Recent progress of hypernuclear physics

E. Hiyama (RIKEN)

Hypernuclear physics has recently become very exciting owing to new epoch-making experimental data.

Recent progress in hypernuclear physics from a theorist’s viewpoint. ( of hypernuclear structure.)

Nuclear chart with strangeness

Λ

Multi-strange system such as Neutron star Λ

The major goal of hypernuclear physics

Fundamental and important for the studyof nuclear physics

To understand the baryon-baryon interaction, two-body scattering experiment is most useful.

YN and YY potential models so far proposed (ex. Nijmegen, Julich, Kyoto-Niigata) have large ambiguity.

1) To understand baryon-baryon interactions

Total number of Nucleon (N) -Nucleon (N) data: 4, 000

・ NO YY scattering data

・ Total number of differential cross section Hyperon (Y) -Nucleon (N) data: 40

Therefore, as a substitute for the 2-body

limited YN and non-existent YY scattering data,

the systematic investigation of the

structure of light hypernuclei is essential.

Hypernuclear g-ray data since 1998 (figure by H.Tamura)

・ Millener (p-shell model), 　・ Hiyama (few-body)

In S= -1 sector, what are the open questions in 　 YN interaction?

(1) Charge symmetry breaking

(2) ΛN － ΣN coupling

・ E13 “γ-ray spectroscopy of light hypernuclei”

by Tamura and his collaborators 11B 4HeΛ Λ

・ E10 “Study on Λ-hypernuclei with the doubleCharge-Exchange reaction”

by Sakaguchi , Fukuda and his collaboratiors

9HeΛ6HΛ

J-PARC : Day-1 experiment JLAB

Non-strangeness nucleiN Δ

N N

N

Δ

300MeV

80MeVΛ

Σ

On the other hand, the mass differencebetween Λ and Σ is much smaller, thenΛ 　 can be converted into Σ particle easily.

Nucleon can be converted into Δ.However, since mass difference betweennucleon and Δ is large, then probabilityof Δ in nucleus is not large.

ΛN

N Λ

Σ

Interesting Issues for the ΛN-ΣN particle conversionin hypernuclei

(1)How large is the mixing probability of the Σ particle in the hypernuclei?

(2) How important is the Λ Ｎー Σ Ｎ coupling in the binding energy of the Λ hypernuclei?

-BΛ-BΛ

0 MeV 0 MeV3He+Λ 3H+Λ

1+

0+

-2.39

-1.24

-2.040+

1+

-1.00

Exp. Exp.

4HeΛ

4HΛ

N

N

N

Λ

4HeΛ

4HΛ

n

　 Λ

3H (hyper-triton)Λ

p

n+p+Λ

d+Λ

0.13 MeVJ=1/2+

Exp.

These hypernuclei are suited forstudying ΛN-ΣN coupling.

n

　 Λ

n

nnΛ 　 breakup threshold

?They did not report thebinding energy.

Observation of nnΛ system (2013)This is also important to get information on ΛN-ΣN coupling.

scattering length:-2.68fm

nn unbound

　　　　　　　　　　　　　　

three-body calculation of 3nΛ

n

　 Λ

n E. Hiyama, S. Ohnishi,B.F. Gibson, and T. A. Rijken,PRC89, 061302(R) (2014).

What is interesting to study nnΛ system? n

　 Λ

n

S=0

The lightest nucleus to have a bound state is deuteron.

n p

n+p threshold

J=1+

-2.22 MeV

S=-1 (Λ 　 hypernucear sector)

n

　 Λ

3H (hyper-triton)

d

Λ

n+p+Λ

d+Λ

0.13 MeV J=1/2+

Exp.

Exp.

Lightest hypernucleus to have a bound statep

n

　 Λ

n

nnΛ 　 breakup threshold

?They did not report thebinding energy.

Observation of nnΛ system (2013)One of the lightest bound hypernuclei　

scattering length:-2.68fm

nn unbound

n

　 Λ

n

NN interaction : to reproduce the observed binding energies of 3H and 3He

NN: AV8 potentialWe do not include 3-body force for nuclear sector.

Theoretical important issue: Do we have bound state for nnΛ system? If we have a bound state for this system, how much is binding energy?

nnΛ 　 breakup threshold

?They did not report thebinding energy.

How about YN interaction?

n

　 Λ

n n n

　Σ+

YN interaction: Nijmegen soft core ‘97f potential (NSC97f) proposed by Nijmegen group reproduce the observed binding energies of 3H, 4H and 4He ΛΛΛ

To take into account of Λ 　 particle to be converted intoΣ particle, we should perform below calculation usingrealistic hyperon(Y)-nucleon(N) interaction.

n p

Λ

3HΛ

d+Λ

-0.13 ±0.05 MeV

1/2+

Exp.

1/2+

-0.19 MeV

Cal.

0 MeV

-BΛ

-BΛ -BΛ

0 MeV 0 MeV3He+Λ 3H+Λ

1+

0+

-2.39

-1.24

-2.04 0+

1+

-1.00

Exp.Exp.

4HeΛ 4H

Λ

-2.28

-0.54

-2.33

-0.57

0+

1+

0+

1+

Cal. Cal.

n

p

p

Λ

4HeΛ4H

Λ

Λ

What is binding energy of nnΛ?

n

p

n

Λ

nnΛ threshold 1/2+

We have no bound state in nnΛ system.This is inconsistent with the data.

Now, we have a question.

Do we have a possibility to have a bound state in nnΛ system tuningstrength of YN potential ?

0 MeVn

　 Λ

n

It should be noted to maintain consistency with the binding energiesof 3H and 4H and 4He.

ΛΛ Λ

-BΛ

VT ΛN-ΣN X1.1, 1.2

n

　 Λ

n

VT ΛN-ΣN VT ΛN-ΣNX1.1 X1.2

When we have a bound state in nnΛ system, what are binding energies of 3H and A=4 hypernuclei?

Λ

n

　 Λ

n

np

Λ

n

p

Λ

n

We have no possibilityto have a bound statein nnΛ system.

Question: If we tune 1S0 state of nn interaction,Do we have a possibility to have a bound state in nnΛ?In this case, the binding energies of 3H and 3He reproducethe observed data?

n

　 Λ

nT=1, 1S0 stateI multiply component of 1S0 state by 1.13 and 1.35. What is the binding energies of nnΛ ？

Some authors pointed out to have dineutron bound state innn system. Ex. H. Witala and W. Gloeckle, Phys. Rev. C85, 064003 (2012).

nnunbound

-0.066MeV

0 MeV

-1.269 MeV1S0X1.13

1S0X1.35

nnΛ

1/2+

unbound unbound

-1.272 MeV

n

　 Λ

n

N+N+N

1/2+

-13.93 (-13.23)MeV-8.48 (-7.72)

Exp.1/2+

3H (3He)

Cal.

-7.77(-7.12)-9.75 (-9.05)

We do not find any possibility to have a bound statein nnΛ.

Cal.Cal.

n n0 MeV

Summary of nnΛ 　 system:Motivated by the reported observation of data suggestinga bound state nnΛ, we have calculated the binding energy of this hyperucleus taking into account ΛN-ΣN explicitly.We did not find any possibility to have a bound state in thissystem. However, the experimentally they reportedevidence for a bound state. As long as we believe the data, we should consider additional missing elements in the present calculation. H. Garcilazo and A. Valcarce, PRC89, 057001(2014).A. Gal and H. Garcilazo, PLB736, 93 (2014).They concluded to have no bound state in nnΛ system.

It is planned to perform an improved experiment of nnΛ system at HypHI collaboration+Super FRS in 2018.

Furthermore, it should be noted that a direct measurement of nnΛ by the (e,e'K+) reaction can be possible at JLab. If we have a bound state for this system, it is important toget information on ΛN-ΣN coupling.

For this purpose, it is a quite important measurement theoretically as well as experimentally.

n n

Λ

n n

np3H 3nΛ

(e,e’K+)

S=-2 hypernuclei and

YY interaction

Λ+ ・・・・

It is conjectured that extreme limit, which includes many Λs in nuclear matter, is the core of a neutron star.

In this meaning, the sector of S=-2 nuclei , double Λ hypernuclei and Ξ hypernuclei is just the entrance to the multi-strangeness world.

　 However, we have hardly any knowledge of the YY interaction　 because there exist no YY scattering data.

Then, in order to understand the YY interaction, it is crucial to study the structure of double Λ hypernuclei and Ξ hypernuclei.

What is the structure when one or more Λs are added to a nucleus?

nucleus

ΛΛΛΛ

+ + +

So far, we have discussed about single Λ hypernuclei.

Before 2000

αΛΛ

8Be

ΛΛ

10BeΛΛ

11B

ΛΛ

13BΛΛ

Only three double Λ hypernuclei

There was NO observed double Λ hypernuclei without ambiguity.

Ambiguity for identifying these double Λ hypernuclei

Uniquely 　 identified 　 without 　 ambiguity for 　 the first time

α+Λ+Λ

0+

　　　 In 2001, the epoch-making data　　 has been reported by the 　　　 KEK-E373 experiment.

Observation of 　 6HeΛΛ

αΛΛ

６．９ 1±0.16 MeV

use Suggest reducing the strength of spin-independent force by half

compare between the theoretical resultand the experimental data of the biding energy of 6He

①

②

③

prediction of newdouble Λ hypernuclei

Strategy of how to determine YY interaction from the study of light hypernuclear structure

YY interaction Nijmegen model D　

Λ Λα

Accurate structure calculation

Spectroscopic experiments Emulsion experiment (KEK-E373) by Nakazawa and his collaborators

6HeΛΛ

④ ΛΛ

comparison

My theoretical contributionusing few-body calculation

・ E07 “Systematic Study of double strangness systems at J-PARC” by Nakazawa and his collaborators

Approved proposal at J-PARC

Emulsion experimentTheoretical calculation input: ΛΛ interaction to reproduce the observed binding energy of 　 6HeΛΛ

the identification of the state

It is difficult to determine (1) spin-parity

(2) whether the observed state is the ground state or an excited state

KEK-E373 experiment analysis is still in progress.

Successful example to determine spin-parity ofdouble Λ hypernucleus --- Demachi-Yanagi event for 10Be

Demachi-Yanagi event

8Be+Λ+Λ

ground state ?excited state ?

Observation of 　 10Be --- KEK-E373 experiment

ΛΛ

ΛΛ

ααΛ Λ

10BeΛΛ

10BeΛΛ

11.90±0.13 MeV

Successful interpretation of spin-parity of

E. Hiyama, M. Kamimura,T.Motoba, T. Yamada and Y. YamamotoPhys. Rev. 66 (2002) , 024007

Demachi-Yanagi event

ααΛ Λ

11.90

11.83

-14.70

α+Λ+Λ

6.91 ±0.16 MeV

αΛΛ

α x

Λ Λ x = n p d t 3He= = = = =

7He 7Li 8LiΛΛ ΛΛ ΛΛ8Li 9BeΛΛ ΛΛ

Hoping to observe new 　 double Λ hypernuclei in future experiments, I predicted level structures of these 　 double Λ hypernuclei within the framework of the α+x+Λ+Λ 4-body model.

E. Hiyama, M. Kamimura, T. Motoba, T.Yamada and Y. Yamamoto

Phys. Rev. C66, 024007 (2002)

Spectroscopy of ΛΛ-hypernuclei E. Hiyama, M. Kamimura,T.Motoba, T. Yamada and Y. YamamotoPhys. Rev. 66 (2002) , 024007

I have been looking forward to having new data in this mass-number region.

Future Subjects

In S=-2 sector, what subjects should be studied?

1)ΛΛ-ΞN coupling

One of the major goals in hypernuclear physics :To study the structure of multi-strangeness systems (extreme limit : neutron star)

NN

N N

Λ ΛΛΛΛ

N

NN

Multi-strangeness systems

25MeVΛΛΞN

threshold energy differenceis very small !

ΛΛ→ΞN particle conversion is is strong in multi-strangeness system. 　

300MeV

NN

ΔN

For the study of ΞN interaction, it is important to studythe structure of Ξ hypernuclei.

Ξ-

corenucleus

2) ΞN interaction

Recently, we observed bound Ξ hypernucleus, for the first timein the world. Next, it is important to predict theoretically what kinds of Ξ hypernuclei will exist as bound states.

Ξ-

14N

14N-Ξ-

-4.38 ± 0.25 MeV

0 MeV

For this purpose, recently, I studied these Ξ hypernuclei.

(d+Ξ-)

α

ΞN interaction to reproduce the experimental data of 12C(K-,K+) reaction　　・ T. Fukuda et al. Phys. Rev. C58, 1306, (1998);　　 ・ P.Khaustov et al. Phys. Rev. C61, 054603 (2000).

(ESC04)

Ξ-

Ξ- Ξ-n

Ξ- αpn np

(t +Ξ-)-(

p

n n

( ５ Li+Ξ-)

(6He+Ξ-)

Ξ-

α αΞ- tα α

n

(9Be+Ξ-) (11B+Ξ-)

-

Spectroscopy of Ξ hypernuclei at J-PARC

(pn +Ξ) (pnn+Ξ) -2 d+Ξ

t +Ξ

1/2 +

0+

1+

αn+Ξ

2-

1- (α+Ξ)+nn

1/2+(8Be+Ξ) +n

2-

11B+ Ξ

1-

1-

2-

(5He+Ξ) (6He+Ξ) ( ９ Be+Ξ) (11B+Ξ )

Ξ- tα α

Ξ- nα ααΞ-

n nnΞ-

αΞ-

n np

pΞ-

n

-5

0

-10

MeV

-20

Multi-strangeness systemsuch as Neutron star

Concluding remark

GSIJLabDAΦN EJ-PARC

J-PARC

In 2018, International Conference on hypernuclear physicswill be held in JLab.We expect to have many new data from JLab and J-PARC etc.New data will contribute to the development of hypernuclear physics.

Many new data were reported at this conference.

Thank you!

Neutron star

10kmMass ～ 1.5 ｘ solar mass

So far, it was considered that

Neutron star

neutron

proton

hyperon

Almost:neutrons

protons

hyperonselectrons

In hypernuclear physics, it is one of important subject to understand the mass of neutron star and structure of neutron star.

Nature 467 (2010) 1081 　 J1614-2230

　　 mass ＝ (1.97 ± 0.04)Msun

S1/2

P3/2

n n p p Λ Λ Ξ-

PauliForbidden

　・ 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).

p

6HeΛΛ

VΛΛ-ΞN

(3 protons in S1/2)

Effect of ΛΛ － ΞN coupling is small in 　 6He which was observed as NAGARA event.

ΛΛ

4H 5H ( 5He)ΛΛ

・ I.N. Filikhin and A. Gal, Phys. Rev. Lett. 89, 172502 　 (2002)

・ Khin Swe Myint, S. Shinmura and Y. Akaishi, Eur. Phys. J. 　 A16, 21 　(2003).

・ D. E. Lanscoy and Y. Yamamoto, Phys. Rev. C69, 014303 　 (2004).

・ H. Nemura, S. Shinmura, Y. Akaishi and Khin Swe Myint, 　 Phys. Rev. Lett. 94, 202502 (2005).

Λ Λn

nΛΛ

Λ Λ

pnΛΛ

For the study of ΛΛ － ΞN coupling interaction,

4H and 5H ( 5He) are very suitable.ΛΛ ΛΛ ΛΛ

p

S1/2

P3/2

5HΛΛ

n n p Λ Λ Ξ- p

5HΛΛ

V ΛΛ － ΞN

(2 protons in S1/2)

Due to NO Pauli plocking, the ΛΛ － ΞN coupling can be large in 5HΛΛ

B.F. Gibson, I.R. Afnan, J.A.Carlson and D.R.Lehman,Prog. Theor. Phys. Suppl. 117, 339 (1994).

Λ Λn

np

In this way, the study of structure of 　 4H, 5H and 5He

is important for the study of ΛΛ ー ΞN coupling.

・ E07 “Systematic Study of double strangness systems at J-PARC” by Nakazawa and his collaborators

Approved proposal at J-PARC

In this meaning, the experiment at J-PARC will be important.

We expect to have many double Λ hypernuclei in the future.

ΛΛ ΛΛ ΛΛ

neutron

proton

hyperon

For this study, we need

(1) Nucleon-Nucleon interaction

(2) Hyperon-Nucleon Hyperon-Hyperon interaction

To determine the interactions in unified way: one of the primary goals of the hypernuclear physics

n p n Λ Λ Λ n Ξ

pp In order to determine the interactions, two-body

Scattering experiment is most useful.

In fact, for this purpose, many nucleon-nucleon scattering experiments have been done so far.

N We have much knowledge.N

n Λ Λ Λ n Ξ

nΛ Λ Λ

However, due to the difficulty of performing two-body hyperon-nucleonand hyperon-hyperon scattering experiments, we have small number ofhyperon-nucleon scattering data and NO hyperon-hyperon data.

We have little knowledge about the interactions up to now.

Hyperon-nucleon and hyperon-hyperon potential models so far proposed. (ex. Nijmegen,Julich, Kyoto-Niigata)Large ambiguity.