1. Study of Kaon-pion interaction
T. Kishimoto
Osaka University
July/29/05
SPring8/LEPS WS

2. Contents + as a KN bound state X as a K bound state
Experiment to search for X (KEK-PS E548)
Scalar meson and meson-meson interaction
Experiment to study strange scalar meson
July/29/05
SPring8/LEPS WS

3. +: Another explanation
Consistent theoretical (quark) model
yet to be worked out
KN bound state
arXiv:hep-ex/ (T.K and T.Sato and others)
Mass ~1540 MeV
M(KN) ~1570 MeV (30 MeV bound)
10 MeV/particle (usual)
Spin parity ½+ (original prediction)
K  N system (s-wave) ½+
This conjecture explains all Q+ properties particularly
Narrow width
Seen in Low Q, unseen in High Q
July/29/05
SPring8/LEPS WS

4. Could + be a KN bound state
Known two Body interaction
N: weakly attractive
KN: weakly repulsive
K weakly attractive
K int. may have ambiguity
So strong to make K bound state
No bound state
X (new scaler particle)
July/29/05
SPring8/LEPS WS

5. Width of + in KN conjecture
In order  to decay
KN ! KN ( has to be absorbed in N)
N (s-wave) ! N (p-wave)
K-N (s-wave) ! K-N (p-wave)
KN have to interact simultaneously
Width ~ (strong) (R(int)/R())6
R(int): Radius of Interaction
R(): Radius of 
July/29/05
SPring8/LEPS WS

6. How to Decay (R(int)/R())6 p p K K K N N N p p s s R(int) R() Decay
July/29/05
SPring8/LEPS WS

7. Asymptotic wave function ()
Radius of + (and X)
Asymptotic wave function ()
EB=30 MeV MeV
r~ 2 fm r~ 3 fm
Extended object
Seen only in
Low momentum transfer reaction
July/29/05
SPring8/LEPS WS

8. Width of + in KN conjecture
Width ~ (strong) (R(int)/R())6
(strong) ~ a few 100 MeV
R(int) ~ 1 fm Radius of Interaction
R() ~ 3 fm Radius of 
() ~ 300 x (1/3)6 ~ 0.3 MeV
Consistent with observation
Production of Q+ → low q2 reaction
July/29/05
SPring8/LEPS WS

9. New hypothetical particle X: K bound state
K interaction may be strong enough to make a bound state: New particle X
→ 0+ scalar particle
Binding energy less than 30 MeV
If deeper than 30 MeV Q+ decays into N and X
Probably a few MeV bound
Very extended object
July/29/05
SPring8/LEPS WS

10. X (Why missed) Lowest order decay mode X ! K
No strong decay MX< MK + Mp
No X→K  decay
(0+ → L non cons. )
No X→K e+e-
(vec. curr. vs axial charge (0+→ 0-)
No such decay mode is listed in PDG
No experimental searches ever made (Probably)
If it exists.
Hard to believe but possibility is there.
July/29/05
SPring8/LEPS WS

11. Experiment to search for X
extended object→Low q2 reaction
r(X)~4fm: q2~ 50 MeV/c
Lowest q2 reaction
p(K-+ , X-+)p
@PK~1 GeV/c
q ~ 50 MeV/c
X ! K
July/29/05
SPring8/LEPS WS

12. How to measure (KEK-PS-E548)
p(K-+ , X-+)p, X! K  
Measure Kaon momentum in coincidence with  rays
BG process: p(K-+ , K -+ 0), 0 !  
X particle gives highest PK
Measure invariant mass of K and two ‘s
Dedicated detector system
Study of K final state interaction
July/29/05
SPring8/LEPS WS

13. Cross section PK~1.05 GeV/c Inelastic : ~5 mb ( production)
(X) ~ (K) x f
f: low relative momentum
phase space
Reaction mechanism
b/sr order (1/1000)
KEK-PS E548
July/29/05
SPring8/LEPS WS

14. K + momentum (PK=1 GeV/c)
K + scattering angle (cos q)
K + momentum (MeV/c)
K + p → X + p
K + p → K + p 0 p
Max
950 MeV/c
Signal
Background
Max
830 MeV/c
July/29/05
SPring8/LEPS WS

15. Experimental condition (E548)
K+ beam from K2 beam line at KEK-PS
PK=1.2 GeV/c
50k for 3x1012ppp
Target: 20cm thick H2O and 20 cm thick CH2
Trigger
(K+, K+) x NaI(>5 MeV)
Rate ~ 500 ev/spill
NaI
Target region: 5x5 top and bottom
10.5 cm from the beam center
Forward counter: 3x4 top and bottom
13cm from the beam center
Data taking went well (2 days in this April)
July/29/05
SPring8/LEPS WS

16. Spectrometer E548 Study of kaonic nuclei by (K-, p) reaction
Search for X particle by (K+, K+ gg) reaction
July/29/05
SPring8/LEPS WS

17. Current setup of E548 NaI 5x5 KURAMA NaI 3x4 FAC γ VZH BAC 1 BAC 2 LC
20cm
BAC 1
BAC 2 LC BS K+
Target(water)
BQC
K+Beam 1.2GeV/c
10.5cm γ CV
July/29/05
SPring8/LEPS WS

18. K+ momentum Tagged by 2γ PK=1.2 GeV/c X particle production
2 γ backward
K+ momentum
π0 production
July/29/05
SPring8/LEPS WS

19. Typical cross section p0 production cross section ~ 5 mb ~10-3 of p0K+ X+
p0 production cross section ~ 5 mb
~10-3 of p0
1 MeV bound X (r~ 10 fm)
~10-2 of p0
5 MeV bound X (r~ 4 fm) p0 p p
July/29/05
SPring8/LEPS WS

20. X particle implies K bound system X explains + properties
X might have been missed experimentally
If found, it means we found a new scalar particle (like k, strange partner of σ)
It is not only a solution of + but opens new world.
If not found, we still want to look for K final state interaction
July/29/05
SPring8/LEPS WS

21. Study of meson-meson interaction at SPring8/LEPS
Recent observation of s meson.
How to produce scalar mesons
Beijin exp. to produce s by J/Y factory
Selection of spin parity
This may be true for other searches
July/29/05
SPring8/LEPS WS
Dirac exp.

22. J/Ψ(1-)ω(1-)π+π-(0+) π+ π- π0 (a)|M π+ π- π0 –Mω|<40MeV/c2
ω (1－)
(b) π+ π- against ω
f2(1270) (2+)peak
(c) ωπ invariant mass
b1(1235) (1+)peak
(d) Dalitz plot
July/29/05
SPring8/LEPS WS

23. Method II : several parameterization of the sigma pole are used
0++
2++
b1(1235)
background
July/29/05
SPring8/LEPS WS

24. Study of K p interaction at SPring8/LEPS
X particle (X+), X0, X0, X－
X+: mK+ +mp0=628.62MeV, mK0 +mp+=637.24MeV
X0: mK+ +mp-= mK- +mp+= MeV
Isospin state or charge state
Threshold region X ?
4.59
4.03
K+-+p0
K-++p+-
K0+p+-
July/29/05
SPring8/LEPS WS

25. Spin parity relation K* 1－ 1/2+ 3/2－ 0+ 1－ 1/2+ 1/2+ 1－ July/29/05
SPring8/LEPS WS

26. Study of strange scalar meson at SPring8/LEPS
X or k production
Photon energy
July/29/05
SPring8/LEPS WS

27. Kp parameters
Nucl.Phys.B133:490,1978
July/29/05
SPring8/LEPS WS

28. Missing mass spectrum k k K* L(1116) gated L(1520) gated
attractive but no X k X
L(1520) gated
with X (looks repulsive)
July/29/05
SPring8/LEPS WS

29. Resolution Missing mass Eg dependence
2GeV beam, mX~0.63 GeV
L(1520): mp~0.94, EL~2.07, pL~1.4
DmX~0.4Eg
L(1116): mp~0.94, EL~1.69, pL~1.27
DmX~0.8Eg
July/29/05
SPring8/LEPS WS

30. Resolution EL dependence L(1520): mp~0.94, EL~2.07, pL~1.4 DmX~ -2.5ELK－
L(1520) X Kp
July/29/05
SPring8/LEPS WS

31. Experiment Hydrogen target Charged particle detector Gamma detector
Already available at LEPS,
though configuration is not straightforward
July/29/05
SPring8/LEPS WS