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

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

+: 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 July/29/05 SPring8/LEPS WS

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

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

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

Asymptotic wave function () 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 July/29/05 SPring8/LEPS WS

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

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 July/29/05 SPring8/LEPS WS

X (Why missed) Lowest order decay mode X ! 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. July/29/05 SPring8/LEPS WS

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

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

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

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

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

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

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

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

Typical cross section p0 production cross section ~ 5 mb ~10-3 of p0 K+ 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

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

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.

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

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

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+- July/29/05 SPring8/LEPS WS

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

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

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

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

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

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

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