symmetry energy from pigmy dipole and giant resonances
TRANSCRIPT
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
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 ?
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
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
• 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
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
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
Ground Ground state state gg decaydecay fromfrom a a GDR GDR state state afterafter a Coulomb a Coulomb excitationexcitation
The measured g-ray yield is due to the product of 3 terms:
Virtual photon number, photoabsorption, Branching Ratio
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
Correlation between L and the PDR
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.
Correlation between L and the PDR
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)