Update on a 0 (980) P.Gauzzi

2 Main problem From event counting: Br(  0  ) = (6.70  0.26)  with  Br(  0  ) = (7.22  0.52)  with  +    0 Compatible at 2  level (excluding the common uncertainty) Combined fit to the spectra: Br(  )/Br(       )= 1.58  0.04 (free parameter) Br(  )/Br(       )=1.73  0.03 from PDG Marginally compatible ( 8-9% discrepancy  3  ) Checks on efficiencies  OK Checks on background subtraction procedure  OK  Check the normalization: 1) check integrated luminosity 2) Bhabha lumin. vs  3  0

3 Check on bad runs N 5  /L N final /L Criterion: reject runs 5  far from the average (N 5  /L = 1.7) : from to pb : from to pb -1

4 Final sample datadata ω  0  7 f 0   DATA  7  % % % ω0ω % % %  0  0  (f 0  ) % % %  3  920.8%1100.6% %  5  380.3%600.3%980.3 % Tot. Bckg % % %  0  events (-101 evts.)

5 Final sample

6 Branching ratio N -  i B i = 4994 ; 8271  = 38.5 % ; 38.8 % L = pb -1 ; pb -1   = 3090 nb from  (  ) = (40.2  1.0) nb (M.Dreucci – Capri ’03) Br(  ) = (39.38  0.26) % Br = 6.61  ; 6.93  (  5% difference) [ Weighted average: (6.80  0.09  0.24)  ]

7 Normalization to  3  0 events N  7 = 1.5  10 6 ; 2.6  10 6 (contam. = 1.5 % ; 1.2 % )   7 (MC) 73.1 % ; 81.2 % Br(  ) = 1.3% Br(  3  0 ) = % Br = 6.90  ; 6.98  (  1% difference) Weighted average : (6.95  0.09  0.22)   s (MeV)

8 Kaon loop fit Neutral 22 Br(  0  ) = 7.0  Br(  a 0  ) = 6.8  (only scalar part)

9 Kaon loop fit Combined fit (Br(  )/Br(       )=1.73  0.03 from PDG) now discrepancy  2-3% (instead of 8-9%) (  ) (  π + π  π 0 ) Including last point of the charged spectrum  2  181, P(  2 )  0.6% 22 22

10 No structure fit If mass free  non reasonable values: M < 900 MeV 22 Br(  0  ) = 7.1  Br(  a 0  ) = 6.6  (only scalar part)

11 No structure fit (  ) (  π + π  π 0 ) 22 22

12 Conclusions on normalization Two effects: 1)Bad runs:  10 pb -1   2.5% increase in Br (neutral) 2)Spread in  s (especially for 2001)   2.5% increase in Br  Br from 6.7  to  7.0  difference with respect to the charged channel   3% (compatible with the uncertainties on Br(  ) and Br(       ))

13 SU(3) couplings KL and NS models do not make predictions on the structure Relations among couplings can be derived from SU(3) These relations are different for the qqbar and 4q cases For example, for the a 0 (980): KL NS (L  M) g a0  /g a0KK

14 f 0 /  couplings Complicated by mixing Achasov:  S = 0 or 90° for qqbar;  S = 90° for 4q (no mixing) Bugg: 17.3° or -29° “ ;  15.7° “ (g f0  /g f0KK from BES, J/  +  ,  K + K  ) Escribano: -8° C.Gatti: -13°

15 Claudio’s suggestion:  S can be derived from the ratio g  f0  /g  a0  It could work for 4q, but... In the qqbar case  does not couple to a 0  OZI violating contributions have to be taken into account ? SU(3) couplings for f 0 and  s s q q  a0a0 g  f0  /g  a0  KL NS

16 SU(3) couplings for f 0 and  Exercise: get  S from  couplings, fixed in KL fit to Dalitz plot, taken from Achasov-Kiselev paper  g  ππ = 2.4 GeV; g  KK = 0.55 GeV

17 f 0 couplings KL π 0 π 0 NS π 0 π 0 KL π + π ─ NS π + π ─ (Escribano L  M) g f0π  /g f0KK (BES data: J/  π + π ─,  K + K ─  0.49)

18 f 0 /a 0 ratio g f0KK /g a0KK Kaon loop No Structure (f 0  0  0 ) (f 0  +   ) (f 0  0  0 ) (f 0  +   )

19 g SKK KL NS g a0KK (Escribano L  M) Not SU(3) predictions KL π 0 π 0 NS π 0 π 0 KL π + π ─ NS π + π ─

20 Br(  0  ) CMD-2 SND KLOE ’00 KLOE ’01-02 Event counting Kaon Loop No Structure KLOE ’00 (Not SU(3) predictions)

21 gSgSgSgS The coupling g  S  can be related to the strange quark contents of the mesons Meson g  M  (GeV -1 ) 00  0.13  0.71 ´´  0.75 a 0 (980)1.5 – 1.8 f 0 (980)1.2 – 4.1 Increasing s-quark content  2

22 Conclusions on couplings Data do not seem incompatible with an SU(3) picture This can be used to discriminate between qqbar and 4q (at the moment qqbar model seems slightly preferred, but no conclusions can be drawn) A trial to fit all f 0 and a 0 spectra together within SU(3) can be done: all the couplings can be written in terms of few parameters: g SPP,  S, g VS , and  P (already measured in  /  decays) However the KL fit on a 0 (neutral spectrum only), by fixing the ratio g a0  π /g a0KK, does not converge