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Problems and Ideas at the Dawn of Three-Body Force Effects in the Shell Model. Takaharu Otsuka University of Tokyo / MSU. ECT* workshop “Three-Nucleon Forces in Vacuum and in the medium” Trento, Italy July 11 (11-15), 20 11. Outline. 1. Monopole problem in the shell model. - PowerPoint PPT Presentation
Citation preview
Problems and Ideasat the Dawn of
Three-Body Force Effects in the Shell Model
Takaharu OtsukaUniversity of Tokyo / MSU
午前 6:12
ECT* workshop “Three-Nucleon Forces in Vacuum and in the medium”Trento, Italy
July 11 (11-15), 2011
Outline
1. Monopole problem in the shell model
2. Shell evolution in exotic nuclei
3. Solution by three-body force
Introduction to talks byJ. Holt, A. Schwenk and T. Suzuki
Spectra of Ca isotopes calculated by mostupdated NN interaction microscopically obtained
By Y. Tsunoda and N. Tsunoda
N3LO
Vlow-k with =2.0 fm-1
2nd and 3rd order Q-box
4hw and 6hw
s.p.e. used
PresentGXPH1A
KB3G
GXPF1AKB3G
for comparison
Two-body matrix elements (TBME) may be calculatedto a rather good accuracy
40Ca core is not very stable yet -> 0+ energy lowered
48Ca
• Monopole component of the NN interaction
Averaged over possible orientations
As N or Z is changed to a large extent in exotic nuclei, the shell structure is changed (evolved) by
Strasbourg group made a major contribution in initiating systematic use of the monopole interaction. (Poves and Zuker, Phys. Rep. 70, 235 (1981))
<nj’ > can be ~ 10 in exotic nuclei -> effect quite relevant to neutron-rich exotic nuclei
nj’ : # of particles in j’Linearity: Shift
T=1 monopole interactions in the pf shell
j = j’ j = j’
Tensor force (+exchange)
G-matrix (H.-Jensen)
GXPF1A
What’s this ?
Basic scale ~ 1/10 of T=0
Repulsive corrections to G-matrix
T=1 monopole interactions in the sd shell
SDPF-M (~USD) G-matrix
(H.-Jensen)
Tensor force (+exchange)
j = j’ j = j’
Basic scale ~ 1/10 of T=0
Repulsive corrections to G-matrix
T=0 monopole interaction
The correction is opposite !
T=0 monopole interactions in the pf shell
GXPF1A
G-matrix (H.-Jensen)
Tensor force (+exchange)
f-f p-p f-p
“Local pattern” tensor force
T=0 monopole interactions in the pf shell
GXPF1Ashell-model int.
G-matrix (H.-Jensen)
Tensor force (+exchange)
Tensor component
is subtracted
Correction isattractive
Outline
1. Monopole problem in the shell model
2. Shell evolution in exotic nuclei
3. Solution by three-body force
Treatment of tensor force by V low k and Q box (3rd order)
Monopole component of tensor interactions in pf shell
short-range correlationby V low k
in-medium correctionwith intermediate states(> 10 hw, 3rd order)
Bare (AV8’)
only for comparison
Systematic description of monopole properties of exotic nuclei can be obtained by an extremely simple interaction as
Parameters are fixed for all nuclei
monopole component of
tensor force in nuclear
medium monopole component of
tensor force in free space
almost equal ?
Shell evolutiondue to proton-neutron tensor + central forces
Changes of single-particle properties due to these nuclear forces
ls splitting smaller
exotic nucleus with neutron skin
proton
neutron
d/dr
stable nucleus
T=1 NN interaction more relevant to ls splitting change
From RIA Physics White Paper
Neutron single-particle energies at N=20 for Z=8~20
Z
8 14Z
16 20
These single-particleenergies are “normal”
f7/2-p3/2 2~3 MeV N=20 gap ~ 6 MeV
energ
y (
MeV
)
d5/2 s1/2 d3/2
16
20
solid line : full VMU (central + tensor)
dashed line : central only
p3/2 low
Tensor force makeschanges more dramatic.
PRL 104, 012501 (2010)more exotic
Increase of 2+ excitationenergy
Neutron number
2+
level (M
eV
)
Outline
1. Monopole problem in the shell model
2. Shell evolution in exotic nuclei
3. Solution by three-body force
Pro
ton
nu
mb
er
Neutron number
Nuclear Chart- Left Lower Part -
Why is the drip line of
Oxygen so near ?
Single-Particle Energy for Oxygen isotopes
Utsuno, O., Mizusaki, Honma, Phys. Rev. C 60, 054315 (1999)
G-matrix+ core-pol. : Kuo, Brown
SDPF-M
- G-matrix + fit -
V low-k : Bogner, Schwenk, Kuo
trend
trend
by microscopic eff. int. by phenomenological eff. int.
USD-B Brown and Richter, Phys. Rev. C 74, 034315 (2006)
What is the origin of
the repulsive modification of
T=1 monopole matrix elements ?
A solution within bare 2-body interaction is very unlikely
(considering efforts made so far) Zuker, Phys. Rev. Lett. 90, 042502 (2003)
3-body interaction
The same puzzle as in the pf shell
The clue : Fujita-Miyazawa 3N mechanism-hole excitation)
particle m=1232 MeV S=3/2, I=3/2
N N N
Miyazawa, 2007
Renormalization of NN interaction due to excitation in the intermediate state
T=1attraction
between NNeffectively
Modification tobare NN interaction(for NN scattering)
Pauli blocking effect on the renormalization of single-particle energy
Pauli blocking effect on the renormalization of single-particle energy
Pauli ForbiddenThe effect is
suppressed
m
m
m’ m’
Renormalization of single particle energy
due to -hole excitation more binding
(attractive)
m
m
m’
singleparticle states
Another valenceparticle in state m’
Pauli forbidden(from previous page) This Pauli effect is
included automaticallyby the exchange term.
m
mm’
m’
m
m’ m’
m
Inclusion of Pauli blocking
Most important message with Fujita-Miyazawa 3NFMost important message with Fujita-Miyazawa 3NF
+
Renormalizationof single particle
energy
m
m
m’
same
Monopole part ofFujita-Miyazawa3-body force
Pauli blockingm
mm’
m’
Effective monopole repulsive interaction
(i) -hole excitation in a conventional way
-hole dominantrole in determiningoxygen drip line
(ii) EFT with
(iii) EFT incl. contact terms (N2LO)
-> J.Holt, A. Schwenk, T. Suzuki
Ground-state energies of oxygen isotopes
Drip line
NN force + 3N-induced NN force (Fujita-Miyazawa force)
O, Suzuki, Holt, O, Schwenk, Akaishi, PRL 105 (2010)
(Effective) two-body interaction
constant change ofsingle-particle energy
If the origin is“forgotten”,
This is what happenedin “microscopic theories”,leading to wrong drip line.
N N
NN
N
NN
N
or
What was wrong with “microscopic theories” ?
Observed in NN scattering
presentpicture
For neutron matter : states below Fermi level
attractive
repulsivek
k
k
k
Brown and Green, Nucl.Phys. A137, 1 (1969Fritsch, Kaiser and Weise, Nucl. Phys. A750, 259 (2005); Tolos, Friman and Schwenk, Nucl.Phys. A806}, 105 (2008); Hebeler and Schwenk, arXiv:0911.0483 [nucl-th]
For valence neutrons: states outside the core
Attractive (single-particle energy renormalization)
repulsive
(valence neutron interaction)
Major monopole forces are due to
+V
=1 fm
Quick Summary More from J. Holt, A. Schwenk and T. Suzuki
+
FM 3NF
basic binding (T=0),repulsive (T=1) except for j=j’
variation ofshell structure
limit of existence,shell structure at far stability
Casablanca mechanism
RickVictor
This love is reduced by the presence of Rick
This love is reduced by the presence of Victor
repulsion
Love = attractive force*
*This equation hasno proof.
E N D
The central force is modeled by a Gaussian function
V = V0 exp( -(r/) 2) (S,T dependences)
with V0 = -166 MeV, =1.0 fm,
(S,T) factor (0,0) (1,0) (0,1) (1,1) -------------------------------------------------- relative strength 1 1 0.6 -0.8
Can we explain the difference between f-f/p-p and f-p ?
Spin-orbit splitting
Eigenvalues of HO potential
Magic numbers
Mayer and Jensen (1949)126
8
20
28
50
82
2
5h
4h
3h
2h
1h
density saturation + short-range NN interaction + spin-orbit splitting
Mayer-Jensen’s magic number
with rather constant gaps (except for gradual A dependence)
robust feature -> nuclear forces not included in the above can change it
-> tensor force
Magic numbers may change due to spin-isospin nuclear forces
Tensor force produces unique and sizable effect
Tensor and central forces -> Weinberg-type model
Brief history on our studies on tensor force
VT = (2) Y(2 Z(r)
contributes only to S=1
states
relative motion
meson (~ +) : minor (~1/4) cancellation
meson : primary source
Ref: Osterfeld, Rev. Mod. Phys. 64, 491 (92)
Tensor Interaction by pion exchange
Yukawa
How does the tensor force work ?
Spin of each nucleon is parallel, because the total spin must be S=1
The potential has the following dependence on the angle with respect to the total spin S.
V ~ Y2,0 ~ 1 – 3
cos2
attraction=0
repulsion=/2
S
relativecoordinate
Monopole effects due to the tensor force
- An intuitive picture -
wave function of relative motion
large relative momentum small relative momentum
attractive repulsive
spin of nucleon
TO et al., Phys. Rev. Lett. 95, 232502 (2005)j> = l + ½, j< = l – ½
wave function when two nucleons interact
k1k2
k1k2
- approx. by linear motion -
k = k1 – k2 , K = k1 + k2
large relativemomentum k
strong damping
wave functionof relative coordinate
k1k2
wave functionof relative coordinate
small relativemomentum k
loose damping
k1k2
j> = l + ½
j< = l – ½
j’<
proton
neutron
j’>
General rule of monopole interaction
of the tensor force
Identity for tensor monopole interaction
(2j> +1) vm,T + (2j< +1) vm,T = 0( j’ j>) ( j’ j<)
vm,T : monopole strength for isospin T
TO. et al., Phys. Rev. Lett. 95, 232502 (2005)
The central force is modeled by a Gaussian function
V = V0 exp( -(r/) 2) (S,T dependences)
with V0 = -166 MeV, =1.0 fm,
(S,T) factor (0,0) (1,0) (0,1) (1,1) -------------------------------------------------- relative strength 1 1 0.6 -0.8
Can we explain the difference between f-f/p-p and f-p ?
GXPF1
G-matrix (H.-Jensen)
Central (Gaussian)- Reflecting
radial overlap -
Tensor force (+exchange)
T=0 monopole interactions in the pf shell
f-f p-p f-p
S. Weinberg, PLB 251, 288 (1990)
Tensor force is explicit
Central force:strongly renormalized
finite range(Gaussian)
In nuclei
+ exchange
Similarity to Chiral Perturbation of QCD
Central part changes as the cut-off changes
T=0 T=1
j-j’
Mon
opol
e in
t. (M
eV)
Tensor (reminder)
from Dickhoff
Rat
io to
naï
ve s
ingl
e-pa
rtic
le m
odel
Measured spectroscopic factors
short-range +in-mediumcorrections
Tensor force remains almost unchanged !
Higher order effectsdue to the tensor forceyield renormalization of central forces.
Multipole component of tensor forces- diagonal matrix elements -
Test by experiments
Z =51 (= 50 + 1) isotopes
No mean field theory, (Skyrme, Gogny, RMF) explained this before.
An example with 51Sb isotopes with VMU interaction
tensor force in VMU (splitting increased by ~ 2 MeV)
change driven by neutrons in 1h11/2
g7/2
Consistent with recent experiment
One of the Day 1 experiments at RIBF by Nakamura et al.
- Position of p3/2
FromGrawe, EPJA25,357
g9/2 occupied
E (
MeV
)
N
Central Gaussian+ Tensor
solid line: full VMU effect
dotted line: central only
Crossing hereis consistentwith exp. onCu isotopes
Proton single-particles levels of Ni isotopes
shaded area : effect of tensor force
solid line : full VMU (central + tensor)
dashed line : central only
shaded area : effect of tensor force
Shell structure of a key nucleus 100Sn
Exp. d5/2 and g7/2 should be closeSeweryniak et al. Phys. Rev. Lett. 99, 022504 (2007) Gryzywacz et al.
Zr Sn
Potential Energy Surface
s1/2
Z=28 gap is reduced alsoproton
neutronf7/2d3/2
d5/2
full
Tensor force removedfrom cross-shell interaction
Strong oblateDeformation ?
Otsuka, Suzuki and Utsuno,Nucl. Phys. A805, 127c (2008)
exp.
4214Si28
42Si
Other calculationsshow a variety of shapes. 42Si: B. Bastin, S. Grévy et al.,
PRL 99 (2007) 022503
Si isotopesSM calc. by Utsuno et al.
Spectroscopic factors obtained by (e,e’p)
on 48Ca and the tensor force
Collaboration with Utsuno and Suzuki
Spectroscopic factor for 1p removal from 48Ca
• d5/2 deep hole state
– More fragmentation
• Distribution of strength
– quenching factor 0.7 is needed (as usual).
– Agreement between
experiment and theory for both position and strength (e,e’p): Kramer et al., NP A679, 267 (2001)
Same interaction as theone for 42Si
What happens, if the tensor force is taken away ?
no tensor in the cross shell part
s1/2
d3/2
d5/2
with full tensor force
Summary
2. The tensor force remain ~unchanged by the treatments of short-range correlations and in-medium correction. This feature is very unique.
3. (e, e’p) data on 48Ca suggests the importance of the tensor force, which is consistent with exotic feature of 42Si.
Direct reactions with RI beam should play important roles in exploring structure of exotic nuclei driven by nuclear forces.
1. Changes of shell structure and magic numbers in exotic nuclei are a good probe to see effects of nuclear forces. Such changes are largely due to tensor force, as have been described by VMU. Transfer reactions have made important contributions.
4. Fujita-Miyazawa 3N force can be the next subject for the shell evolution.
Summary1. Monopole interactions : effects magnified in neutron-rich nuclei
2. Tensor force combined with central force : a unified description particularly for proton-neutron monopole correlation. -> N=20 Island of inversion, 42Si, 78 Ni, 100Sn, Sb, 132Sn, Z=64,…
Tensor force in nuclear medium is very similar to the bare one.This central force may be a challenge for microscopic theories.
3. Fujita-Miyazawa 3-body force produces repulsive effective interaction between valence neutrons in general.
The spacings between neutron single-particle levels can become wider as N increases, and new magic numbers may arise.Examples are shown for O and Ca isotopes with visible effects.
<--> shell quenching 4. Structure change on top of the shell evolution -> diagonalization with super computer
Collaborators
T. Suzuki Nihon U.M. Honma AizuY. Utsuno JAEAN. Tsunoda TokyoK. Tsukiyama Tokyo M. H.-Jensen Oslo
A. Schwenk DarmstadtJ. Holt ORNLK. Akaishi RIKEN
E N D
SPE : GXPF1 f7:-8.62 f5: -1.38 p3: -5.68 p1: -4.14
Ca ground-state energy cont’d
Ca 2+ level systematics
2+ of 48Ca rises by 3N becomes about right by using GXPF1A SPE
N=32, 34 higher 2+ levels
Spin quenching factor 0.8
8-13MeV
GXPF1
spe : GXPF1
48Ca M1 excitation 10
Dominant monopole forces are due to
+V
=1 fm
Summary-2
+
FM 3NF
basic binding variation ofshell structure
limit of existence
古典力学での三体問題と三体力
(有効三体力)
MG
GM
EG
GE
EM
ME
G
G
M
M
E
E
r
mGm
r
mGm
r
mGm
m
P
m
P
m
PH
222
222
),,( GME rrrV
ここでの三体力は、二体力+超多体問題を回避するための“有効”相互作用 .
正真正銘の三体力は存在するか?
GPS の位置をこの方程式を数値的に解いても正確には求まらない。 GPS の役割を果たさない!
それは地球が変形するから(もちろん相対論効果もあるが)
酒井(英)氏より拝借
Ground-state energies of oxygen isotopes
Drip line
NN force + 3N-induced NN force (Fujita-Miyazawa force)
Collaborators
T. Suzuki Nihon U.M. Honma AizuY. Utsuno JAEAN. Tsunoda TokyoK. Tsukiyama Tokyo M. H.-Jensen Oslo
A. Schwenk TRIUMF/DarmstadtJ. Holt ORNLK. Akaishi RIKEN