A search for deeply bound kaonic nuclear states by

ストレンジネスとエキゾティクス・理論の課題
March 1-3 2007 Toba
A search for deeply bound
kaonic nuclear states
by in-flight 3He(K-,n) reaction
Hiroaki Ohnishi
RIKEN
For the J-PARC E15 collaboration
A search for deeply bound
kaonic nuclear states
Goal for the experiment J-PARC E15
 To answering the basic question
: whether the deeply bound state really exists?
 Direct production of K-pp cluster via 3He(K-,n) reaction

K-
3He
reaction
Decay?
???
K-pp
cluster
neutron
Possible K-pp decay mode
2370 MeV
2275 MeV
2267 MeV
K-pp
p+S-p
p-S+p
fit region
Phys. Rev. Lett. 94
, 212303 (2005)
FINUDA
Dominant
Decay mode
= YN
2054 MeV
cluster
B.E. = 115 MeV
L p decay mode
p
L
p2131 MeV
K-pp
S0 p
p
Lp
Invariant mass
reconstruction
S0 p decay mode
g
p
p-
L
p
Formation of K-pp via 3He(K-,n) reaction
3He
K-
reaction
Only charged particles
in final state
L
pp
K-pp
cluster
neutron
decay
p
This mode allows us to investigate
K-pp cluster with both
missing mass and invariant mass
spectroscopy
Detector concept
• Missing mass spectroscopy with forward going neutron
K- beam momentum used
1 GeV/c
for the experiment
In the case, if B.E. = 100 MeV
( FINUDA case)
Momentum of outgoing neutron
will be 1.3 GeV
• Bound state tagging with the measurement of decay product
– Good charged particle detection efficiency
– Good charged particle momentum resolution
L reconstruction will be crucial for this measurement
E15 Detector
Experiment will be performed at
K1.8BR beam line.
Neutron counter
Cylindrical detector system
GEANT4 detector simulation
Proton
Proton
K-
p-
B.E. = 100 MeV
Expected detector performance
L p decay mode
p
L
pp
• Expected decay mode for K-pp
S0 p decay mode
g
p
p-
L
p
∑ channel
Λ channel
– K-pp ➾ Λp ➾ pπ-p
– K-pp ➾ S0p ➾ gΛp ➾ g pπ-p
• Assume GK-pp= 60 MeV
Invariant mass of Λp (MeV)
Possible K-pp decay mode(2)
Back to the beginning
2370 MeV
K-pp
Akaishi-Yamazaki prediction
based on L(1405) as KN bound state
In this case,
K-pp can be decay to
2275 MeV
2267 MeV
pS mode
p+S-p
p-S+p
p 0 S0 p
Hyperon
production p+S0n
Y.Akaishi & T.Yamazaki,
PLB 535(2002) 70.
2131 MeV
S0 p
p +S -p
p 0 S +p
p -S +p
YN mode
S0 p
+
Lp
Question
1) Can we identify K-pp bound state only from missing mass?
2) How to tag formation of K-pp bound state via decay product?
2054 MeV
Lp
BR( K-pp → pSp)
= ???
BR( K-pp → YN)
Concerning on the decay mode of
K-pp →pSp
K-pp decay mode
pS mode
p 0 S0 p
p-S+p
p- p+n p
p +S 0 n
p +S - p
p0S+p
p -S + p
n from S decay
p
n
p-
n from
S decay
p+
p-
n
proton cannot
escape from target
p+
• Can we use p+p- from target region as a tag of pS decay ?
Still need to investigate
Summary
• J-PARC E15 experiment
– Search for simplest deeply bound kaonic
nuclear state, K-pp bound state
via 3He(K-,n) reaction
• Detector construction is in progress
• Experiment will be ready before Dec. 2008
L p decay modeΛ
p
L
p-
p-
p
S0 p decay mode
K-pp state
g
p
σ（MeV）
σ（MeV）
Expected detector performance
L
p
Λ momentum (MeV/c)
• Expected decay mode for K-pp
momentum (MeV/c)
∑ channel
Λ channel
– K-pp ➾ Λp ➾ pπ-p
– K-pp ➾ S0p ➾ gΛp ➾ g pπ-p
• Assume GK-pp= 60 MeV
Invariant mass of Λp (MeV)

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