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NEUTRON-RICH HYPERNUCLEI ARE COMING. WHAT THEY TELL US ?

Lubom´r Ma jling i Nuclear Physics Institute, CAS z Re, Czech Republic Bogoliubov Laboratory of Theoretical Physics, JINR
E-mail: ma jling@ujf.cas.cz

OUTLINE 1. Nuclei with a Neutron Excess 2. - Hypernuclei 3. Neutron - Rich Hypernuclei 4.
6

H could be identified - so what ?

5. Outlook

1


1.

NUCLEI WITH A NEUTRON EXCESS

In the last twenty years a new main stream in nuclear physics, namely physics of nuclei in the vicinity of the neutron drip line has been constituted B. Jonson, Phys. Reports 389, 1 (2004). A number of spectacular effects have been observed: - a new type of clusterization, "neutron halo", - the N-Z dependence of NN interaction and shell occupancy, to mention a few. T he goals are clear : to identify the different phenomena, to develop and test proper models, to establish the foundation of these models.

Several generation facilities for the production and study of wide variety of exotic nuclei have been constructed around the world. Recently, the exploration of "exotic probes", was suggested. µ- and p, ¯

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The p otential of hyp ernuclear physics
Hypernuclei are nuclei with a hyperon replacing nucleon. In some sense, -hypernuclei are "radioactive" nuclei also their lifetime 2 · 10-10 s is governed by weak processes.
Some recent review: · O. Hashimoto and H. Tamura: Spectroscopy of hypernuclei Progr. Part. Nuc. Physics, 57, 564 (2006). · Topics in Strangeness Nuclear Physics, (Eds. P. Bydovsky, A. Gal, J. Mare) z ´ s Lecture Notes in Physics, 724, Springer, 2007. · T. Bressani: Hypernuclei: Perspectives of hypernuclear physics in this decade Proceedings of the International School of Physics "Enrico Fermi", Course 153, Varenna, Italy, IOS Press 2003. · Proceedings of the International School of Physics "Enrico Fermi", Course 158, Varenna, Italy, 2004, IOS Press 2005. Pro ceedings of the Int. Conference on Hypernuclear & Strange Particle Physics : · Torino, Italy, 23 ­ 27 October, 2000 Nuclear Physics A 691 (2001) (Edited by E. Botta, T. Bressani and A. Feliciello). · Newport News, VA, USA, 14 ­ 18 October, 2003 Nuclear Physics A 754 (2005) (Edited by A. Gal and E. Hungerford). · Mainz, Germany, 10 ­ 14 October 2006 The European Physical Journal A (2007) in press.

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.

Motto

As our experimental and theoretical tools are sharpened, we proceed to build structure on top of foundations previously constructed. Much of what we do was anticipated by our predecessors.
.

.

Ed Hungerford, Summary of HYP2006

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2.

- HYPERNUCLEI
9

Chart of light nuclei and hyp ernuclei

C

10

C B

11 10 10

C C B

12 11 11 10 10 9 9 8

C C B B

13 12 12 11

C C B B

14 13

C C B B

15 14 14 13

C C B B

2141 9

C B

9
3580 8

13 12

1p

185

7

Be 8 Be 9 Be Be Li Li
8 7
92

Be 11 Be 12Be 13 Be
10

Z

1370 7

Be Li Li

Be 11 Be 12 Be
1n 11

6
4 3

7
1690 6

Li Li

10 9

Li Li

Li

12

25

11 2n

Li Li

He 5 He 6 He 7 He 8 He 9 He 10He 11 He He 4He 798 6He 445 8 He 100 1069
2n 6 4n 8

3 1

H

2

H 4H H 3H

H

H

3190 1700 2700

840

-N

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B values of light hyp ernuclei
B 12 10 8
8 He 9 Li

15 N

+

12 B 11 B 12 C

+

+

+

13 C

+

14 C

+

10 Be 10 B

++
#

++

+

8 Li

6 4
4 He 5 He

+8+ + Be

9B 9 Be

7 Li 7 He 7 Be 6 He

+

+

+ ++

6 Li

2
3H

+ 4 + 3

+

+

H

4

5

6

7

8

9

10

11

12

13

14

15 A

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Sp ectroscopy of

- hyp ernuclei

Systematic studies of hypernuclei began with the advent of separated kaon beams which permitted the use of counter technique. The level structure of primary hypernuclei is experimentally studied. There are two one-step direct reactions of such a type: 1:
A A

n e u t ro n Z (K - , - ) A Z Z ( + , K + ) A Z p ro t o n
A A

Chrien, Dover,

ARNPS 39, 113 '89,

and

Hagesawa et al., PR C 53, 1210 '96.

2:

Z (K - , 0) A(Z-1) Ahmed et al., PR C 68, 064004 '03, Z (e, e K +) A(Z-1) Miyoshi et al., PRL 90, 232502 '03,
Y u a n e t a l., PR C 73, 044607 '06, Iodice et al., PRL 99, 052501 '07.

and

.

.

Recently, Tamura constructed a large acceptance Ge detector array dedicated to hyp ernuclear gamma-ray sp ectroscopy

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S p e c t ra o f

- hyp ernuclei

A schematic representation of the decays of en excited hypernucleus showing the decay of highly excited states by Auger and transitions.

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Example

Hypernuclear mass spectrum of 7 Li obtained in ( +, K +).

Level scheme of the 7 Li bound states.
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.

D o u b le t s p lit t in g

2S +1

LJ

+

1 2

E

+

·



2S +1

LJ Z

E

c 2S +1

A-1

LJ Z

-

1 2

A

E

-

·

core

hypernucleus

Contributions from the spin-dependent components of the effective N interaction to the ( 1+, 0+ ) doublet splitting core doublet
2 5

interaction S T 1 1 16 7 -8 21 40 3 2

S

1 2 1 2 1 2

(3S1,1 S0) (5D1 ,5 D0 ) (3 P1 ,3 P0 )

D P

-

3

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Phenomenological N interaction

V

N

(r) = V0(r) + V (r) sN s + V lN s + VN (r) lN sN + VT (r) S1 S SN T

2

APPROACH free NN + SU
flavor

(3)

+

limited YN



free YN model
effective N interaction
SHELL MODEL

Nijmegen

M il le n e r



EXPERIMENTAL DATA Hypernuclear transitions
7

Li :5,

9

Be : 2 ,

13

C :1,

16

O :2

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RESULT: VN radial integrals Veff GSD MGDD Millener + N
7 9

0 0 0 0 0 0 0 0 0 0 0 . . . . . . . . . . . 1 5 5 4 4 4 6 5 5 5 4 5 0 0 32 8 3 1 5 5 2 6 0 0 9 7 0 1 8

S 0.57 -0.04 -0.04 -0.010 -0 -0 -0 -0 -0 -0 -0 . . . . . . . 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 5 3 3 2 1 1

SN -0 -0 -0 -0 -0 -0 -0 -0 -0 -0 -0 . . . . . . . . . . . 2 0 4 3 4 3 5 5 5 4 3 1 8 7 90 3 9 4 4 0 6 5 0 0 9 9 8 1 4 0 0 0 0 0 0 0 0 0 0 0

T . . . . . . . . . . . 0 0 0 0 0 0 0 0 0 0 0 0 4 4 28 2 3 2 3 2 2 3 1 0 9 8 5 3 0

year 1 1 2 2 2 2 2 2 2 2 2 9 9 0 0 0 0 0 0 0 0 0 7 8 0 0 0 0 0 0 0 0 0 8 5 1 5 1 6 1 3 1 1 3

Li

Be C O

13 16

GSD: MGDD: + N :

Gal, Soper and Dalitz, AP 113 Millener, Gal, Dover and Dalitz, PR C 31 Millener, NP A 754

Millener: Millener, NP A 691

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3.

NEUTRON - RICH HYPERNUCLEI

The one problem is difficulty of making a neutron-rich hypernucleus, the other is to identify it from its decay modes. 3.1 DIRECT PRODUCTION The strangeness and double charge exchange (S&DCX) reactions (K - , + ) : or ( - , K + ) : ( - + p ) + p K + + (- + p ) n+ +K
+

( K - + p ) + p + ( 0 + p ) + n +
+

open way to the production of neutron-rich hyp ernuclei.

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The status of exp erimental efforts Hypernuclei Production in S&DCX Reactions Reaction
- ( K st , + )

year

6

H

7

H

9

He

10

Li

12

Be

16

C

Formation probability per stopped K -, (â105)

KEK FINUDA ( - , K + )

1996 < 23 2006 < 2.5 < 4.5 1 1 . 3± 1 . 9 22
Lanskoy, nucl-th/0411004

< 6.1 < 2.1

< 6.2

Cross section d /d [ NANO barn / sr], (p = 1.2 GeV/c)

KEK 2005 calculation 2004
calculation:

7 2.5

Cross sections of the two-steps ( -, K +) reaction are smaller by three orders of magnitude than those of one-step ( +, K +) reaction.

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Published results A. KEK Missing mass spectrum of the ( -, K +) reaction on 10B target. P.K. Saha, T. Fukuda et al. PRL 94 ('05) 052502

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B. FINUDA Collab oration Search for 6 H and 7 H with the (Ks-op, +) reaction t M. Agnello, ... T. Bressani, ... B. Dalone ... PL B 640 ('06) 145

So, we have not only upper limits for reactions with stopped kaons, but even first p ositive results for ( -, K +) reaction.
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3.2 NEUTRON - RICH

HYPERFRAGMENTS

Tamura discussed formation of the neutron-rich hyp erfragments from stopped K - absorption. But it is a problem how to identify hyperfragment species and enhance a signal to the background ratio. There is one peculiar case where both problems are manageable: experiments with relativistic hypernuclei. The new accelerator Nuclotron at Dubna together with a new "GIBS - NIS" spectrometer offer new possibilities of carrying out hypernuclear experiments.

The scheme of the experiment: S, C PC
1,2

T is target; M is magnet;

are trigger counters; V is vacuum decay volume; are proportional chambers.
17

1-4


Identification To DISCRIMINATE the MASS value of the isotopes of the hypernuclear daughter nuclei one should measure the corresponding momenta. The momentum values of 3He, 4He and 6He are concentrated in the 14 GeV/c, 19 GeV/c and 29 GeV/c bands. Such difference can be measured easily to separate three possible reactions of the hydrogen hypernuclei production and decay in the 7Li beam:
Momenta of daughter nuclei
number of events 2500
3

Entries

60000

2000

He

4

He
6

He

1500

1000

500

0

14

16

18

20

22

24

26

28

30

32 P (GeV/c)

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Exp ected yields beam
3 4

target + + +
12 12

production
3 4 3

decay
3 4 3 6 4 3

N
- - - - - -

He He Li

C C C

H + ··· H + ··· H + ··· H + ··· H + ··· H + ···

He + He + He + He + He + He +

100 600 400

7

12

6 4 3

HYDROGEN HYPERNUCLEI CAN BE UNAMBIGUOUSLY IDENTIFIED

We note that ALL Hydrogen hypernuclei are produced. The 3 H and 4 H can be used as a reference sample to confirm production of 6 H.

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Source of hyp erfragments

ss1

Q AQ s Q A A A U A

H+p Eth = 24 MeV H + 3H Eth = 15 MeV
4

6

pp1

sp1

He + Eth = 5.2 MeV 5 He + nn Eth = 3.2 MeV
7

6

7

Li

He

hyperfragment

Decay channels of the 7 He hypernucleus. The neutron, proton and are marked by ·, , and , respectively.
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4.

6

H COULD BE IDENTIFIED - SO WHAT ?

CHAIN of four (hyper) nuclei with two neutron "halo" ENERGY SPECTRA

E, MeV]

/// 2 ////
+1.7 0 -2 -4
3

5+ 2 1+ 2

3

H + + n2
4 4

////2 He + n
- 0.97
2

+

4

He + + n

2

H + n2

H+n
- 4.1

2

0+
5

He + n

2

0

+

5+ +2 3 2

- 5.23
5

1+ 2

H

6

H

6

He

7

He

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.

Model description

.

Such a unique comparison could shed light on a limit of three-body model (core + n + n) as well as on the role of continuum.

A proper shell model description of loosely bound nuclei should take into account the coupling of the discrete bound states with the continuum of scattering states. The tool of choice is Gamow shell model :

N.Michel, W.Nazarewicz, M.Plosza jczak and J.Okolowicz: Gamow shel l model description of weakly bound nuclei and unbound nuclear states Phys. Rev. C 67 (2003) 054311

and / or

the continuum shell mo del : Continuum Shel l Model

A. Volya, V. Zelevinsky:

Phys. Rev. C 74 (2006) 064314

in which both continuum effects and correlations between nucleons are taken into account simultaneously.
.

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.

Neutron rich Hydrogen

What does it happen if one proton is added in the six neutron system?
S. Aoyama, FINUSTAR 2

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5.

OUTLOOK
8

The setup at JINR Dubna could identify

H also ­ if it exists.

It is a great challenge to produce such a neutron-rich hypernucleus.
3.1 1.8 0
+

///

2+

///

2+ 0+ 0+

4He
ss

6 He
ss

8 He
ss

1

] 4 He : 1+ 0
+

1

4

6

4H

6H

] 6 He : 1+ 0+

1

] 8 He : 1+ 0+

8

8H

N =2 Z

N =4 Z

N =6 Z

Spectra of the low lying levels in 4 He, 6 He and 8He nuclei and doublet splitting in 4 H, 6 H and 8 H hypernuclei.

So, we obtain chain of three hypernuclei with a similar (and very simple ! ) ground state doublet.

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GIBS - NIS Collab oration : S. Afanasiev, V. Aksinenko, Yu. Anisimov, S. Avramenko, V. Balandin, Yu. Batusov, S. Bazylev, Yu. Belikov, Yu. Borzunov, Yu. Chencov, L. Golovanov, A. Golokhvastov, A. Isupov, A. Ivanov, Yu. Ivanov, A. Kovalenko, A.Litvinenko, J.Lukstins, V.Lysyakov, A.Malakhov, P.Manyakov, E.Matyushevskiy, V.Matyushin, I.Migulina, G.Nikoloyevskiy, O. Okhrimenko, A. Parfenov, N. Parfenova, V. Peresedov, S. Plyaskevich, A. Povtoreiko, P. Rukoyatkin, R. Salmin, V. Tereschenko, I. Yudin, JINR, Dubna, D. Chren, T. Horadovsky, Z. Kohout, O. Ma jlingov´, M. Solar, B. Sopko, z ´ a FME CTU, Prague, C. Granja, S. Posp´il, V. Sopko, is IAEP CTU, Prague, L. Ma jling, z INP CAS, Re

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