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Study of Kaon-pion interaction

Study of Kaon-pion interaction. T. Kishimoto Osaka University. 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.  + : Another explanation.

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Study of Kaon-pion interaction

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  1. Study of Kaon-pion interaction T. Kishimoto Osaka University

  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

  3. +: Another explanation • Consistent theoretical (quark) model • yet to be worked out • KN bound state • arXiv:hep-ex/0312003 (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

  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)

  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 

  6. How to Decay N p p K p N p s s K R(int) R() Decay (R(int)/R())6 N K p

  7. Radius of + (and X) Asymptotic wave function () EB=30 MeV 15 MeV r~ 2 fm r~ 3 fm Extended object Seen only in Low momentum transfer reaction

  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

  9. New hypothetical particle X: K bound state • K interaction may be strong enough to make a bound state: New particle X • 0- + 0- → 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

  10. X (Why missed) • Lowest order decay modeX ! K • No strong decay MX< MK + Mp • No X→K  decay • (0+ → 0- + 1- 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.

  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

  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

  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

  14. K+ momentum (MeV/c) K+p → X+p K+ scattering angle (cos q) K+ momentum (MeV/c) K+p → K+p0p K+ scattering angle (cos q) K+ momentum (PK=1 GeV/c) Max 950 MeV/c Signal Background Max 830 MeV/c

  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)

  16. Spectrometer E548 Study of kaonic nuclei by (K-, p) reaction Search for X particle by (K+, K+ gg) reaction

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

  18. K+ momentum Tagged by 2γ PK=1.2 GeV/c K+ momentum X particle production 2 γ backward K+ momentum π0 production

  19. Typical cross section • 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) K+ X+ p0 p p

  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

  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 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

  23. Method II : several parameterization of the sigma pole are used 0++ 2++ b1(1235) background

  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+= 633.21MeV • Isospin state or charge state • Threshold region ? X 4.59 4.03 K+-+p0 K-++p+- K0+p+-

  25. Spin parity relation 1－ 1/2+ 3/2－ 0+ K* 1－ 1/2+ 1/2+ 1－

  26. Study of strange scalar meson at SPring8/LEPS • X or k production • Photon energy

  27. Kp parameters Nucl.Phys.B133:490,1978

  28. Missing mass spectrum K* L(1116) gated k L(1520) gated attractive but no X k X L(1520) gated with X (looks repulsive)

  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

  30. Resolution • EL dependence L(1520): mp~0.94, EL~2.07, pL~1.4 DmX~ -2.5EL L(1116): mp~0.94, EL~1.69, pL~1.27 DmX~ -2.1EL p K－ L(1520) X Kp

  31. Experiment • Hydrogen target • Charged particle detector • Gamma detector Already available at LEPS, though configuration is not straightforward

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