Isospin breaking a0-f0 mixing

Präsentation zum Thema: "Isospin breaking a0-f0 mixing"—  Präsentation transkript:

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

2 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

3 Observables? KK a0 I3= –1 +1 f0 ph pp
m = (984.7±1.2) MeV/c (“average“) G = ( ) MeV/c (“estimate“) m = (980±10) MeV/c (“estimate“) G = ( ) MeV/c (“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

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

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

6 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

7 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, (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

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, (2003) Dominant channel dd  4He f0(I=0)  4He a00(I=1)  4He p0h ?? (12.7 ± 2.2) pb  Similar to dd  4He p0  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) ~ ( ) pb Pilot measurement: dd  4He a00/f0  4He K+ K– ANKE Markus Büscher

9 Details in: C.Hanhart, nucl-th/0306073
dd   (p0h) vs. dd   p0 Details in: C.Hanhart, nucl-th/ 20 m Production n Propagatio CSB /f a N ÷ ø ö ç è æ G 1 - 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

10 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

11 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, (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

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 Markus Büscher

13 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

14 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, (2003) nucl-ex/ Markus Büscher

15 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