1. T. Kishimoto RCNP and Physics Dept. Osaka University
Kaon-Nucleus Interaction Studied through the In-Flight (K-, N) Reaction
T. Kishimoto
RCNP and Physics Dept.
Osaka University
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2. K-nucleus interaction
Kaon condensation in neutron stars
Atomic X ray data: two solutions (Batty, Friedman, Gal)
deep ~180 MeV K-con (mK~2.5 r U)
shalow ~80 MeV no K-con
K- production in HI reaction: attractive
L(1405)
K- p X ray data
repulsive shift: (bound state L(1405)) strongly attractive
phenomenological potential (Akaishi Yamazaki)
Recent experiments: controversial
Kaonic nuclei
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3. in-flight (K-,N) reactions
TK, PRL83,4701, ’99
Elementary s K- n K
ds/dW(lab)=
(Pl/Pcm)2ds/dW(CM)
~10mb/sr
Initial and final wf, q ~ 0.3 GeV/c ~ pF
★Known mechanism (predictable cross section)
★Least background (pN~1.3GeV/c for pK~1 GeV/c)
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4. Exploratory Experiment at BNL
Bound region
Appreciable strength
unbound
16O(K-,n)
missing mass
@PK~0.93GeV/c
water target
Attractive K-nucleus
interaction
p(K-, n)K0
sum
Hyperon production
Potential depth ~200MeV
Cross sections: consistent
a KEKPS E548 -
M(15O+K-)
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5. KEK-PS E548 Study of Kaonic Nuclei by the (K- ,p) reaction
(K-,p) and (K-,n) reactions on
16O (water target)
12C (graphite and CH2 targets)
Improvements over BNL experiment
Proton (KURAMA spectrometer):
Neutron counter: ~20msr,
Decay counter (NaI array): ~0.5 of 4π
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6. Beam line and spectrometer
K2 beam line
pK=1 GeV/c (pN=1.2~1.3 GeV/c)
10k K- for 3Tp (~1/10 of BNL)
Trigger rate a ～500/spill
~1GK- on Target
Liquid scintillator
for Neutron counter
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7. Neuron counters Plastic scintillator array Conversion layer
2 layers of 5cm thick plastic
1.5m x 1.5m
Conversion layer
Liquid scintillator container
20cm thick 1.5m x 1.5m
Efficiency and time resolution
9.8m from the target p n
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8. Decay counter ・Charged particles ・Vertex points NaI 5x5 KURAMA NaI 3x4
Decay particle
FAC
VZH
20cm
BAC 1
BAC 2 LC BS
P or n
Target(water)
BQC
K- Beam 1.0 GeV/c
10.5cm CV
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VZH is to identify vertex to give neutron flight length

9. MM 12C(K-, n) Solid line: best fit Re(V)=-190MeV Im(V)=-40 MeV
multi.(decay)>=1
Solid line: best fit
Re(V)=-190MeV
Im(V)=-40 MeV
Dotted line:
Re(V)=-60 MeV
Im(V)=-60 MeV
Bound region
ds/dW mb/sr/10MeV
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-BE (MeV)

10. MM 12C(K-, p) Solid line: best fit Re(V)=-160MeV Im(V)=-50 MeV
multi.(decay)>=1
Solid line: best fit
Re(V)=-160MeV
Im(V)=-50 MeV
Dotted line: Chiral
Re(V)=-60 MeV
Im(V)=-60 MeV
Bound region
ds/dW mb/sr/10MeV
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-BE (MeV)

11. Potential depth by comparison with calculated spectra
Green function method
Consistent description of bound to unbound region with imaginary part (all final states)
J. Yamagata, S. Hirenzaki et al., PRC74
T. Hayakawa (PhD)
Quantitative comparison
Potential
Re(V)
Im(V(Eex))
Spectrum shape
Absolute cross section
Pion emission
energy dependence
Two nucleon
absorption
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12. c2 contour plot (K-, n) (K-, p) 60 MeV × Fit 1. whole region
2. bound region
Re(V)=-190 MeV
Im(V)=-40 MeV
(K-, n)
Im(V) MeV
Re(V)=-160 MeV
Im(V)=-50 MeV
(K-, p)
60 MeV　×
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Re(V) MeV

13. Effective nucleon number Neff
Neff= s(12C(K-, N))/ s(p(K-, N))
~1.5
calculation (40 mb for s(KN) and s(NN)
Neff(Eik)~1.27
Neff(Eik)~1.44 (with A-1 correction)
Background process
Fitting of -BE=100~200 MeV region
quadratic function
multi-step?
s~20 mb/sr
We are seeing
(K-, N) reaction
not backgrounds
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14. 16O(K-,p) and 16O(K-,n) Χ2(DOF=12) (-60,-60) O(K,n)X 束縛領域 Best fit
(-180,-40)
(-160,-40)
O(K,p)X 12
束縛領域
W(MeV)
ΔV≠0
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BG (multi-step…)
V(MeV)
-BE(MeV)

15. A and Isospin dependence
Assumption: attraction is from NI=0: I=0 (K- p, K0n)
pairs in kaonic nuclei.
NI=0
16O(K-,N) C(K-, N)
Isospin of
kaonic nuclei
I=0 (K-,n)
I=1 (K-,p)
(K-,n)
Potential depth ∝ NI=0/A
cal(MeV) obs(MeV)
12C(K-, n)
12C(K-, p) ~160
16O(K-, n) ~180
16O(K-, p) ~160
(K-, n)=((I=0)+(I=1))/2
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16. Summary Missing mass spectra of 12C(K-, N) indicate
12C (K-, n): Vr ~ 190MeV Vi ~ -40 MeV,
12C (K-, p): Vr ~ 160MeV Vi ~ -50 MeV,
Vr ~ 200 MeV a Kaon condensation
Isospin dependence may be consistent
12C results in PTP 118, 181 (2007)
16O(K-, N): same conclusion
paper in preparation
Future study at J-PARC
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