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

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

Observables? KK a0 I3= –1 +1 f0 ph pp 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 a0– a00 f0 a0+ G(KK/ph) = (0.183±0.024) (“seen“/“dominant“) I3= –1 +1 f0 ph pp 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

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

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

First „simple“ experiment The a0/f0(980) at COSY Reaction Where? Result Goal pp  pp K+K- COSY-11 ANKE a00/f0 contribution?? pp  d K+K0 a0+ channel dominates  d p+h WASA First „simple“ experiment for WASA (2006) pn  d K+K- (Feb. 2004)  d p0h Angular asymmetries a0-f0 mixing pd  3He K+K- MOMO  3H K+K0 dd  4He K+K- Winter ’04/05?  4He p0h Isospin violation Markus Büscher m.buescher@fz-juelich.de

p(2.65 GeV)pdK+K0 at ANKE K+ d [(KK)S d]P + [(KK)P d]S V.Kleber et al., PRL 91, 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)S d]P + [(KK)P d]S tot(pp  dK+K0) = (38 ± 2stat ± 14sys) nb  Dominance of a0+ channel Markus Büscher m.buescher@fz-juelich.de

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

Details in: C.Hanhart, nucl-th/0306073 dd   (p0h) vs. dd   p0 Details in: C.Hanhart, nucl-th/0306073 20 m Production n Propagatio CSB /f a N » ÷ ø ö ç è æ G 1 µ - t << d p0 h a0 f0 propagation of a0/f0 CSB in production or p0/h p0 a p0 a h 1. Abschätzung des Faktors 20: Betrachtet werden nur die UNTERSCHIEDE der zwei Graphen dd -> alpha a0. Beim linken ist zusätzlich noch der eta-Propagator zu berücksichtigen. Dieser ist gleich 1/(t - m(eta)^2) ~ 1/t = 1/(m_N m_a0/f0). Beim rechten Prozess gibt es zusätzlich die direkte a0-f0 Mischung, welche proportional zu 1/(m Gamma) ist (d.h. „Überlappfaktor“ a0-f0). Die direkte a0-f0 Mischung ist daher KINEMATISCH gegenüber der pi0-eta Mischung verstärkt.  ? d d d d Markus Büscher m.buescher@fz-juelich.de

More a0-f0 mixing ... L =  K+ K0 d p0 h f0 a0 a f0 a0 f0 a0 K– K0 _ Further enhancement: “Kaon loops“ K+ K0 d p0 h f0 a0 a f0 a0 f0 a0 L =  K– K0 _ 8 MeV CSB amplitude “normal“ CSB o(1%) 1. Abschätzung des Faktors 20: Betrachtet werden nur die UNTERSCHIEDE der zwei Graphen dd -> alpha a0. Beim linken ist zusätzlich noch der eta-Propagator zu berücksichtigen. Dieser ist gleich 1/(t - m(eta)^2) ~ 1/t = 1/(m_N m_a0/f0). Beim rechten Prozess gibt es zusätzlich die direkte a0-f0 Mischung, welche proportional zu 1/(m Gamma) ist (d.h. „Überlappfaktor“ a0-f0). Die direkte a0-f0 Mischung ist daher KINEMATISCH gegenüber der pi0-eta Mischung verstärkt. N.N.Achasov et al., PLB 88, 367 (1979) Markus Büscher m.buescher@fz-juelich.de

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

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

I.d. of ppdK+K0 events @ ANKE Spectrometer dipole COSY beam 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 p d K+ t Background < 10% Markus Büscher m.buescher@fz-juelich.de

First Results on the a0+ [(KK)P d]S + [(KK)S d]P p p  d K+K0 (ANKE) Fit: [(KK)P d]S + [(KK)S d]P tot(pp  dK+K0) = (38 ± 2stat ± 14sys) nb (pp  da0+  dK+K0) = 83% · tot Q = 46 MeV V.Kleber et al., PRL 91, 172304 (2003) nucl-ex/0304020 Markus Büscher m.buescher@fz-juelich.de

p(2.65 GeV)ndK+K- at ANKE K- K+ d m(K+)+m(K-) inv. mass (K+K-) very preliminary!! 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