Transcript T - FB19

FB19 at Bonn, August 31, 2009
Gamow-Teller Strength in the A=4 System
-- Experimental search of GT states excited from
the 4He nucleus, possibly having a narrow width --
A. Tamii
Research Center for Nuclear Physics, Osaka University
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Collaborators
Experiment:
A. Tamii and Y. Fujita
T. Adachi, H. Fujita, K. Fujita, K. Hatanaka, D. Ishikawa,
M. Kato, T. Kawabata, N.T. Khai, H. Matsubara,
H. Okamura, Y.Y. Oo, H. Sakaguchi, Y. Shimbara,
K. Suda, Y. Tameshige and M. Yosoi
Theory:
H. Toki, T. Myo, Y. Ogawa, and E. Hiyama
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Contents
• Motivation
– Narrow GT states and pionic correlation
(G ~ 100 keV)
– GT strength in 4He and delayed supernova
explosion
• Experiment: 4He(3He,t)
• Preliminary Results
• Summary
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Motivation
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Fine Structure of the Gamow-Teller Resonance
GT: DL=0, DS=1, DT=1
transition: 0+ → 1+
Y. Fujita et al., EPJ A 13, 411 (2002)
The GT strength in 58Cu has
been resolved into many
fragmented narrow peaks
with widths of ~ 100 keV.
Similar fragmentation is
commonly found in sd- and
pf- shell nuclei.
↑
Sp
How these
• large fragmentation
• narrow widths
can be explained be theory?
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Pionic Correlation in Nuclei
•
•
A kind of 2p-2h diagram mediated by pion
exchanges are embedded in the ground state and
excited states.
Tensor interaction at high-q is important due to
the pion-exchange nature.
→ Higher orbits in the Shell-Model are involved.
→ The extent of the wave-function of the correlated
component (high-q) is spatially smaller than the
description of the Shell-Model.
Many fragmented strengths may be created by
coupling to this configuration. Due to the
complex configuration, decay width may become
smaller comparing with usual S.M. prediction.
Illustrative concept of the
pionic correlation in nuclei
H. Toki et al.
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We focus on the A=4 system (4He) because
• 4He is the lightest LS-closed shell nucleus.
GT strength is not expected in a naive shell model structure.
• Theoretical calculation is relatively easier than for heavier nuclei.
Precise calculation with modern NN interaction is possible.
• No 1+;T=1 state is found in 4He.
- Found in 16O and 40Ca.
- A 1+;T=0 state is known in 4He.
• No narrow (~100 keV) excited state is found in 4He.
→ Experimental search for narrow GT states in the A=4 system.
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Simulation of the Type II supernova and GT in 4He
Supernova do not successfully explode in simulations up to now.
More energy deposit of neutrinos in the star, called neutrino heating,
is required.
In the present scenario, n+N
C.E. reactions is the dominant
process of the neutrino heating.
4He
T. Kajino, INPC2007
4He(n ,
t
nt’)4He*(GT)
nt: nm and vt
GT strength is NOT
included in the simulations.
If it exists with sufficient
strength, B(GT)~0.1, the
neutrino inelastic scattering on
4He becomes the dominant
process.
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Existing (p,n) Data
4He(p,n)4Li
at 200 MeV
Palarczyk et al., PRC58, 645 (1998)
A GT strength of B(GT)~0.1 corresponds to an area of the hatched region in
the 4He(p,n) spectrum.
The main component is identified as a superposition of GDR and SDR (L=1).
Up to now, no GT strength nor a narrow peak has been observed.
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Schematic energy diagram of the A=4 system
(n,n’)
high-resolution
This experiment is dedicated to finding a narrow GT strength.
Extraction of broad GT strength is to be considered.
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Experimental Method
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4He(3He,t)
Measurement at RCNP
Spectrometer
Grand Raiden
in overfocus mode
The beam was
stopped here.
ejectile
tritons
4He
target cell: 20mmt
4He at 3atm
at Liq.N2 temperature
Aramide foil: 6mm
Achromatic beam is used
→ Resolution ~ 100 keV
3He
beam
at 420 MeV
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Experimental Results
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12N(g.s.)
Obtained spectra
4He+Aramid
Aramid
4He
100 keV
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4He+Aramid
Aramid
4He
4He(3He,t)
No narrow peak is observed in the present analysis.
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(A.U.)
Comparison with the (p,n) data
(p,n)
(3He,t)
Amount of cross section which corresponds to
B (GT)~0.1 in the case of 1+;T=1 states.
Black: (p,n) at 200 MeV
Palarczyk et al., PRC58,
645 (1998)
Red: (3He,t) at 140 MeV/A,
0.0-0.5deg.
This experiment.
Normalized to the (p,n) data.
Ex is adjusted.
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1.5-2.0 deg
1.0-1.5 deg
0.5-1.0 deg
0.0-0.5 deg
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Angular distribution for each excitation energy bin
4
3
4
He( He,t) Li
0-2MeV
10.0
2-4MeV
4-6MeV
6-8MeV
8-10MeV
d2s/dWdE (mb/sr/MeV)
10-12MeV
12-13MeV
1.0
0.1
0.0
0.2
0.4
0.6
0.8
q (fm-1)
1.0
1.2
1.4
Illustration of
the angular
distribution
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GT (1+;T=1) strength in 4He (prediction)
1+; T=1
Predicted strength is much
smaller than B(GT)=0.1.
Calc. by W. Horiuchi
4-body calc. with corr. Gaussian basis
NN-Int: G3RS
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Summary
• The GT strengths in the A=4 system, possibly having
narrow a narrow width, were searched for by the
4He(3He,t) reaction.
• Possible existence of the GT strengths is interesting in
nuclear physics, and may affect the present scenario of the
supernova explosion.
• In the present analysis, no narrow peak or structure has
been well observed.
• Extraction of broad GT strength is to be tried.
Reaction calculations and additional data are required.
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狭いピークは存在するか？
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狭いピークは存在するか？
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Comparison with the (p,n) data
Black: (p,n) at 200 MeV
Palarczyk et al., PRC58,
645 (1998)
Red: (3He,t) at 140 MeV/A,
0.0-0.5deg.
This experiment.
Normalized to the (p,n) data.
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Angular Distribution
R = 1.67 fm
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Estimation of the Single Particle Decay Width
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Experimental Data
•
•
•
•
•
•
•
4He(3He,t)
... no data
4He(p, n)
... poor resolution (600 keV)
4He(7Li, 7Be g)
... good sensitivity to DL=0, DT=1, and decomposition of DS
poor resolution (500 keV)
poor statistics for the DS=1 data
relatively favors DS=1 (factor of 5 comparing with (3He,t) at 140 MeV/U)
4He(p, p’)
... relatively good resolution (140 keV), finite scattering angle (favors DL=1),
dominant contribution of GDR (incl. Coulomb excitation)
4He(e, e’)
... little data, poor statistics
p+3He resonant scattering
... good resolution (~25 keV), limited Ex range, favors DL=1
4He(g,n), 4He(g, p)
... several experiments, but poor statistics, favors E1
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Neutrino Heating
爆発に必要な量の10-100分の１
shock-wave の外側には4Heがあるが、
主な寄与は、
4He+n
4
*
m/t → He +nm/t
と考えられており、その寄与は上の反
応の10分の1以下と見積もられている。
Bruenn and Haxton, Astro. J. 376, 678 (1991)
種々のL>=1の励起状態を入れても、
4Heによる寄与は10-30%増加するのみ。
Gazit and Barnea, PRC70,048801(2004)
S.W. Bruenn and W.C. Haxton,
Astro. J. 376,678(1991)
しかし、GTの寄与は計算に入っていな
い
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GT Strengths in 4He and Delayed-Explosion of Supernovae
Critical energy transfer rate for the delayed
explosion:
duc/dt = 2000 MeV/s/nucleon
In the present simulation
ne+N: 10-100 MeV/s/nucleon
nt+4He: 1-3 MeV/s/nucleon
nt = nm and nt
If B(GT)=0.01 is located at Ex=30 MeV
nt+4He → 100 MeV/s/nucleon
Thus nt+4He contribution is enhanced by an
order of ~2 and becomes the dominant one.
The possible B(GT) strength dramatically
changes the present supernovae scenario.
S.W. Bruenn and W.C. Haxton,
Astro. J. 376,678(1991)
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Delayed Explosion
Rn: neutrino sphere radius
Rg: gain surface
Rs: shock radius
Kotake 2006, pp. 987.
ニュートリノによるエネルギー放出
(~1053erg)の1%を星内物質に落とすことが
できれば超新星は爆発する
Rgより外側の物質がコ
アから放出される
ニュートリノによって加
熱され(neutrinoheating)、shock wave
の拡大を支える。
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4He
density distribution, form factor,
Y. Ogawa et al.
Y. Ogawa et al.
Charge and parity projected RMF model with pion
Successful description of the 4He g.s.
T. Myo et al.
Incorporation of tensor correlation in S.M.
4He+n phase shift
4He+n
phase shift, T. Myo et al.
E. Hiyama et al.
Gaussian Expansion Method (GEM)
Four nucleon system
Realistic NN interaction
Precise calculations of the 4He g.s. and exited states
4He
0+2 inelastic
form-factor,
E. Hiyama et al.
at Bonn, August 31,
Possible contribution from GTFB19
excitation
of2009
4He
4He(p,n)4Li
at 200 MeV
Data from Palarczyk et al., PRC58, 645 (1998)
B(GT)=0.1があればおよそこの面
積程度に対応
B(GT)~0.1程度あれば、4He(n,n’) がニュートリノヒーティ
ングの主役に躍り出る
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Energy Levels of 4He
D.R. Tilley, NPA541,1(1992)
Isospin of the GT states in
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58Cu
H. Fujita et al., PRC75,034310(2007).
Isospin decomposition by comparison between
58Ni(3He,t) and 58Ni(p,p’) strengths
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28Si
GDR
The same GDR fine structure is observed in different experiments.
gamma absorption data: H. Harada et al., J. Nucl. Sci. Tech38_465(2001).
(p,p’) data: from E249 at RCNP, H. Matsubara et al.
28Si: Sp=11.6 MeV, Sn=17.2 MeV
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Collaborators
Experiment Group:
T. Adachi
RCNP, Osaka University
K. Fujtia
RCNP, Osaka University
K. Hatanaka
RCNP, Osaka University
M. Kato
RCNP, Osaka University
T. Kawabata
CNS, Univ. of Tokyo
H. Matsubara
RCNP, Osaka University
H. Okamura
RCNP, Osaka University
H. Sakaguchi
Dep. of Applied Physics, Miayazaki University
Y. Shimbara
Dep. of Physics, Niigata University
K. Suda
RCNP, Osaka University
Y. Tameshige
RCNP, Osaka University
M. Yosoi
RCNP, Osaka University
Theory Group
H. Toki
E. Hiyama
T. Myo
Y. Ogawa
RCNP, Osaka University
Dep. of Physics, Nara Women’s University
RCNP, Osaka University
RCNP, Osaka University
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Fine-structure of the Gomow-Teller GR
58Ni(p, n)58Cu
•狭い幅(~100 keV)
Ep = 160 MeV
Counts
•非常に多くの状態へのフラグメント
GT(1+;1)=p(0-;1)＋(L=1)
J. Rapaport et al.
NPA (‘83)
58Ni(3He,
t)58Cu
E = 140 MeV/u
Y. Fujita et al.,
EPJ A 13 (’02) 411.
H. Fujita et al.,
PRC 75 (’07) 034310
0
2
4
Sp
6
8
10
12
14
Excitation Energy (MeV)
Experiment
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Cooled gas-target system developed by H. Matsubara et al.
4He
target cell: 20mmt
4He at 3atm at Liq.N temperature
2
Aramide foil: 6mm
Beam on Ar-gas
Beam on 4He-gas
with another
target-cell
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4Heのg.s.はどの程度0s4か？
Pion Role in Nuclei
H. Toki et al.
Pion contribution to B.E.
70 ~ 80 %
4HeのGT励起
強度の存在?
GFMC calculation of light nuclei
C. Pieper and R. B. Wiringa, Annu. Rev. Nucl. Part. Sci.51(2001), nucl-th/0103005
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Dedicated experiment is necessary with careful exp. consideration for the search
of narrow GT strengths with small cross section
4He(3He,t)
at 0 deg. is the best probe to search narrow GT strengths
good energy resolution (50-100 keV)
selectively excites DT=1 states
favors DS=1 in the intermediate energy region
suppression of DL>=1 excitations at 0 deg.
4He(p,p’)
at 0 deg. helps the identification of states
good energy resolution (50-100 keV)
reaction mechanism is simpler than (3He,t)
favors DS=1 in the intermediate energy region
but large contribution of GDR is expected by Coulomb excitation
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概要
A=4系に(幅の狭い)GT励起状態はあるのか？
・E306(RCNP): Search for narrow Gamow-Teller states in the A=4 nuclei
A. Tamii, Y. Fujita, H. Toki et al.,
• 4He(３He,t)4Li, 4He(p,p’) 実験
• 4He からの狭いGT励起を観測する
→ 土岐氏からのstimulation
• πを陽に含んだ核のモデルの定性的研究の予想
(一般的な認識には反する予想)
• 存在すれば、原子核物理の研究として面白い
• Supernova 爆発のメカニズムに重大な影響を与える可能性がある。