Recent status in Hypernuclear Physics

E. Hiyama (Nara Women’s Univ.)

The discussion about the recent progress in thehypernuclear physics by introducing my studiesperformed so far.

My study

nucleus

Λ

nucleus

Λ Λ

Single Λ hypernucleus Double Λ hypernucleus

In 2008 (next year), the construction of J-PARC facilityis complete.And the experiment about hypernuclear physics will berun since 2008.

So, we expect to have a lot of data of hypernucleiin the future.

What are interesting and important to study Hypernuclear physics?

Before answering this question, firstly I intoruduce theobtained hypernuclear experimental data so far.

Before 1995

(1) hyperon(Y)-nucleon(N) and hyperon(Y)-hyperon(Y) scattering data

Hyperon-nucleon scattering experimental data obtained so far

Total number of data:40 NN:4,000

No YY scattering data (Due to the difficulty of the YN and YYscattering experiment)

(2) How many single Λ hypernuclei and doubleΛ hypernuclei were observed so far?

Nuclear chart ofa single Λ hypernuclei

About 30 events

Double Λ hypernuclei

6He , 　　　 10Be, 　 13BΛΛ ΛΛ ΛΛ

There are ambiguities in identifying thesedouble Λ hypernuclei.

(3) How many γ transitions were measured?

0+

1+5/2+

1/2+0+

2+

0+

1-

4HΛ7LiΛ 9BeΛ

13CΛ

γγ γ

γ Only excitation energies were measured.

B(E2) and B(M1) values NEVER havebeen observed.

Since 1995

We have been obtaining epoch-making experimental data continuously because of development of experimental method,especially, development of high resolution γ-ray spectroscopymethod with Ge detector.

Some of the recent epoch-making experimental data

(1)For the first time, the B(E2) value in 7Li was successfully observed by KEK-E419.

6Li

Λ

7LiΛ

As a consequence, we could extract the hypernuclear sizefor the first time.

Λ

(2) γ-ray spectroscopic experiments of 9Be and 13C were successfully performed at BNL-E929 and E930.

Λ Λ

8Be

Λ

12C

Λ

9Be 13CΛ Λ

As a result, we could determine the strength of ΛN spin-orbitforce.

(3) At KEK-E373 experiment, a double Λ hypernucleuswas observed and was identified uniquely 6He.ΛΛ

α

Λ Λ

6HeΛΛ

This is the first observation of doubleΛ hypernuclei with NO ambiguity.

Furthermore,At J-PARC, we are planning to have many single Λ hypernuclei and double Λ hypernuclei in the future.

Why is it important to produce many single Λ hypernuclei and double Λ hypernuclei?

Major goal of hypernuclear physics

(1)To understand the hyperon(Y)-nucleon(N) and hyperon(Y)-hyperon(Y) interaction

(2) To study new dynamics of many body systems consisting of nucleons and hyperons

The J-PARC facility is the key facility to provide the datanecessary to attain the goal of hypernuclear physics.

But since the scattering YN scattering data is limited,then it is necessary to obtain information on YN and YY interactionsfrom the hypernuclear structure study.

For this purpose, we need to have many hypernuclei and doubleΛ hypernuclei.

The J-PARC facility is the key facility to provide the datanecessary to attain the goal of hypernuclear physics.

My role To use high precision calculational method of few-bodysystems to carry out the goal (1) and (2).

Gaussian Expansion Method Developed by Kyushu Univ. group Kamimura(1) 3-cluster structure of light nuclei(2) Coulomb 3-body muonic molecular ions appearing in the muon-catalyzed fusion cycles (1987 ～ )(3) 3-nucleon bound states with realistic NN and 3N forc

es (1988)(4)Metastable antiprotonic helium atom (He++p+e)(1995 ～ )

E. Hiyama, M. Kamimura and Y. Kino,Prog. Part. Nucl. Phys. 51 (2003), 223.

Applied to

This method also successfully applied to four-bodyproblems.

The merit of this method:(1)To calculate the energy of bound state very accurately(2) To calculate the wavefunction very precisely

One example

Benchmark test of 4HePhys. Rev.C64, 044001(2001)

n n

p p

NN:AV8

4He

4 nucleon bound state

Good agreement among 7different methodIn the binding energy, r.m.s, and two-body correlation function

Our method → hypernuclear structure

Major goal of hypernuclear physics

(1)To understand the hyperon(Y)-nucleon(N) and hyperon(Y)-hyperon(Y) interaction

Since YN scattering experiment are difficult to perform,the existing data is very limited.

So far proposed YN interactions have a large degree of ambiguity.

Nijmegen model, Julich modelQuark model based potential

It is necessary to obtain useful information on YN and YYinteraction from hypernuclear structure study.

Our calculation of few-body systems play essential rolein this connection between the basic models and the experimental data.

This theoretical component is our calculational contribution from few-body systems.

Discussion on γ-ray spectroscopy experiment and theoreticalstructure calculations of 9Be and 13C related to the YN spin-orbit interaction

Λ Λ

8Be

Λ

12C

Λ

9Be 13CΛ Λ

Strong NN spin-orbit force which leads to magic number nuclei

How large is the YN spin-orbit force compared with the NN spin-orbit force?

Meson theoryNijmegen model

«

Constituent quark modelProposed by Fujiwara et al.

If we use these types of spin-orbit forces in hypernuclearstructure calculation, then how is the spin-orbit energy splitting?

Why is the spin-orbit force is small based on the constituent quark model ?The strength of Antisymmetric LS(ALS) is opposite sighwith the symmetric LS(SLS).And that of ALS is cancelled that of SLS.

ALS : 　　　 σ ー　 σΛ N

2VALS

SLS: VSLSσ ＋　 σΛ N

2

O.Morimatsu et al.Nucl. Phys. A420,573 (1984)

Thus, quark model leads to small spin-orbit splitting energy in hypernuclear structure,

xL

xL

0+

2+

8Be

Λ

1/2+

5/2+

3/2+

ΔELssplitting

γ

γ

9BeΛ

BNL-E930

12C 13CΛ

γγ

1/2+

3/2-

1/2-

ΔEΛ

0+

BNL-E929

E. Hiyama et al.Phys. Rev. Lett. 85, 270 (2000)

8Be = α α

12C = α

α α

9Be=Λ

13C=Λ

α α

Λ

α

α α

Λ

ΛN spin orbit force and 9Be and 13CΛ Λ

5/2+

3/2+ 80

200keV

～5/2+

3/2+35

40keV

MesonQuark

9BeΛ

～

3/2-

1/2- 360

960keV

～

150

200keV

MesonQuark

13CΛ

～1/2-

3/2-

Exp.

5/2+

3/2+

31.4Exp.+2.5-3.6 keV

BNL-E930

H. Akikawa et al.Phys. Rev. Lett. 88,(2002)82501.

152

1/2-

3/2-

BNL-E929

± 54 ± 36 keVS.Ajimura et al.Phys. Rev. Lett. 86,(2001) 4255

When any new types of YN interaction are proposed in the future, it is desirable to pay attention to havinga reasonable strength of YN spin-orbit force by testing it in the structure calculation of 9Be and 13C.

Λ Λ

Where do we go from here?

How large are the ΣN and ΛΛ spin-orbit forces?

・ ΣN scattering experiments at J-PARC facility・ γ-ray spectroscopy experiments of double Λ hypernuclei

nucleus

Λ Λ

We are extracting novel information about YN interactionbecause of the cooperation analysis involving theγ-ray spectroscopy experiment and highly accurate calculations.

Once the Hamiltonian is determined, we can calculated precisely the structure of many-body systems consistingof neutron, proton and hyperon.

Furthermore, we can predict with understanding newphenomena such as we have never imagined before.

Major goal of hypernuclear physics

(1)To understand the hyperon(Y)-nucleon(N) and hyperon(Y)-hyperon(Y) interaction

(2) To study new dynamics of many body systems consisting of nucleons and hyperons

The J-PARC facility is the key facility to provide the datanecessary to attain the goal of hypernuclear physics.

(2) To study new dynamics of many body systems consisting of only nucleons

One of the major goal in neutron rich nuclear physics(to my knowledge)

In unstable nuclear physics

stable nucleus

n

n

When many nucleons are added tothe stable nucleus, how is structure?

nucleusHyperon(Λ 、 Ξ ・・ )

In hypernuclear physics

How is structure, when hyperons are added to the nucleus?

In this view point, we have the same interest both in studyingunstable nuclear physics and hypernuclear physics.

What is interesting in unstable nuclear physics?

cluster

N

cluster

Nucleus consisting of 2 clusters

one nucleon is added tothe nucleus

Pauli principle

The valence nucleon is locatedoutside the nucleus.

What is interesting in unstable nuclear physics?

cluster

N

cluster

Nucleus consisting of 2 clusters

N

N

More nucleons areadded to the nucleus ・・・

・ where are additional nucleons are located in the nucleus?

・ Do additional nucleonscontribute to the dynamicalchange of structure of 2 clusters?

・ Do additional nucleons affect to the critical stabilityof the nucleus?

Hypernuclear physics

Λ

Λ

Nucleus Hypernucleus

There is no Pauli Pricliple betweenN and Λ.

Λ particle can reachdeep inside, and attract the surrounding nucleonstowards the interiorof the nucleus.

Λ

γnucleus

hypernucleus As a results, if a Λ particle is added to the nucleus, theresultant hypernucleus willbecome more stable against the neutron decay.

Glue-like role of Λ particle

Glue-like role of Λ particle play a crucial role in binding energy mechanism, critical stability.

From the view point of the ‘critical stability’,

α

Λ

nn

N

N N

Λ Λ

N N

Λ

7HeΛ

4HΛ

4HΛΛ

αΛ

n

6HeΛ

Hypernuclear physics

Λ

Λ

Nucleus Hypernucleus

There is no Pauli Pricliple betweenN and Λ.

Λ particle can reachdeep inside, and attract the surrounding nucleonstowards the interiorof the nucleus.

Λ

γnucleus

hypernucleus As a results, if a Λ particle is added to the nucleus, theresultant hypernucleus willbecome more stable against the neutron decay.

Glue-like role of Λ particle

Example

α

n

+ Λ

5He:ground state isunbound

αΛ

n

6HeΛ

ground state is bound.

α

n n

6He:famous halo nucleus

+ Λα

Λ

nn

7HeΛ

α +n

0.89 MeV P3/2

Λ

5He+nΛ -3.12 MeV1-

α +n+Λ0 MeV

5He

6HeΛ α Λ

L=05HeΛ

0.17 MeV

α

Λn

6HeΛ

How do the 3 particle locate to each other ?Is there neutron halo in 6He hypernucleus?Λ

n halo ?

密度　　 ρn(r) = ∫|Ψ(6He)|2dRdr^

r

Λ

α

Λ

n

r.m.s α-Λ 2.8 fm α-n 5.0 fm

Halo nucleus 6Heα-n 4.5 fm

Larger than 6He

Example: 7He

α

N N 6He : One of the lightest n-rich nuclei

α

N NΛ 7He: One of the lightest

n-rich hypernuclei

Λ

Λ

No data

Phys. Rev. C53, 2075 (1996)

0+

2+

γ

α+n+n

-0.69

0 MeV

BΛ =5.44 MeV

(cal.)γ

1/2+

5/2+

7/2+

5He+n+nΛ

α+Λ+n+n0 MeV

-6.12

-4.43

Halo state

No data

6He 7HeΛ

E. Hiyama et al.

Prompt particle decay

0+

2+

γ

α+n+n

-0.69

0 MeV

BΛ =5.44 MeV

(cal.)γ

1/2+

5/2+

7/2+

5He+n+nΛ

α+Λ+n+n0 MeV

-6.12

-4.43

Halo state

No data

6He 7HeΛPrompt particle decay

5/2+ →1/2+

3/2+ →1/2+・ Useful for the study of the excitation mechanism in n-rich hypernuclei・ Helpful to the study of the excitation mechanism of the halo nucleusIn n-rich nuclei and n-rich hypernuclei, there will be many examples such as

Combination of 6He and 7He. I hope that γ-ray spectroscopy of n-rich hypernuclei will be performed at J-PARC.

Λ

S=0 N

NS=-1

Schematic illustration of the nuclear chart

S=0Most of the n-rich or p-rich nuclei near the drip line have halo- orskin-structure. Outside the drip line, there must be many nucleon-unbound states. What will happen, if we inject a Λ hyperon to those nuclei nearthe drip line?

S=-1

We can expect that the glue-like role of Λ extends the nucleon drip line to more outside.

N

N N

Λ Λ

N N

Λ

4HeΛ

4HΛΛ

Particle-conversion such as ΛN → ΣN is very important in critical stability of few-body hypernuclearsystems.

In non-strangeness nuclei

NN

N⊿

250 MeV

N

NN NN

⊿+

3H,3HeIt is well known that the ground state of 3H and 3He are deeplyBound without contribution.⊿

Single Λ hypernuclei

NN

N⊿

250 MeV

80 MeV

Λ

Σ

N

N N

Λ4He

Λ

N

N N

Σ

+

If NNNΣ channel is neglected, then the ground state of 4He isbound or unbound?

Λ

From view point of “critical stability”, theparticle-conversion such as ΛN→ΣN isvery important in the binding mechanism of few-body hypernuclear systems.

N

N N

Λ4He

N

N N

Σ

+

80 MeV

Λ

Σ

N

N N

Λ4He

Λ

N

N N

Σ

+

・ Y.Akaishi et al., Phys. Rev. Lett. 84, 3539(2000).

・ E. Hiyama et al., Phys. Rev. C65, 011301 (R) (2001).

・ H. Nemura et al., Phys. Rev. Lett. 89, 142504(2002).

・ A. Nogga et al., Phys. Rev. Lett. 88, 172501(2002).

ΨJM(A=4)=ΣΦc(rc,Rc,ρc)N=1

8

4He, 4HΛ Λ

VNN : AV8 potential

VYN : Nijmegen soft-core ’97f potential

PΣ=2.21%

PΣ=1.12 %

N

N N

Λ4He

Λ

N

N N

Σ

+

N

N N

Λ4He

Λ

N

N N

Σ

+

Therefore, by solving the coupled 4-body problem ofA=4 hypernuclei, we found that the Σ-channel components play an essential role in the bindingmechanism of the A=4 hypernuclei.

NN

N⊿

250 MeV

80 MeV

Λ

Σ

ΞN

ΛΛ28 MeV

S=-2 nuclei

ΛΛ-ΞN particle conversion must be more important.

(1) Observation of 　 6He

Uniquely identified without ambiguity forthe first time

ΛΛ

α+Λ+Λ

7.25 ±0.1 MeV

0+

α

Λ Λ

NAGARA Event

2 epoch-making experimental data on double Λ hypernucleiAt KEK-E373 and BNL-E906.

KEK-E373

[2] Observation of 　 4HΛΛ

n p

Λ Λ

4HΛΛ

They observed the sequential weak decay from 4H.However, they could not determine the binding energy of 　 4H.

BNL-E906

ΛΛ

ΛΛ

n p

Λ Λ

4HΛΛ

The important issue: Does the YY interaction which designed to reproduce the binding energy of 6He make 4H bound?And how does the effect of ΛΛ ー ΞN coupling play important role in the binding energy of 6He and 4H?

ΛΛ ΛΛ

ΛΛ ΛΛ

1)I.N. Filikhin and A. Gal, Phys. Rev. Lett. 89, 172502(2002)2)H. Nemura, Y. Akaishi et al., Phys. Rev. C67, 051001(2002)

n

p

Λ

Λ

VΛΛ

α

Λ Λ

NOT BOUND !

4HΛΛ

6HeΛΛ

NAGARA event

α+Λ+Λ

7.25±0.1 MeV

0+

Did not include ΛΛ-ΞN coupling

ΛΛ-ΞN 　 coupling => ・ significant in 4HΛΛ

n p

Λ Λ

4HΛΛ

・ Not so important in 　 6HeΛΛ

α

Λ Λ 6HeΛΛ

S1/2

P3/2

6HeΛΛ

n n p p Λ Λ Ξ ０n

Forbidden

The effect of ΛΛ-ΞN coupling is small in 　 6He and thep-shell double Λ 　 hypernuclei 　・ I.R. Afnan and B.F. Gibson, Phys. Rev. C67, 017001 (2003). ・ Khin Swe Myint, S. Shinmura and Y. Akaishi, nucl-th/029090. ・ T. Yamada and C. Nakamoto, Phys. Rev.C62, 034319 (2000).

ΛΛ

V ΛΛ ー ΞN

S1/2 n p Λ Λ Ξ ０n

4HΛΛ

P3/2

allowed

(Ξ- p)

There is NO Pauli blocking and the ΛΛ ー ΞN effectcan be large.

n p

Λ Λ

N

N

N

Ξ

+

4HΛΛ

One of the most numerically difficult 4-body problem

E. HiyamaDr. Nemuran n

Λ Σ

n n

Σ Σ

E(MeV)

0

-3.12

-7.25 0+

Exp.(KEK-E373)

CAL.

5He+ΛΛ

α+Λ+Λ6He

ΛΛwith Pauli blocking

E(MeV)

n+p+Λ+Λ

3H+ΛΛ

NoExp.

unbound

NNΛΛchannel only NNΛΛ

+ 　 NNNΞ

PΞ=1.6%

0.1MeV

PΞ=3.2%

4H with no Pauli blockingΛΛ

α

0MeV

n p

Λ Λ

N

N

N

Ξ

+

4HΛΛ

From this fact, we found that ΛΛ-ΞN coupling is very important in “critical stability” of this 4-body system.I hope that search-experiment of this system will bedone at J-PARC in the future.

Conclusion

In the terms of my single Λ 　 and double Λ hypernuclear studies,I shall discuss the status of the recent progress in hypernuclear physics.

I hope that the hypernuclear experiment at J-PARC will be performed. J-PARC facility is the key facility to developthe hypernuclar physics.

At the end of next year (2008), first beam at J-PARCwill be run.And they are planning to perform the experiment abouthypernuclei in 2009.

So, it is expected that all experimentalists might beso busy.

If man-power of such experiments is not enough,I am ready for joining those experiments.

In 2002, KEK-E509I had 7 shifts for this experiments.

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12 / 2008

I shall be happy if I could join the future experiments at the J-PARC facility with this new film badge.

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Thank you!