Transcript PowerPoint プレゼンテーション

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
p
• Comparison with
model calculations
• Summary
“deep-hole”
nucleus
＋
Production of the double- & twin- hypernuclei
• Observed events in KEK-E176/E373 (hybrid-emulsion
method)
 12
10
9
4
  C  Be  t or  Be   H
or
6

He    t
4

H  t 
 12 C9 Li   : largest Q - value
Two ’s easily stick to the nucleus for the s-proton substitutional state
  p      28 MeV  Esep (s - nucleon)

+
‘p’


 + “ p” →  + 
 12 C11 B* (s - hole)    
+
+
SU(3)-model calculation
Yamada et al., PRC53(1996)752
(microscopic cluster model)
distribute quanta N in (f1,f2,f3)
N   (2ni  li )
i
f1 SU(3)(l,m)
f2
l=f1- f2
f3
m=f2- f3
relative w.f.
(lm)=(40)
Assume the SU(3)(l,m) of
11B(s-hole) is the same as
that of 12C
suppression of -decay !
(lm)=(50)
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↑）
(-decay is suppressed by the spatial SU(3) symmetry)
v.s. Statistical decay （G↓）
(-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.
11B(s-hole)
•
11B(s-hole):
low threshold of 3-body decay
• 15N(s-hole) is better for the
comparison with theoretical
models
and
15N(s-hole)
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
(E148 exp.)
(E110 exp.)
(p,2p) coincidence spectra
Excitation of hole states in11B via 12C(p,2p) reaction
Excitation spectra of 11B and 15N
(without and with decay coincidence)
(E110)
Decay of
11B(s-hole) state
•
11B*
→ 10Be + p
→ 9Be + d
→ 8Be + t
→ 7Li + 
• “2-body decay” region
Ex(res)
< Max(5 MeV, Eth(3-body))
Decay of 15N(s-hole) state
• “2-body decay” region
Ex(res) < Max(8 MeV, Eth(3-body))
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
・ t-decay：
dominant
・ -decay：
large sequential
decay or 3-body decay
・ p-decay / d -decay：
oposite between
Exp. and CASCADE cal.
hatched region : “2-body decay” region
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
・ t-decay > -decay
Q(t-decay) < Q(-decay)
・ n-decay、 p-decay :
large sequential decay
(and/or 3-body decay)
・ n-, p-, d-decay :
similar pattern between
Exp. and CASCADE cal.
hatched region : “2-body decay” region
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
d 3
 d 
2

  F ( E; Ei , Gi ) Si
d1d 2 dE  d  NN i
Ei : i - th stateenergy, Gi  Gni  Gpi  Gdi  Gti  Gi : i - th width
Si2 : spectroscopic factor, F : Lorentzianfunction
• Partial width of 2-body decay: separation energy method
Gcl  2 Pl (kc ac ) l2 (ac )
Pl (kc ac )  kc ac /(Gl2  Fl 2 ) : penetration factor
 l2 (ac ) : reduced width
Substructures of the s-hole states in 11B and 15N
（comparison with the shell model calculations）
Fitting with BG + Peaks (asymmetric Lorentzian shape)
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 (++t) ?
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
Decay pattern for the outside
of “2-body decay” regions
Similar pattern !
Direct decay parts in the “2-body
decay” regions (Exp.- Casc./2)
G↑/ G↓～1.0
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 > -decay despite Q(t-decay) < Q(-decay)）
• 11B(s-hole) : large t-decay  S= -2 hypernuclear production via +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.
-ray emitted from the １5N(s-hole) state
• total branching ratio of decay to the excited states of the dughter nuclei : ~30%
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
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)
Particle identification with DE-E telescopes
( E  DE )1.73  E1.73
PI 
(arb. factor)
 (smallcorrection)
(thick : 100 mm)
(thin : 20 mm)
Important role of deexcitation -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 -ray
reduce background !
• 15 MeV -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*