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Atsushi Tokiyasu(for LEPS collaboration)
Experimental Nuclear and Hadronic Physics Laboratry,
Department of Physics, Kyoto University
Search for Kaonic nuclei at SPring8/LEPS
GCOE Symposium12th – 14th .Feb.2013 @ Kyoto University
GCOE Symposium @ Kyoto University
strangeness in nuclei
2013/2/13 2 / 11
ds us,
SU(3) octet baryon SU(3) nonet meson
L K?
Hyper nucleiShrinkage impurity effect.
nuclear force in SU(3)
Kaonic nuclei
new form of the nuclei
whether exist or not?
What happens in nuclei?
uds
hyperon kaon
GCOE Symposium @ Kyoto University
dependent on the models of KN interaction the calculation methods.
Formation of Cold (T=0) and Dense (r > 2r0) nuclei.
2013/2/13 3 / 11
K can be bound in the nuclei by strong interaction.
K N interaction (I=0) is strongly attractive !X-ray shift of Kaonic Hydrogen
K- p scattering data
2-body: KN : L(1405) ?
3-body: KNN : lightest nucleus.
K-pp the strongest bound state in 3-body systems
Theoretical prediction (All theory support the existence)B.E. = 20-100 MeV
G = 40- 110 MeV
If G > B.E, it is difficult to observe experimentally.
Ref: Particle Data Group
Kaonic nuclei
GCOE Symposium @ Kyoto University
Experiments
2013/2/13 4 / 11
)()( syststat 34
65115
)()( syststat 23
141167
)()( syststat 53103
)()( syststat 108118
FINUDA @ DAFNE (2005) DISTO@ SATURNE(2010)stropped K- on (6Li, 7Li, 12C, 27Al and 51V) p p L p K+
B.E. =B.E. =
G =G =
invariant mass (L + p) Missing mass (K+)
MeV
MeV
MeV
MeV
M.Agnello, Nagae and Fujoka et al., PRL 94, 212303 (2005) T.Yamazaki et al., PRL 104, 132502 (2010)
K-pp L p , S0 p, S+ n (non-mesonic decay) easy to identify experimentally S p p (mesonic decay)
GCOE Symposium @ Kyoto University
Summary of the introduction
K-pp is the lightest kaonic nuclei.
Existence of K-pp is not established.
Experimental search using different reactions are awaited!
Forthcoming experiments3He(K-, n)X E15 @ J-PARC
D(p+, K+)X E27 @ J-PARC
g D K+ p- X LEPS @ SPring-82013/2/13 5 / 11
Prof.Nagae’s talk
GCOE Symposium @ Kyoto University
g D K+ p - X reaction
2013/2/13 6 / 11
K+
p-
g
“K” exchanged in t-chanel unique for g-induced reaction g ( J = 1)polarization observables are available.
K-pp is “soft” object. small momentum transfer detect K+ and p- at forward angle
Search for a bump structure in the missing mass spectrum Mx
2 = (Eg + MD – EK- Ep)2 - (pg – pK - pp)2
independent of decay chanel.
K, K*Y*
p
npK-
p
Y*
(Eg, pg) (EK, pK)
(Ep, pp)
(MD,0) Y* door-way.
GCOE Symposium @ Kyoto University
SPring-8 “Super Photon ring-8 GeV”
2013/2/13 7 / 11
Data take:2002/2003, 2006/2007 7.6 x 1012 photons on LD2 target
SPring-8: 8 GeV electron storage-ringLEPS : hadron physics using g beam
Back-word Compton Scattering
e
e
Detect withTagging counter
Eg=1.5 - 2.4 GeVexperimentalhatch
355nm laser8 GeV
LEPS
DEg=12 MeV
GCOE Symposium @ Kyoto University
LEPS spectrometer
2013/2/13 8 / 11
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(1.5-2.4 GeV)
p-
K+
GCOE Symposium @ Kyoto University
particle identification
2013/2/13 9 / 11
K+
p- Dp/p ~ 6 MeV/c @ 1 GeV/c
TOF (Time of flight)
m2 = p2(1/β2 - 1)
line tracking + Runge-Kutta method.
mass p = 938.3 MeVmass K+ = 493.7 MeVmass p- = 139.6 MeV
c.f.
p
p+
K-
0
GCOE Symposium @ Kyoto University
Missing Mass Spectrum
2013/2/13 10 / 11
Error Bar : statistical uncertainty (~5%)Red Box : systematic uncertainty (~20%)Hatched : discrepancy between datasets (~12%)
preliminary
No bump structure was observed!upper limit of cross section
L S
n
search region: Mass = 2.22 - 2.36 GeV/c2
B.E. = 150 - 10 MeV
acceptance was corrected with Monte-Carlo simulation
expected signal
GCOE Symposium @ Kyoto University
Upper Limits of differential cross section
2013/2/13 11 / 11
preliminary
-G= 20 MeV 0.05 - 0.25 mb
- G = 60 MeV 0.15 - 0.6 mb
- G =100 MeV 0.15 - 0.7 mb
a few % of typical hadron production cross section.
g N L K (~8 pmb )g N S K (~4 p mb)
B.E. 15 points (10-150 MeV)G 3 points
upper limits of cross section were determined log likelihood ratio method
GCOE Symposium @ Kyoto University
Conclusion and future prospect
The existence of Kaonic nuclei is not established.
K-pp was searched for using g D K+ p - X reaction
No bump structures were found, and the upper limits of differential cross section were determined to be a few % of typical hadron production cross section.
Future prospectdetect the decay products from K-pp. increase S/N
search for other charge states using gDK+ K-pn , gDK+p+ K-nn
2013/2/13 12 / 11
GCOE Symposium @ Kyoto University
Collaborators
2013/2/13 13 / 15
GCOE Symposium @ Kyoto University
Appendix
2013/2/13 14 / 15
GCOE Symposium @ Kyoto University
Appendix
Meritdeuteron small nuclear effect(FSI).
additional p- emission reduce the momentum transfer.
K can be exchanged.
polarization observable is available.
Demeritsmall cross section (~nbarn).
many background source
limited information on hadron resonance.
necessary to detect the decay product.
2013/2/13 15 / 15
GCOE Symposium @ Kyoto University
Calculation of Upper Limits
2013/2/13 16 / 15
preliminary
preliminary
Upper Limit was calculated with log Likelihood ratio method
Background proces - g p K+ p- L - g p K+ p- S - g p K+ p- S(1385) - g p K+ p- S(1385)- - g p K+ p- p Lconstant offset
Signal Breit Wigner distribution
-2DlnL = 3.841 upper limit (95% C.L.)
Signal Yield
GCOE Symposium @ Kyoto University
Theoretical calculation
2013/2/13 17 / 15
Binding Energy DecayWidth
Method
Yamazaki and Akaishi 48 MeV 61 MeV PhenomenologicalVariatioal Method
Dote, Hyodo and Weise 20±3 MeV 40-70 MeV Chiral SU(3)Variational Method
Ikeda and Sato 60 – 95 MeV 45 - 80 MeV Chiral SU(3)Fadeev Calculation
Shevchenko, Gal and Mares
50 – 70 MeV 90 – 110 MeV PhenomenologicalFadeev Calculation
S. Wycech and A. M. Green
56.5~78 MeV 39~60 MeV
Uchino, Hyodo and Oka
depend on L* NVariational Method
All calculations predict that K-pp can exist!!
However… B.E. = 20 – 100 MeV G = 40 – 110 MeV Depending on the K N interaction model and Calculation Method.
GCOE Symposium @ Kyoto University
Background processes
2013/2/13 18 / 15
preliminary
15 quasi- free processes were considered for fitting.gN Y K+ Y K+ p- Y* K+ p- Y K+ p- p
The main background (~20 %)gn K+ L(1520) Sp Lpp
g N K+ p- XMM(K+)
MM(K+,p-)
MM(K+)
MM(K+,p-)
c2/ndf ~ 1.3
Yhyperon ( ,L S)Y* hyperon resonance ( (1405), (1385)L S …)