Search for the K-pp bound state
via photon-induced reaction
“Hadron in nucleus” @ Kyoto University 1st. Nov. 2013
A. O. Tokiyasu (RCNP) for LEPS collaboration
ContentsWhat are Kaonic nuclei?
LEPS experiment at SPring-8
Results
Future work: search in LEPS2 experiment
Conclusion ☆ This presentation is based on arXiv.1306.5320
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What are Kaonic nuclei?
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Kaonic nuclei KN interaction is strongly attractive (I=0) K bound state in nucleus → Kaonic nuclei
important to understand the sub-threshold KN interaction
KNN bound states are the simplest kaonic nuclei. K-pp bound state: largest B.E.
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KN L(1405) (KN + Sp)
CERN, LEPS, CLAS
KNN wide peak structure
FINUDA, DISTO
KNNN no narrow peak KEK PS-E471/E549
K + nucleus Kaon potential Osaka Group (KEK, BNL)
T. Yamazaki et al. PRC76, 045201
A.N. Ivanov, et al.arXiv:0512037v2
N. V. Shevchenko, et al. PRC76, 044004
Y. Ikeda et al. PRC76, 035203
A.Dote, et al.NPA804, 197
S. Wycech et al.PRC80, 045207
M. Bayar et al.arXiv:1207.1661v1
B.E. [MeV]
48 118 50~70 60~95 20±3 56.5~78
15~30
G[MeV]
61 58 ~100 45~80 40~70 39~60 75~80
K-pp bound state
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B.E = 10- 95 MeVG = 39 – 100 MeVdepending on- KN interaction- calculation methods
Hadron in nucleus @ Kyoto University
)()( syststat 34
65115
)()( syststat 23
141167
)()( syststat 53103 )()( syststat 108118
B.E. =B.E. =G =G =
MeVMeV
MeVMeV
Theoretical prediction
Experiment
PRL 94, 212303 (2005) PRL 104, 132502 (2010)FINUDA @ DAFNE DISTO@ SATURNE
stopped K-
Lp invariant mass
↓ inconsistent↓
pp→K+LpMM(K+)
search experiments via different reactions are awaited! → photon-induced reaction.
g-induced reaction
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K+
p
g
K-, K*-
pn
detect K+ at very forward angle→ t-channel reaction (on-shell meson exchange)→ virtual K- or K* beam ( p = 06-1.0 GeV/c)g (J=1, I=0, 1 )
N
NK
d (g, K+ p) X Eg=1.5- 2.4 GeV
p- X=K-pp ←This talk
p0 X=K-pn p+ X=K-nn
search for the peak structure in the inclusive missing mass spectrum MMd(K+p-)
search region: 2.22 – 2.36 GeV/c2
B.E. = 10 – 150 MeV
Hadron in nucleus @ Kyoto University
HADRON13(g, K+) K-pn(g, K+p+) K-nn
E, p measured
LEPS experiment at SPring-8
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LEPS/SPring-8
Data take:2002/2003, 2006/2007 7.6 x 1012 photonss LD2 target (Total)
SPring-8: 8 GeV electron storage ringLEPS : hadron physics using g beam
Backword Compton Scattering
e
e
Detect withTagging counter
Eg=1.5 - 2.4 GeVexperimentalhatch
355nm laser
8 GeV
LEPS
DEg=12 MeV
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LEPS spectrometer
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TOF
Dipole Magnet 0.7 [Tesla]
Target
Start Counter DC2 DC3
DC1SVTX
AC(n=1.03)SSD(SVTX)Drift Chamber(DC 1~3)
position
Start Counter(SC)Time of flight wall(TOF)
time
Aerogel Cherencov counter(AC)Start Counter (SC)
trigger
g (1.52.4 GeV)
p-
K+
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K+ and p- are detected at very forward angle(< 15 degree)
particle identification
K+
p- Dp ~ 6 MeV/c @ 1 GeV/c
DM ~ 10 MeV/c2
(2.22 - 2.36 GeV/c2 ) in MMd(K+p-)
TOF (Time of flight)
m2 = p2(1/β2 - 1)
Track reconstruction + Runge-Kutta method.
p
p+
K-
0
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Analysis and Results
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missing mass spectrum
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→No peak structure was observed!
expected signal
A: g n → S- K+
S- → n p-
B: g p → L K+ p-
C: g p/n → S-/0 K+ p-
B+ C : ~11 mbPeak structure was searched in 2.22 - 2.36 GeV/c2.
A
B
C
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cut condition
-cosqlabK>0.95
-cosqlabp>0.95
-0.25<pK+<2.5-0.25<pp-<0.6
Determination of the upper limit of production cross section
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log Likelihood ratio method.
DlnL = logL[Signal + BG] - logL[BG]
Signal : Breit-Wigner (fixed B.E., G)BG : quasi-free processes (listed in Figure)
The yields : -2DlnL=3.84 → upper limit at 95 % C.L.
upper limit of cross section
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-G= 20 MeV 0.17 - 0.55 mb
-G = 60 MeV 0.55 - 1.7 mb
-G =100 MeV 1.1 – 2.9 mb
1.5 - 26 % of YKp production cross section.
B.E. 15 points (10-150 MeV)G 3 points (20, 60 and 100MeV)
Hadron in nucleus @ Kyoto University
Background processes
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MMp(K+p-) and Mp(K) spectra were fitted simultaneously.Fitting function: quasi-free process gNY K+p
- gNY* K+
gNYp K+p
Main component:gp L(1520) K+
(~20%) → Sp → N pg N Y p K+ p
(~20%)
MMp(K+p-)
MMp(K+)
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Search in LEPS-2 experiment
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LEP2 facility
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acceptance: 5 -120 degree (charged particle)30 - 100 degree (g)p/Dp ~ 1%
beam intensity x10 of LEPS ( 107 cps)
4 p detector under construction for
the 1st experiment
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LEPS 2-1 Exclusive search by tagging two protons
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accepted in LEPS2
Main Back ground process: quasi-free process (one nucleon is spectator)
To improvement of S/N: Non-mesonic decay modetwo high momentum proton
Tag
g d K+ + p- + K-
pp K-pp L + proton(p1) L proton (p2) + p-
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Toy MC
Toy MC
accepted in LEPS2
LEPS 2 – 2 Search in the g+d→Ks L p
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g+d→ Ks + K-ppK-pp → L + pー Ks (L) pー Ks L (p)ー (Ks) L pー Ks L p( ) ← ID with missing mass
g + d → Ks + K-ppK-pp → S0 + pS0 → L + g (50140 MeV) ← detectable
We can measure the B.R. (Lp/S0p)
Dalitz plot in the Center Mass system
K-pp production(B.E. = 60 MeV = 80 MeV = 100 MeV = 120 MeV)
Toy MC
Conclusion
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Conclusion
K-pp bound state give us rich information on the sub-threshold KN
interaction. K-pp bound state was searched for via the g d
K+ p- X reaction at LEPS/SPring-8. Significant peak structures were not found in
MMd(K+p-) spectrum, and the upper limits of the production cross section were determined.
Main component of background processes were found to be quasi-free processes (g p→ L(1520) K+, g N→ L/S p K+p-).
LEPS2 has potential for more sensitive search experiments. 2013/11/1 21Hadron in nucleus @ Kyoto University
Collaborators
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Thank you for your attention!
Hadron in nucleus @ Kyoto University