and Rg

mb

8 10 12 14 16 18 200.1

1

68

Ni@600 MeV/u GDR

PDR

Total

d/d

E [m

b/M

eV

]

Eg [MeV]

PDR5%

GDR

RESULT:RESULT: PygmyPygmy dipoledipole resonanceresonance in in 6868Ni Ni

O. Wieland et al., PRL102(2009)092502

Next steps :Next steps :

Deduce L Deduce L Deduce the Neutron radiusDeduce the Neutron radius

Next steps :Next steps :

Deduce L Deduce L Deduce the Neutron radiusDeduce the Neutron radius

Centroid 11 MeV

Width ≈ 2 MeVInstrumental (Doppler Broadening)

Strength = 5 (±1.5) % of the EWSR

B(E1) = 1.2 e2fm2

Correlation between L and the PDR

Several theoretical works have shown that PDR properties can be correlated and provide constraint to the symmetry energy slope

However this approach:

- is not fully accepted - gives predictions which strongly depends on the used nuclear force

we belive that PDR measurements are a valuable tool in the study of symmetry energy and that a correlation between PDR and L exist.

- see talk of X. Roca-Maza


This technique has been previously used but here the approach has been pursued usingdifferent nuclei and different classes of forces (Blue=Skyrme; red=RMF)

A.Carbone et al. PRC81(2010)041301See talk of X. Roca-Maza

Once extracted a value for L it is possible to infer, using the same technique, a value for the neutron skin thickness.


Exp. values fromO. Wieland et al., PRL 102, 092502 (2009); P. Adrich et al .PRL 95, 132501 (2005)A. Klimkiewicz et al., PRC 76, 051603(R) (2007).

TheoryA.Carbone et al. PRC81(2010)041301

B.A. Brown, PRL 85, 5296 (2000);

S. Typel and B.A. Brown, PRC 64, 027302(R) (2001).

R.J. Furnstahl, NPA 706, 85 (2002);

S. Yoshida and H. Sagawa, PRC 69, 024318 (2004).

ExtractExtract the the neutronneutron radiusradius forfor 208208PbPb

The analysis of Klimkiewicz et al. based on 132Sn data gave for 208Pb

Rn-Rp = 0.18 +/- 0.035 for 208Pb

The analysis of Klimkiewicz et al. based on 132Sn data gave for 208Pb

Rn-Rp = 0.18 +/- 0.035 for 208Pb

L(MeV)L(MeV)

Rn-Rp = 0.195 +/- 0.021 fm for 208Pb

Rn-Rp = 0.25 +/- 0.045 fm for 132Sn

Rn-Rp = 0.20 +/- 0.02 fm for 68Ni

Comparison with other ways of constraining L

The used approach to extract Lfrom the measured PDR EWSRproduce a results which iscompatible/comparable to theexperimental results from dataanalysis of heavy-ion collisionsexperiment.

ComparisonComparison withwith heavyheavy ionsions fragmentationfragmentation reactionsreactions

Constraints on the Density dependence of the Symmetry Energy

M.B. Tsang et al. PRL102(2009)122701 + this analysis

Two different analysis and measured quantities give consistentconstraints to the symmetry energy !

This work

S0 = 32.3 1.3 MeV

L = 64.8 15.7 MeV

ConclusionsConclusions + + PerspectivesPerspectives• We have measured the Pygmy Dipole Resonance in 68Ni using the virtual photon

scattering technique

• Combined analysis of our 68Ni PDR data and that of 132Sn have provided a value for L and for DR

• Data from LAND on 68Ni

• We have planned experiments on 70,72Ni and on 64Fe using an array LaBr3:Ce• Experiment planned for 20-24O in Riken (Baba) using an array LaBr3:Ce• Hopefully others

• Theoretical work and data are needed to fix the correlation between PDR and L

RISING

PYGMY

Collaboration

A. Braccoa, G. Benzonia, N. Blasia, S. Brambillaa, F. Cameraa,F.C.L. Crespia, S. Leonia, B. Milliona, R.Nicolinia

O. Wielanda, A. Majb, P. Bednarczykb,c ,J. Gręboszb, M. Kmiecikb, W. Męczyńskib, J. Styczeńb,T. Aumannc,

A. Banuc, T. Beckc, F. Beckerc, L. Caceresc, P. Doornenbalc, H. Emlingc, J. Gerlc, H. Geisselc, M. Gorskac,

O. Kavatsyukc, M. Kavatsyukc, I. Kojouharovc , N. Kurzc,R. Lozevac, N. Saitoc, T. Saitoc, H. Schaffnerc,

H.J. Wollersheimc, J. Jolied, P. Reiterd, N. Warrd , G. de Angelise, A. Gadeae, D. Napolie, S. Lenzif , S. Lunardif ,

D. Balabanskig, G. Lo Biancog, C. Petracheg, A. Saltarellig ,M. Castoldih, A. Zucchiattih, J. Walkeri, A. Bürgerj

and the FRS Collaboration

…

aUniversity of Milan and INFN Section of Milan, Italy

bInstitute of Nuclear Physics, Polish Academy of Sciences, Kraków, Poland

cGSI, Planckstrasse 1, 64291, Darmstadt, Germany

dUniversity of Koeln, Germany

eNational Laboratory of Legnaro, INFN, Italy

fUniversity of Padova and INFN Section of Padova, Italy

gUniversity of Camerino, and INFN Section of Perugia, Italy

hINFN Section of Genova, Italy

iUniversity of Surrey, United Kingdom

jHISKP, University of Bonn, Nußallee 14–16, 53115 Bonn, Germany

Analysis using theory…….A.Carbone, P.F. Bortignon, A. Bracco, F. Camera, G. Colò, O. Wieland(University of Milano and INFN) Phys. Rev. C 81 (2010) 041301(R)

Analysis using theory…….A.Carbone, P.F. Bortignon, A. Bracco, F. Camera, G. Colò, O. Wieland(University of Milano and INFN) Phys. Rev. C 81 (2010) 041301(R)


symmetry energy from pigmy dipole and giant resonances

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