giant and pygmy resonance in relativistic approach
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Giant and Pygmy Resonance in Relativistic Approach. The Sixth China-Japan Joint Nuclear Physics May 16-20, 2006 Shanghai Zhongyu Ma China Institute of Atomic Energy, Beijing Collaborators: Ligang Cao, Baoqiu Chen, Jun Liang. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
Giant and Pygmy Resonance in Relativistic Approach
The Sixth China-Japan Joint Nuclear PhysicsThe Sixth China-Japan Joint Nuclear Physics
May 16-20, 2006
Shanghai
Zhongyu Ma
China Institute of Atomic Energy, Beijing
Collaborators: Ligang Cao, Baoqiu Chen, Jun Liang
Introduction
Nucleus moving away from the valley of -stability
diffuse neutron: neutron skin, hallo structure,
new magic numbers, new modes of excitations, etc.
Significant interest on low-energy
excited states
GDR (Coulomb excitations)
restoring force proportional to the symmetry energy
Pygmy resonance
Loosely bound neutron coherently oscillate
against the p-n core
neutron density distribution, neutron radius,
skin et al. density dependence of symmetry energy
Astrophysical implications
Fully Consistent RRPA
RRPA -- Consistent in sense:
ph residual interaction determined from the same Lagrangian for g.s. RRPA polarization operator
i=,, i=1, , 3 for , , , respectively
consistent to RMF no sea approx.
Include both ph pairs and h pairs
Z. Y. Ma, et al., Nucl. Phys. A703(2002)222
RRPA TDRMF at small amplitude limit
TDRMF at each time no sea approximation is calculated in a stable complete set basis P.Ring et al., Nucl. Phys. A694(2001)249
2 3 30 1 2 0( , ; , '; ) ( , ; , ; ) ( , ; ) ( , ; , '; )i
i i ii
Q Q E g d k d k Q E D E Q E 1 1 2 2k k k k k k k k
Fig: ISGMR NL1,NL3,TM1,NLSH
Z.Y. Ma, et al., Nucl. Phys. A686(2001)173
M.E. of vector fields coupling h and ph----Largely reduced due to Dirac str.
Cancellation of the & fields --- not take place, Large M.E. coupling h and ph exist
Treatment of the continuum
Resonant states in the continuum
Metastable states in
the centrifugal & Coulomb Barrier
Discretization of the continuum
Expansion on Harmonic Oscillator basis
Box approximation: set a wall at a large distance
Exact treatment of the continuum
Set up a proper boundary condition
Single particle resonance with energy and width
Green’s function method
Scattering phase shift
Centrifugal & Coulomb
Nuclear Pot.
Total
Scattering phase shift
Boundary conditions:
Normalized by
phase shift: = /2 resonant state
For proton, Dirac Coulomb functions have to be solved
for ~1 Z large large diff. from norn Coulomb wf
Cao & Ma PRC66(02)024311
W. Grainer “Rel. Quantum Mach.”
( ) [ ( ) tan ( )], forl lG kr A j kr n kr r R
†( , ) ( ', ) ( ')E r E r dr E E
1cos
2
M EA
k
Example of resonance states
More resonant states
for p than those for n
due to the Coulomb
barrier
-10 -5 0 5 10
-80
-60
-40
-20
0
20
3p3/2
3p1/2
2g9/2
Vp(r)+V
c(r)
Vp(r)
Vn(r)
N P 1j15/2
1i11/2
1h9/2
1i11/2
1i13/21h
9/2 2f7/2
2f5/2
1i13/2
2f5/2
3s1/22d3/2
2d5/21g7/2
1g9/22p
1/2
2p3/2 1f
5/21f7/2
1g9/2
2p1/2
2p3/2
1f5/2
1f7/2
2s1/2
1d3/2
1d5/2
1p1/2
1p3/2
1s1/2
2s1/2
1d3/2
1d5/2
1p1/21p3/2
1s1/2
Ene
rgy(
MeV
)
R(fm)
120Sn
Resonant continuum in pairing correlations
Pairing correlations play a crucial role in MF models for open shell
HF+BCS and RMF+BCS simple
successful in nuclei when F not close to the continuum
HFB and RHB important in nuclei near the drip-line
HF eq. + gap eq. are solved simultaneously
states in continuum are discretized in both methods
Resonant states : HFB eq. are solved with exact boundary conditions
Grasso, Sandulescu, Nguyen, PRC64(2001)064321
Discretization of the continuum overestimates pairing corr.
Effect of the continuum on pairing --- mainly by a few resonant
states in the continuum
RMF+BCS with resonant states including widths
BCS with the continuum
Gap equation :
Nucleon densities:
Continuum level density
Pairing correlation energy
BCS are good in the
vicinity of the stable
line.
Width effects are
large for nuclei far
from the stability line.
60 70 80 900
1
2
3
4
5
6
ER
MF-E
RM
F+
BC
S(M
eV
)
A
RMF+BCS RMF+BCSR RMF+BCSRW
Ni-isotopes
N=50
Cao, Ma , Eur. Phys. J. A 22 (2004)189
Quasi-particle RRPA
2
0
2 1
(4 )( , ; , '; ) ( )
2 1 ( ) ( )
( ( ) ) (1 )
L L L Lj jR
L
P Q P QP Q k k E A
L E E E i E E E i
A u v v u
Response function
Unperturbed polarization operator
BCS occupation prob.
Outside the pairing active space
Positive unoccu. states
occu. states
Negative states
2v 22 2 21 , n nu v E
2 2, 0, 1nE v u
2 2, 1, 0nE v u
2 2, 0, 1nE v u
1( , ; , '; ) Im ( , ; , '; )RR Q Q E Q Q E
k k k k
Ni-isotopes
64 68 72 76 80 84 88 92 96 100
3.5
4.0
4.5
5.0Ni-isotopes
R(f
m)
A
neutron proton
64 68 72 76 80 84 88 92 96 100-8.8
-8.4
-8.0
-7.6
-7.2
-6.8
EB/A
(MeV
)
A
Theory Exp.
64 68 72 76 80 84 88 92 96 1000.0
0.2
0.4
0.6
0.8
1.0
1.2
Ni-Isotopes
Rn-R
p(fm
)
A
Extended RMF+BCS
s.p. resonant states
2d5/2,2d3/2,1g7/2,2f7/2,1h11/2,
G=20.5/A MeV
Cao, Ma, Modern Phys. Lett. A19(2004)2845
IVGDR Ni-isotopes
0
2
4 70Ni
C
84Ni
0
2
4
72Ni
86Ni
0
2
4
74Ni88Ni
(e2 fm
2 MeV
-1)
IVG
DR
0
2
4 76Ni
Re
spo
nse
Fu
nct
ion 90Ni
0
2
4 78Ni
C
92Ni
0
2
4
E(MeV)E(MeV)
80Ni
94Ni
0 5 10 15 20 25 300
2
4
82Ni
0 5 10 15 20 25 30
96Ni
58Ni – 64Ni are stable
vibration of p-n
Ni-isotopes A=70~96
The response functions
of IVGDR in QRRPA
Loosely bound neutron coherently oscillate against the p-n core
EH ~ 16 MeV
low-lying dipole <10 MeV
IVGDR in Ni-isotopes
0.2 0.4 0.6 0.8 1.05
6
7
8
9
10E
L(MeV
)
rn-r
p
68 72 76 80 84 88 92 96 1004
6
8
10
EL(M
eV)
A
68 72 76 80 84 88 92 96 10014
16
18
20
EH(M
eV)
m1/m
0 GDR
E(A)=31.2A-1/3+20.6A-1/6
68 72 76 80 84 88 92 965
10
15
20
25
30
35
Per
cent
age(
%)
Cao, Ma, Modern Phys. Lett. A19(2004)2845
GDR
restoring force proportional to the symmetry energy
Linear dep. on the neutron skin
Experiments on GDR
Gibelin and Beaumel (Orsay), exp. at RIKEN
inelastic scattering of 26Ne + 208Pb
60 MeV/u 26Ne secondary beam
Dominated by Coulomb excitations
selective for E1 transitions.
Thesis of J. Gibelin IPNO-T-05-11
Future work:
28Ne + 208Pb
Theoretical investigation – practical significance0 5 10 15
10-6
10-5
10-4
10-3
10-2
10-1
Den
sity
(fm
-3)
r(fm)
p(26Ne)
n(26Ne)
p(28Ne)
n(28Ne)
Cao, Ma, PRC71(05)034305
Properties of 26,28Ne
Extended RMF+BCS with NL3
GQR check the validity of spherical assumption
26Ne, 28Ne IVGDR
0 5 10 15 20 25 30 350.0
0.5
1.0
R(e
2 fm2 M
eV
-1)I
VG
DR RRPA
QRRPA
26Ne
Cao, Ma, PRC71(05)034305
0 5 10 15 20 25 30 350.0
0.5
1.0
1.5
R(e
2 fm2 M
eV-1
)IV
GD
RE(MeV)
RRPA QRRPA
28Ne
Sum rule
Low-lying GDR in 26Ne exhaust about 4.9% of TRK sum rule
28Ne 5.8%
Comparisons of Low-lying dipole state in 26Ne
Authors Methods Shape Result
Elias(Orsay) SHF+BCS+ spherical 11.7 not coll.
QRPA(RF)
Cao, Ma(CIAE) RMF+BCS(R.) spherical 8.4(5%) coll.
PRC71(2005)034305 +QRRPA(RF)
Peru(CEA) def. HFB(Gogny) Spherical 10.7 coll.
+QRPA(Matrix)
Ring(TUM) def. RHB +QRRPA Deformed 7.9 9.3 less coll.
(Matrix)
Exp.(Gibelin,Beaumel) measure ? ~9(5%)
IPNO-T-05-11
Preliminary
Symmetry Energy and GDR
Restoring force of GDR
Symmetry energy in NM
All parameters give very good
description of g.s. properties,
NM saturations
Centroid energy of GDR
Ecen=m1/m0
Linear dep on the symmetry
energy at saturation energy
May give constraint:
33 MeV< asym(0)<37 MeV
32 33 34 35 36 37 38 39 40 41 42 4310
11
12
13
14
15
16
17
18
19
90Zr
144Sm
E(M
eV)
IVG
DR
S (0) (MeV)
208Pb
NLSHNL3 NL-BA
NLENLZ2
NLVT
Density dep. of symmetry energy
Non linear - coupling
Todd, Pickarewicz, PRC67(03)
Modify the poorly known density dep. of symmetry energy
Without changing the agreement with existing NM, g.s. properties
Softening of the symmetry energy
NL3 B/A=16.24MeV
asym=37.3 MeV
0=.148fm-3(kF=1.3fm-1)
K=272 MeV
asym=25.67 MeV at =.1fm-3(kF=1.15fm-1)
int ( )v g g L=
0.00 0.05 0.10 0.15 0.200
10
20
30
40
50
60
asy
m (
Me
V)
(fm-3)
V=0.0
V=0.015
V=0.025
Ground state properties in 132Sn
v B/A(MeV)
rp(fm) rn(fm) rn-rp 0 asym(MeV) asym(=0.
1)
0 8.320 4.643 4.989 0.346 0.148 37.34 25.68
0.015 8.340 4.647 4.949 0.302 0.148 34.05 25.68
0.025 8.346 4.653 4.926 0.273 0.148 32.41 25.68
Exp. 8.355
B/A, rp slightly changed
asym softened
rn-rp becomes small
3.0 3.5 4.0 4.5 5.0 5.5 6.0
-60
-50
-40
-30
-20
-10
0
n (M
eV)
Neutron rms radius (fm)
V=0.0
V=0.025
NL3
132Sn
Pygmy Resonance & Symmetry Energy
20 21 22 23 24 25 26 27 287.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
E(M
eV
) P
DR
S () (MeV) (at =0.1 fm-3)
132Sn
0 5 10 15 20 25 300
2
4
6
R (
e2 fm
4 Me
V-1)
IVG
DR
E (MeV)
v=0.025
v=0.015
v=0.0
132Sn
NL3
Epeak(Pygmy)=8.0 MeV above one n separation energy
Epeak(GDR)= 13.8, 14.0, 14.2 MeV Adrich et al. PRL95(05)132501
GDR : peak energy is shifted dep. on the symmetry energy at 0
Pygmy resonance is kept unchanged at 8.0 MeV
It may set up a constraint on the density dep. of symmetry energy
GSI
Summary
Theoretical investigations on Pygmy resonance in quasi-particle RPA
non-relativistic QRPA
relativistic approaches QRRPA
Pairing correlation is important, coupling to the continuum
Extended RMF+BCS
the s.p. resonance in the continuum including widths
GDR -- restoring force is proportional to the symmetry energy
systematic study
33 MeV < asym(0) < 37 MeV
New excitation modes in exotic nuclei
Pygmy modes are related to neutron skin and density dependence of
symmetry energy
Thanks Thanks