1. Structures and decay of deep-hole states in light nuclei populated
5/9/2003 NSRT03
Structures and decay of deep-hole
states in light nuclei populated
by the (p,2p) reactions
Kyoto Univ. M. Yosoi
Motivation and purpose
Experiment and
results
Comparison with
model calculations
Summary
“deep-hole” p
nucleus ＋

2. Production of the double- & twin-L hypernuclei
Observed events in KEK-E176/E373 (hybrid-emulsion method)
Two L’s easily stick to the nucleus for the s-proton substitutional state + L +
‘p’ L X- +
X- + “ p” → L + L

3. SU(3)-model calculation
distribute quanta N in (f1,f2,f3)
Yamada et al., PRC53(1996)752
(microscopic cluster model)
SU(3)(l,m) f1 f2
l=f1- f2
m=f2- f3 f3
relative w.f.
(lm)=(40)
Assume the SU(3)(l,m) of 11B(s-hole) is the same as
that of 12C
(lm)=(50)
suppression of a-decay !

4. Motivation and purpose
Nuclear deep-hole state
　　Excitation energies, widths ： studied by (p,2p), (e,e’p)
　　their microscopic structures and decay： unknown
Decay processes in light nuclei
　　Direct decay from the doorway s-hole （G↑）
　　(a-decay is suppressed by the spatial SU(3) symmetry)
　　 v.s. 　Statistical decay （G↓）
　　(a-decay is preferable with its large Q-value）
　　mean free pass (L) ~ radius (R) for light nuclei
Related topics
　　Hypernuclear production (in particular, S=-2 system)
　　Astro-particle physics : nucleon decay, n-detection, etc.

5. 11B(s-hole) and 15N(s-hole)
low threshold of 3-body decay
15N(s-hole) is better for the
comparison with theoretical
models

6. Experiment(E110/E148) Hole states : (p,2p) reaction
at 392 MeV using GR and LAS
(~0 MeV/c recoil momentum for the
center of s-hole states)
Decay charged particles :
DE-E SSD telescopes (16 sets)
(DE: 20,50 or 100mm, E: 5mm)
Thin targets : C(0.5mg/cm2)
SiO2 & Si (2mg/cm2)
Decay neutrons : Ice (H2O) target
Liquid scintillator array
(E110 exp.)
(E148 exp.)

7. (p,2p) coincidence spectra
Excitation of hole states in11B via 12C(p,2p) reaction

8. Excitation spectra of 11B and 15N (without and with decay coincidence)

9. Decay of 11B(s-hole) state
11B* → 10Be + p → 9Be + d → 8Be + t → 7Li + a
“2-body decay” region
Ex(res)
< Max(5 MeV, Eth(3-body))

10. Decay of 15N(s-hole) state
“2-body decay” region
Ex(res) < Max(8 MeV, Eth(3-body))

11. Decay branching ratio of the 11B(s-hole) comparison with the statistical model (CASCADE cal.)
Level density : low lying discrete states ←　data table
highly excited states ←　parameters (a, d)
( back-shifted Fermi-gas)
Transmission coefficients ←　global OMP
　hatched region : “2-body decay” region
・ t-decay：
dominant
・ a-decay：
　large sequential
decay or 3-body decay
・ p-decay / d -decay：
oposite between
Exp. and CASCADE cal.

12. Decay branching ratio of the 15N(s-hole) comparison with the statistical model (CASCADE cal.)
Level density : low lying discrete states ←　data table
highly excited states ←　parameters (a, d)
Transmission coefficients ←　global OMP
　hatched region : “2-body decay” region
・ t-decay > a-decay
Q(t-decay) < Q(a-decay)
・ n-decay、 p-decay :
large sequential decay
(and/or 3-body decay)
・ n-, p-, d-decay :
similar pattern between
Exp. and CASCADE cal.

13. Shell model calculation (Yamada, NPA687(2001)297c)
Model space : 1hw shell model
Interaction: Cohen-Kurath (p-shell)
+Millener-Kurath (p-sd, s-1-p shell)
+ G-marix (Reid soft-core or Bonn)
Excitation energy spectrum for (p,2p) reaction: DWIA
Partial width of 2-body decay: separation energy method

14. Substructures of the s-hole states in 11B and 15N （comparison with the shell model calculations）
Fitting with BG + Peaks (asymmetric Lorentzian shape)

15. Comparison with the SU(3)-model&shell-model (11B(s-hole)　“2-body decay” region)
Decay pattern of the higher excitation region is similar to that of the SU(3)[443](04) state
Shell model does not explain large t-decay
Need to include the 3-body decay channel (a+a+t) ?

16. Comparison with the SU(3)-model&shell-model (15N(s-hole)　“2-body decay” region)
Shell model cal. agrees with the experimental decay pattern.
（but excitation energy should be shifted anbout 5 MeV ）
SU(3)-model : large d-decay

17. Decay pattern for the outside of “2-body decay” regions
Direct decay parts in the “2-body decay” regions (Exp.- Casc./2)
G↑/ G↓～1.0
Similar pattern !

18. Summary
Experiment
Measure decay particles from the s-hole states in 11B,15N excited by the 12C,16O(p,2p) reactions.
　　　（Ep=392 MeV、GR and LAS、SSD-Ball、n-detectors）
Structures of the 11B(s-hole) and 15N(s-hole)
s-hole states : 3~4 sub-bump-structures in both cases.
 qualitatively explained by the recent shell model calculation.
Fragmentation of the s-hole state
Experimentally prove the selection rule from the spatial SU(3) symmetry in the “2-body decay” regions.
　　　（t-decay > a-decay despite Q(t-decay) < Q(a-decay)）
11B(s-hole) : large t-decay  S= -2 hypernuclear production via X-+12C
　　No theoretical models explain experimental decay pattern quantitatively.
15N(s-hole) : G ↑/ G ↓~1.0 is deduced from the comparison between the experimental results and statistical- and sell-model calculations.
g-ray emitted from the １5N(s-hole) state
total branching ratio of decay to the excited states of the dughter nuclei : ~30%

19. Collaborators (RCNP-E110/E148)
Kyoto U. : H.Sakaguchi, M.Nakamura, H.Takeda, T.Taki,
N.Tsukahara, M.Uchida, Y.Yasuda, M.Yosoi
RCNP : M.Fujiwara, H.Sakemi, H.Fujimura, M.Itoh,
H.P.Yoshida, E.Obayashi, K.Hara, A.Tamii,
I.Daito, R.G.T.Zegers
Konan U. : H.Akimune, K.Yamasaki-Hara
CNS, U. of Tokyo : T.Kawabata
LNS, Tohoku U. : T.Ishikawa
Kyushu U. : T.Noro
Kantogakuin U. : T.Yamada
Spring-8 : H.Toyokawa, H.Ejiri
ICR, U. of Tokyo : Y.Itow, M.Shiozawa, K.Kobayashi

20. Angular correlation (recoil momentum distribution ) for the 16O(p,2p)15N(s-hole) reaction
Fitting with DWIA+constant BG
　　　　　(multi-step, (p,3p), etc.)
BG: ~15% at qLAS= 51°
1st bump (16-20 MeV):
also consistent with s-hole
Spectroscopic factor : ~1.6
(16 ≦Ex ≦40 MeV)
(BG: ~10% for the
12C(p,2p)11B(s-hole) reaction)

21. Particle identification with DE-E telescopes
(thick : 100 mm) 　　　　(thin : 20 mm)

22. Important role of deexcitation g-rays from the 15N hole states
(nucleon decay search with water Cerenkov detectors)
Ejiri, PRC48(93)1442
p →n K+ , K+ →m+n
m (236 MeV) + prompt g-ray
reduce background !
15 MeV g-ray from 12C, 13C or 13N
after particle decay of 15N ,15O(s-hole)
n → nnn etc.
neutral current n-detection
n +16O → n’+ p + 15N*