fb19 at bonn, august 31, 2009 gamow-teller strength in the a=4 system a. tamii research center for...

FB19 at Bonn, August 31, 2009

Gamow-Teller Strength in the A=4 System

A. Tamii

Research Center for Nuclear Physics, Osaka University

1

-- Experimental search of GT states excited from the 4He nucleus, possibly having a narrow width --


CollaboratorsExperiment:

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


Contents• Motivation

– Narrow GT states and pionic correlation( ~ 100 keV)

– GT strength in 4He and delayed supernova explosion

• Experiment: 4He(3He,t)

• Preliminary Results

• Summary


Motivation


Fine Structure of the Gamow-Teller Resonance

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.

How these• large fragmentation• narrow widthscan be explained be theory?

↑

Sp

Y. Fujita et al., EPJ A 13, 411 (2002)GT: L=0, S=1, T=1transition: 0+ → 1+


Pionic Correlation in Nuclei

Illustrative concept of the 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.

H. Toki et al.


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.


Simulation of the Type II supernova and GT in 4He

4He(t,t’)4He*(GT)

T. Kajino, INPC2007

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 C.E. reactions is the dominant process of the neutrino heating.

4He 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.t: and v


Existing (p,n) Data4He(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.


Schematic energy diagram of the A=4 system

(,’)

This experiment is dedicated to finding a narrow GT strength.Extraction of broad GT strength is to be considered.

high-resolution


Experimental Method

FB19 at Bonn, August 31, 20094He(3He,t) Measurement at RCNP

The beam was stopped here.

Achromatic beam is used

→ Resolution ~ 100 keV

Spectrometer

Grand Raidenin overfocus mode

4He target cell: 20mmt

4He at 3atm at Liq.N2 temperatureAramide foil: 6m

3He beam at 420 MeV

ejectiletritons


Experimental Results


Obtained spectra

4He+Aramid

Aramid

4He

100 keV

12N

(g.s

.)


4He+Aramid

Aramid

4He

4He(3He,t)

No narrow peak is observed in the present analysis.


Comparison with the (p,n) data

Black: (p,n) at 200 MeVPalarczyk 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.

(p,n)(3He,t)

(A.U

.)

Amount of cross section which corresponds to B (GT)~0.1 in the case of 1+;T=1 states.


1.5-2.0 deg1.0-1.5 deg0.5-1.0 deg0.0-0.5 deg


Angular distribution for each excitation energy bin4He(3He,t)4Li

0.1

1.0

10.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

q (fm-1)

d2 s/d

WdE

(mb/

sr/M

eV)

0-2MeV

2-4MeV

4-6MeV

6-8MeV

8-10MeV

10-12MeV

12-13MeV

Illustration of the angular distribution


Calc. by W. Horiuchi4-body calc. with corr. Gaussian basisNN-Int: G3RS

Predicted strength is much smaller than B(GT)=0.1.

GT (1+;T=1) strength in 4He (prediction)

1+; T=1


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.

20


狭いピークは存在するか？


Comparison with the (p,n) data

Black: (p,n) at 200 MeVPalarczyk et al., PRC58, 645 (1998)

Red: (3He,t) at 140 MeV/A,0.0-0.5deg.This experiment.Normalized to the (p,n) data.


Angular Distribution

R = 1.67 fm


Estimation of the Single Particle Decay Width


Experimental Data

• 4He(3He,t)... no data

• 4He(p, n)... poor resolution (600 keV)

• 4He(7Li, 7Be )... good sensitivity to L=0, T=1, and decomposition of S poor resolution (500 keV) poor statistics for the S=1 data relatively favors S=1 (factor of 5 comparing with (3He,t) at 140 MeV/U)

• 4He(p, p’)... relatively good resolution (140 keV), finite scattering angle (favors L=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 L=1

• 4He(,n), 4He(, p)

... several experiments, but poor statistics, favors E1


Neutrino Heating

shock-wave　の外側には 4Heがあるが、主な寄与は、　　　　　4He+/ → 4He*+/

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。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。

Bruenn and Haxton, Astro. J. 376, 678 (1991)

Gazit and Barnea, PRC70,048801(2004)

しかし、 GTの寄与は計算に入っていない

爆発に必要な量の 10-100分の１

S.W. Bruenn and W.C. Haxton, Astro. J. 376,678(1991)


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

e+N: 10-100 MeV/s/nucleon t+4He: 1-3 MeV/s/nucleon

t = and

If B(GT)=0.01 is located at Ex=30 MeV t+4He → 100 MeV/s/nucleon

Thus t+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)


Delayed Explosion

R: neutrino sphere radiusRg: gain surfaceRs: shock radius

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(neutrino-heating) 、shock　wave　の拡大を支える。

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


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

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 density distribution, form factor, Y. Ogawa et al.

4He+n phase shift, T. Myo et al.

4He 0+2 inelastic

form-factor,E. Hiyama et al.

FB19 at Bonn, August 31, 2009Possible contribution from GT excitation of 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(,’) がニュートリノヒーティングの主役に躍り出る


Energy Levels of 4He

D.R. Tilley, NPA541,1(1992)


Isospin of the GT states in 58Cu

Isospin decomposition by comparison between58Ni(3He,t) and 58Ni(p,p’) strengths

H. Fujita et al., PRC75,034310(2007).

FB19 at Bonn, August 31, 200928Si GDR

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

The same GDR fine structure is observed in different experiments.


CollaboratorsExperiment 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. OkamuraRCNP, 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 RCNP, Osaka University E. Hiyama Dep. of Physics, Nara Women’s University T. Myo RCNP, Osaka University Y. Ogawa RCNP, Osaka University

36


58Ni(p, n)58Cu Ep = 160 MeV

58Ni(3He, t)58Cu E = 140 MeV/u

Cou

nts

Excitation Energy (MeV)0 2 4 6 8 10 12 14

Fine-structure　of　the　Gomow-Teller　GR

Y. Fujita et al.,EPJ A 13 (’02) 411.

H. Fujita et al.,PRC 75 (’07) 034310

Sp

J. Rapaport et al.NPA (‘83)

•狭い幅 (~100 keV)

•非常に多くの状態へのフラグメント

GT(1+;1)=(0-;1) ＋(L=1)

FB19 at Bonn, August 31, 2009ExperimentCooled gas-target system developed by H. Matsubara et al.

4He target cell: 20mmt

4He at 3atm at Liq.N2 temperatureAramide foil: 6m

Beam on Ar-gas Beam on 4He-gaswith another target-cell

FB19 at Bonn, August 31, 20094He の g.s. はどの程度 0s4 か？

Pion contribution to B.E.70 ~ 80 %

C. Pieper and R. B. Wiringa, Annu. Rev. Nucl. Part. Sci.51(2001), nucl-th/0103005

Pion Role in Nuclei

H. Toki et al.

4Heの GT励起強度の存在 ?

GFMC calculation of light nuclei


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 T=1 states

favors S=1 in the intermediate energy region

suppression of L>=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 S=1 in the intermediate energy region

but large contribution of GDR is expected by Coulomb excitation


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 nucleiA. Tamii, Y. Fujita, H. Toki et al.,

• 4He( ３ He,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。

fb19 at bonn, august 31, 2009 gamow-teller strength in the a=4 system a. tamii research center for...

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