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Isospin breaking a 0 -f 0 mixing

Isospin breaking a 0 -f 0 mixing. ... a tool to investigate (not only!) the structure of the light scalar mesons. Markus Büscher Forschungszentrum Jülich Germany. Nonet of light scalar mesons J P =0 +. Possible candidates. S. f 0 (500) (“ “) k(800) f 0 (980) a 0 (980) f 0 (1370)

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Isospin breaking a 0 -f 0 mixing

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  1. Isospin breaking a0-f0 mixing ... a tool to investigate (not only!) the structure of the light scalar mesons Markus Büscher Forschungszentrum Jülich Germany Markus Büscher m.buescher@fz-juelich.de

  2. Nonet of light scalar mesons JP=0+ Possible candidates S f0(500) (““) k(800) f0(980) a0(980) f0(1370) K0*(1430) a0(1450) f0(1500) f0(1710) K*(?) K*(?) COSY a0-(?) a00(?) f0(?) a0+(?) } I f0(?) 9 states K*(?) K*(?) } 10 states „Genuine“ qq 4-quark states KK molecules Nature of these states?? The light scalar resonances Markus Büscher m.buescher@fz-juelich.de

  3. Observables? KK m = (984.7±1.2) MeV/c2 (“average“) G = (50...100) MeV/c2 (“estimate“) m = (980±10) MeV/c2 (“estimate“) G = (40...100) MeV/c2 (“estimate“) a0 G(KK/ph) = (0.183±0.024) (“seen“/“dominant“) a0– a00 f0 a0+ –1 0 +1 I3= f0 pp ph G(KK/pp) = ... (“seen“/“dominant“) • Observables at COSY (yet unknown): • Mass distributions • Branching ratios to KK and ph/pp • (Differential) production cross sections • Isospin ratios (e.g. pn vs. pp reactions) • a0-f0 mixing • Polarization observables a0 COSY limit Markus Büscher m.buescher@fz-juelich.de

  4. The Accelerator: COSY-Jülich COSY (Cooler Synchroton) at FZ-Jülich: • (polarized) p & d beams • phase-space cooling • electron & stochasting cooling • p = 0.30 – 3.70 GeV/c • pp  pp X (mX  1.1 GeV/c2) • dd  a X (mX  1.03 GeV/c2) • pp  pK+ Y* (mY*  1.5 GeV/c2) • internal & extracted beams Markus Büscher m.buescher@fz-juelich.de

  5. The detectors: ANKE & WASA Ready for experiments in 2006 In operation since 1998 WASA ANKE • currently at CELSIUS (Uppsala) • nearly 4p coverage • charged and neutral particle i.d. • frozen pellet target (L ~ few1032 cm-2s-1) • forward spectrometer (small acceptance) • optimized for K+/K- detection • cluster jet target (L ~ few1031 cm-2s-1) Markus Büscher m.buescher@fz-juelich.de

  6. The a0/f0(980) at COSY Markus Büscher m.buescher@fz-juelich.de

  7. p(2.65 GeV)pdK+K0 at ANKE V.Kleber et al., PRL91, 172304 (2003) Q = 46 MeV m(K+)+m(K0) K+ d • K+d coincidence measurement • Identification of ppdK+X events via TOF, E and particle momenta • Identification of ppdK+K0 events via dK+ missing mass 83% Fit: [(KK)Sd]P+ [(KK)Pd]S tot(pp  dK+K0) = (38 ± 2stat± 14sys) nb  Dominance of a0+ channel Markus Büscher m.buescher@fz-juelich.de

  8. a0-f0 mixing in dd  4He p0h • Direct production of a00 in dd  4He a00 ( p0h) is forbidden if isospin is conserved E.J.Stephenson et al., Phys. Rev. Lett. 91, 142302 (2003) • Dominant channel dd  4He f0(I=0) 4He a00(I=1) 4He p0h ?? (12.7 ± 2.2) pb  Similar to dd  4He p0 experiment @IUCF  Strength of a0-f0 mixing unknown • Probably larger than p0-h mixing • Close & Kirk: mixing intensity = 8±3% (data from WA102) • but critizised by Achasov & Kiselev, Oller (15.1 ± 3.1) pb  dd  4HeX cross section unknown • Our estimate: s(dd  4He a00) ~ (50 ... 200) pb • Pilot measurement: dd  4He a00/f0 4He K+ K– ANKE Markus Büscher m.buescher@fz-juelich.de

  9. p0 h p0 h 1 1 a0 µ » t - m m a a N a /f 0 0 f0 a0 << p0 p0 h 1 µ G m a /f a /f d d 0 0 0 0 d d æ ö Propagatio n m p0 æ ö ç ÷ N CSB ç ÷ 20 » » ç ÷ G Production è ø è ø a /f 0 0 Details in: C.Hanhart, nucl-th/0306073 dd   (p0h) vs. dd   p0 propagation of a0/f0 production CSB in or p0/h p0 a a h  ? d d d d Markus Büscher m.buescher@fz-juelich.de

  10. p0 h a0 f0 a d d More a0-f0 mixing ... Further enhancement: “Kaon loops“ K0 K+ a0 a0 f0 f0 L =  K0 _ K– 8 MeV CSB amplitude “normal“ CSB o(1%) N.N.Achasov et al., PLB 88, 367 (1979) Markus Büscher m.buescher@fz-juelich.de

  11. angular distribution of the a0 ph mass distribution pn  pn(d) p0h Kaon loops „direct“a0-f0 or p-h mixing no mixing V.Grishina et al., PLB 521, 217 (2001) V.Kudryavtsev et al., PRC 66, 015207 (2002) a0/f0 mixing in pninteractions  Look, e.g., for angular asymmetries around 90°in pn  d+Meson reactions a00 a00 Markus Büscher m.buescher@fz-juelich.de

  12. People ... M.Büscher, C.Hanhart, V.Hejny, S.Krewald, A.Sibirtsev, H.Ströher IKP, FZ Jülich U.-G.Meißner HISKP, Universität Bonn / IKP, FZ Jülich V.Kleber IKP, Universität zu Köln P.Fedorets, L.Kondratyuk, A.Kudryavtsev ITEP, Moscow, Russia V.Grishina INR, Moscow, Russia A.Dzuba, V.Koptev, S.Mikirtychiants, M.Nekipelov PNPI, Gatchina, Russia and the ANKE collaboration Experiment Theory http:www.fz-juelich.de/ikp/anke Markus Büscher m.buescher@fz-juelich.de

  13. Background < 10% I.d. of ppdK+K0 events @ ANKE Spectrometer dipole T = 2.65 GeV • K+-d coincidence measurement • Identification of ppdK+X events via TOF, E and particle momenta • Identification of ppdK+K0 events via dK+ missing mass COSY beam p d K+ t Markus Büscher m.buescher@fz-juelich.de

  14. Fit: [(KK)Pd]S+ [(KK)Sd]P (pp  da0+  dK+K0) = 83% · tot tot(pp  dK+K0) = (38 ± 2stat± 14sys) nb First Results on the a0+ p p  d K+K0 (ANKE) Q = 46 MeV V.Kleber et al., PRL91, 172304 (2003) nucl-ex/0304020 Markus Büscher m.buescher@fz-juelich.de

  15. m(K+)+m(K-) very preliminary!! inv. mass (K+K-) p(2.65 GeV)ndK+K- at ANKE K- K+ d • D2 as an effective neutron target • K+ K- d coincidence measurement • unobserved spectator proton • First data on f-meson production on neutrons • Narrow a00/f0 signal at small K+K- masses?? Markus Büscher m.buescher@fz-juelich.de

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