-ray spectroscopy of the -ray spectroscopy of the sdsd-shell hypernuclei-shell hypernuclei

Graduate school of Science, Tohoku University

T. Koike

Hyperball-J collaboration

• Survey of sd-shell hypernuclear cores• -ray spectroscopy of well deformed hypernuclei

• 25Mg • Summary

1919FF

2020NeNe

2323NaNa

2424MgMg

2727AlAl

2828SiSi

3131PP

3232SS

3535ClCl

4040ArAr

3939KK

4040CaCa

3737ClCl

2626MgMg2525MgMg

2222NeNe

3030SiSi

3434SS

3939ClCl

3838ArAr

2323MgMg

2222NaNa

2727SiSi

2626AlAl

3030PP

3131SS

3434ClCl

3838KK

3939CaCaPossible sd-shell hypernuclei via -ray spectroscopy with

(K-,-) & (+,K+) reactions

Z

Z=20

Z=9

Most abundant isotopes (target)

abundance

proton decay

neutron decay

N

1919NeNe

1818FF

3939ArAr

3636ClCl

3636SS

2525NaNa2424NaNa

2121FF

2121NeNe

E13

Bound states of Bound states of sdsd-shell nuclei and hypernuclei-shell nuclei and hypernuclei

D. J. Millener et al., Phys. Rev. C, 38 2700 (1988)

• Co-existence of shell (mean field) and cluster-like structures • More valence nucleons

•higher level densities (especially odd-odd)

• Collective (rotational) excitation spectrum → low-lying energy •pstates also bound

• Shell model • Cluster model • Self-consistent calculations (12/4 Hagino)(12/4 Hagino)

•RMF•Hatree-Fcok+BCS

•AMD (12/4 Kimura)(12/4 Kimura)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

18F

19Ne

22Na

23M

g

24M

g

25M

g

26Al

27Si

30P

32S

34C

l

39Ar

38K

39C

a

(keV

)SnSpEx(plambda)

BnBnBpBpEx(pEx(p

Target A -1ZXn-1

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

18F

19Ne

23M

g

24M

g

25M

g

26Al

27Si

30P

32S

34C

l

39Ar

38K

39C

a

(keV

)

28Si

s

pd

(+,K+) T.Hasegawa et al., Phys. Rev. C 53, 1210 (1996)

AZA-1

Z-1 A-1Z

Weak decay

(mostly via non-mesonic in the sd-shell hypernuclei)

- coincidence with Hyperball-J

SKSMinus?

1919FF

2020NeNe

2323NaNa

2424MgMg

2727AlAl

2828SiSi

3131PP

3232SS

3535ClCl

4040ArAr

3939KK

4040CaCa

3737ClCl

2626MgMg2525MgMg

2222NeNe

3030SiSi

3434SS

3939ClCl

3838ArAr

2323MgMg

2222NaNa

2727SiSi

2626AlAl

3030PP

3131SS

3434ClCl

3838KK

3939CaCaPossible sd-shell hypernuclei via -ray spectroscopy with

(K-,-) & (+,K+) reactions

Z

Z=20

Z=9

Most abundant isotopes (target)

abundance

proton decay

neutron decay

N

1919NeNe

1818FF

3939ArAr

3636ClCl

3636SS

2525NaNa2424NaNa

2121FF

2121NeNe

even-even

mirror

E13

)2cossinsin3)1cos3((cos

16

51),( 22

0

RR

CollectiveCollectiveprolateprolate

(, =0°)

(0,0)

sphericalspherical

triaxialtriaxial

Non collective Non collective oblateoblate

(, =60°)

Skyrme Hartree-Fock +BCSSkyrme Hartree-Fock +BCS

• self-consistent mean field• Skyrme-type N interaction• PES of hypernuclei with triaxial deformation: E(E(,,)) • Angular momentum not good quantum number

Myaing Thi Win et al., submitted to PRC

24Mg, 24Mg+

0+

21+

41+

Spectra of a deformed Spectra of a deformed even-eveneven-even nucleus nucleus (collective excitation mode) (collective excitation mode)

E(41+)/E(21

+)

-band

02+

23+

43+

2, J

band

22+

31+

42+

vibrational

v.s.rotational

K=0, n=1, n=0

K=2, n=0, n=1

K=0, n=0, n=0

0

2

4

6

8

8 10 12 14 16 18 20Z

Exci

tatio

n en

rgy

(MeV

)

1st 2+2nd 2+2nd 0+

2211++, 2, 222

++, and 0, and 022++

26Si38Ar 38Ca

18(▲) ,20Ne 22(▲) ,24Mg

30S

Rotational v.s. VibrationalRotational v.s. Vibrational

E(4)/ E(2)

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

8 10 12 14 16 18 20 22Z

E(4)

/E(2

)

22Mg

24Mg

26Si 38Ar

18Ne

Rotational

Vibrational

38Ca20Ne

-ray spectroscopy of -ray spectroscopy of 2525MgMg

• Well deformed & even-even core hypernuclei– low and simple (regular) energy level– direct observation of core polarization effect of

• Nuclear density saturation at the g.s. with little change in size, but a shape can change in (,) plane

• A few 100 keV change• Observation of spin averaged 21

+, 22+, 02

+→ （ , ）• Observation of 41

+

• p -bound-states particle stable (Bp=11693keV Bn=16532 keV)

– Observation of p splitting in the sd-shell• Hyperball-J with LaBr, CsI detectors (?)

• Use of a natural target– possibility of increasing the number of accessible hypernuclei– a test case for heavier hypernucley beyond sd-shell

2424Mg level schemeMg level scheme

12C 13C 24Mg 25

Mg

pp

p

T=0 T=0

s p d

24Mg

(0+)

0.790.79 24Mg 23

Na 23Mg

core 23Mg 22Na 22Mg

25Mg

(5/2+)

0.10 25Mg 25

Mg 24Mg 24

core 24Mg 24Mg 23Mg26Mg

(0+)

0.11 26Mg 25

Mg 25Na

core 25Mg 24Mg 24Na

Use of a natural Mg targetUse of a natural Mg target

even-even odd-A odd-odd

22221212MgMg10(2)10(2)

24241212MgMg12(4)12(4)

T=0 T=0

Mg even-even core: Mg even-even core: 22,2422,24MgMg

Use of natural Mg target and Use of natural Mg target and identification of six identification of six hypernuclei hypernuclei

s, d

←d

27Al(K-,-)→ p+26

Mg (p gate)

23Na(K-,-)→23Na (s gate)

(1) Natural Mg (2) 27Al(3) 23Na

s,p

2323NaNa

2626MgMg

2424NaNa

10%10% 11%11%79%79%

2525MgMg2424

MgMg2323MgMg

s d

SummarySummary

• The sd-shell region more vast than the p-shell

• Importance of coupling of to nuclear collectivity (non-spherical vacuum) in the sd-shell – Core polarization effect of in the 2D (,) plane

• Measurement of the inter shell (p→s) ray

• -ray spectroscopy of 25Mg with a use of natural

target (Hyperball-J, SKSMinus, LaBr3/CsI detectors?)

• Essential role of coincidence technique in the sd-shell