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Experimental search for the
kaonic nuclei using the
d(π+, K +) reaction
Yudai Ichikawa
Kyoto University/JAEA
Progress on J-PARC hadron physics in 2014
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Inclusive analysis results
Coincidence analysis results
arXiv: 1411.6708
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Introduction (K-pp bound state)

Simplest kanoic nuclei, KNN (Total charge=+1, I=1/2) system
 B.E. and Γ strongly depend on the KN interaction.
 It is difficult to reproduce the experimental values.
K- + p + p ~ 2.37GeV/c2
T.Yamazaki et al.,
PRL 104, 132502 (2010)
Theoretical
value
Kbar-N interaction
Calculation
method
●
Chiral base
Variation
○
Chiral base
Faddeev
▲
Phenomenological
Variation
△
Phenomenological
Faddeev
M.Agnello et al., PRL 94, 212303 (2005)
3
J-PARC E27 experiment
( π+d→ K+X reaction at 1.69GeV/c)
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J-PARC
K1.8 beam line
+
K
K-pp
is produced
via a Λ(1405) doorway.
π+ + n → Λ(1405) + K+
Λ(1405) + p → K-pp
(→quasi free Λ* ）
π+
π+
Sks spectrometer
K+
K1.8 beam line
spectrometer
Y.Akaishi, T.Yamazaki, Phys. Rev. C 76 045201 (2007)
4
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RCA for B.G. suppression

There are a lot of B.G. of the quasi-free hyperon production.
 It is difficult to discuss the K−pp in the inclusive spectrum.
 Detect the proton(s) from the K−pp decay with Range Counter Array.


K−pp→Λ p→p π− p; K−pp→Σ0 p→p π− γ p; K−pp→Y π p→p π p + (etc.).
We suppress the quasi-free B.G. by tagging a proton or 2 protons.
0 K+ → p π- π0- K+
QF(B.G.): π+ “n”→
Λπ
K pp→ Λp→p π p
(proton spectator)
K+
Simulation
p
p
π+
RC-Seg3, 6
RC-Seg2, 5
RC-Seg1, 4
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Spectrometer performance (Calibration)
p(π+, K+)Σ+ at 1.58 GeV/c
The K+ momentum is same region
of the d(π+,K+)K-pp reaction.
Σ+
・ Missing mass resolution of Σ+
ΔM = 2.8 ± 0.1 MeV/c2(FWHM)
・ Missing mass resolution of the
d(π+, K+)X reaction
・ X = K-pp (B.E = 100MeV)
ΔM = 2.7 ± 0.1 MeV/c2(FWHM)
・ X = ΣN cusp (2.13 GeV/c2)
ΔM = 3.2 ± 0.2 MeV/c2(FWHM)
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p(π+, K+) at 1.69 GeV/c
Σ+
Σ(1385)+
M = 1381.1 ± 3.6 MeV/c2
Γ = 42 ± 13 MeV
PDG: M = 1382.8 ± 0.35 MeV/c2,
Γ = 36.07 ± 0.7 MeV
MMp [GeV/c2] 7
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d(π+, K+) at 1.69 GeV/c (Inclusive spectrum)
• There are a lot of B.G (quasi-free hyperon production).
2
Y* peak; data = 2400.6 ± 0.5(stat.)
±
0.6(syst.)
MeV/c
→It is difficult to identify+2.8
the K-pp from inclusive
spectrum.
2
simstructure
= 2433.0
-1.6 (syst.) MeV/c
• The overall
was understood
with
a simulation
+2.9
－32.4
± 0.5(stat.)-1.7 (syst.) MeV/c2
except“shift”
for two =
peculiar
deviations.
• ΣN cusp (~2.13 GeV/c2) and Y* peak postion
Quasi-free B.G.
- Λ, Σ+/0,
- Y*: Λ(1405),
Σ(1385)+/0,
- Λπ, Σπ
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d(π+, K+) at 1.69 GeV/c (Inclusive spectrum)


Forward scattering angle (θpiK(Lab) = 2-8°) was selected.
A cusp at ΣN threshold is prominent in the figure.
M0 = 2130.5 ± 0.4 (stat.) ± 0.9 (syst.) MeV/c2
+0.6
Γ = 5.3 +1.4
(stat.)
−1.2
−0.3 (syst.) MeV

This is the first observation in the inclusive measurement of this
reaction.
2
M(Σ0)+M(p)
= 2.1309GeV/c
Further detailed studies
including
the
present
data
M(Σ+)+M(n) = 2.1289GeV/c2
would reveal the ΣN-ΛN coupling strength and pole position.
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1 proton coincidence analysis



RC Seg2, 5 are free from the QF backgrounds.
Excess due to ΣN cusp is clearly observed ~ 2.13GeV/c2.
Broad Enhancement is observed around 2.3GeV/c2.

A possible explanation of the observed structure is the K-pp.
1p coin
/ Inclusive
ΣN
Cusp
K-pp?
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2 proton coincidence analysis


2 protons coincidence spectrums show the same tendency as
1proton coincidence spectrum.
We divided the 3 regions at the missing mass spectrum.
①MM<2.22GeV, ②2.22<MM<2.35GeV, ③MM>2.35GeV
Cusp region
K-pp region
Y* region
ΣN
Cusp
2p coin
/ Inclusive
K-pp?
①
②
③
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d(π+,K+pp)X spectra (Final state determination)
2p coin events
<Detection efficiencies of 2p>
Λp
Σ0 p
Yπp
Final states are known from
2p coincidence events.
MMd [GeV/c2]
Σ0 p
＋ Data
ー X = π (F.S.:Λp)
ー X = πγ (F.S.:Σ0p)
ー X = 2π (F.S.:Yπp)
ー Sum
Λp
Λp
Σ0 p
Σ0 p
Λp
Yπp
Yπp
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“K-pp”-like structure


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The broad structure around 2.26 GeV/c2 have been observed in the Σ0p final
state events.
We fitted with a relativistic BW function smeared with the resolution.



Mass:
(BE:
)
Width:
This distribution can reproduce the 1p coincidence probability spectrum (pink).
Blue and red lines show the flat component and summed one.
Differential cross section of
π+d→K+W, W→Σ0p process
1p coincidence probability
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Summary
•
•
The inclusive missing-mass spectra of the d(π+, K+) reaction
at 1.69 GeV/c has been observed for the first time.
The overall structure was understood with a simple quasifree picture. However, there are two peculiar deviations.
•
•
•
The centroid of the broad bump structure in Y* region was shifted
+2.9
to low mass side, by －32.4 ± 0.5 (stat.)-1.7 (syst.) MeV/c2.
We observed the ΣN cusp in the inclusive spectrum for the first
time in this reaction.
The double differential cross section of each final state was
estimated from 2p coincidence events.
•
We have observed a clear bump structure which corresponds to
“K-pp”-like structure in Σ0p final state events.

Mass:
(BE:
 Width:
)
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J-PARC E27 Collaboration
T. Nagae, H. C. Bhang, S. Bufalino, H. Ekawa, P. Evtoukhovitch,
A. Feliciello, H. Fujioka, S. Hasegawa, S. Hayakawa, R. Honda,
K. Hosomi, Y. Ichikawa, K. Imai, S. Ishimoto, C. W. Joo,
S. Kanatsuki, R. Kiuchi, T. Koike, H. Kumawat, Y. Matsumoto,
K. Miwa, M. Moritsu, M. Naruki, M. Niiyama, Y. Nozawa, R. Ota,
A. Sakaguchi, H. Sako, V. Samoilov, S. Sato, K. Shirotori,
H. Sugimura, S. Suzuki, T. Takahashi, T. N. Takahashi, H.
Tamura, T. Tanaka, K. Tanida, A. O. Tokiyasu, Z. Tsamalaidze,
B. J. Roy, M. Ukai, T. O. Yamamoto and S. B. Yang
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