1. Scalar mesons and d0-d2 at KLOE
Claudio Gatti, Università di Roma La Sapienza - INFN
For the KLOE collaboration
DANE and KLOE
Scalar mesons a0 and f0
Measurement of BR(00,0)
Measurement of BR(KS+-/00) and 0-2
Conclusion
Conversano June

2. DAFNE
electron-positron collider

3. KLOE DC EmC Stereo geometry: 60-150 mrad Cell size: 2x2 3x3 cm2
Spatial resolution:
EmC
Lead scintillating-fiber calorimeter
Thickness: 15 radiation lengths (x01.5cm)
Granularity: 4.4x4.4 cm2
Trigger: based on DC and EmC signals.

4. Scalar mesons a0(980) I=1 f0(980) I=0 BR((f0 a0) )  10-5 qq model
ma = mf ~ 980 MeV  SS disfavoured S q
OZI rule
Suppression of  decays into final states without strange quarks
BR((f0 a0) )  10-5

5. Scalar mesons   qqqq model KK molecule K+ K- a0, f0 Diffuse system
R2 fm, F2(R)<1
Compact system
R<1 fm, F2(R)1
BR ~ 210-4F2(R)
BR2 10-4
BR < 10-5
if Fa0=Ff0 and gakk=gfkk

6.  f0(980),a0(980) f000 a00 5 +- 5  gKK gSKK
gSPP p  S 
PP invariant mass spectrum fitted by folding the shape predicted by a model with experimental resolutions:
Fitting function:
Parameters: gSKK gSPP MS

7.  00 BR(00)= (1.090.03stat0.05syst)10-4 Signal  00
BKG
e+e- 00
Selection:
5 prompt clusters.
ETOT>800 MeV, PTOT< 200 MeV/c.
Kinematic fit for E, P conservation and photon pairing.
cut on pion mass |M-M|< 5.
BKG rejection (M, cos, 2).
L~16 pb-1
~5 107 
243861 events
PL B537 (2002)
BR(00)= (1.090.03stat0.05syst)10-4

8.  05,+-5 BR(0)= (8.50.5stat0.6syst)10-5
Signal  5
BKG
e+e-0 00
  00
60736
Signal  +-5
BKG
e+e-0 +- 4
KSKL
19714 0 
BR(0)= (8.50.5stat0.6syst)10-5
PL B536 (2002)
BR(0)= (8.00.6stat0.5syst)10-5

9. Mass spectrum fit BR(f0)= (4.470.21)10-4
BR(a0)= (7.40.7)10-5
R=BR(f0)/ BR(a0)=6.1±0.6
g2(f0KK)/g2(a0KK)= 7.00.7

10. BR(KS+-())/ BR(KS00) and 0-2
In the limit of exact isospin
symmetry, isospin phases and amplitudes can be extracted from
K decays.
0-2=(56.7± 3.8 ) from BR in PDG
8 (Cirigliano
et al. (2000))
Expected 0-2=(47.7±1.5)
from G. Colangelo et al. (2001)
ECUTOFF(MeV)
0-2-em
In the presence of isospin
breaking effect, like EM:
0-2  0-2-em
em  3.2 (Cirigliano et al. (2000))
Data must be analyzed with the inclusion of radiative corrections.

11. BR(KS+-())/ BR(KS00): The tag
KL crash
KS+-
KL crash (30%):
Cluster on barrel
Eclu>100 MeV
0.17 < * < 0.28 ( KL velocity from cluster position and time)
Tag bias

12. KS00   90% KS+-   60% At least 3 neutral clusters.
N. clusters %
<2 2 3 4
>4
1.3
8.6
33.2
56.6
0.3
At least 3 neutral clusters.
Almost inclusive, low sensitivity to accidental clusters and inefficiencies.
  90%
KS+-
Low BKG
2 TRKs from IP extrapolated to the EmC:
120 MeV < pTRK < 300 MeV
  60%

13. KS+-() MC  MC  Efficiency corrected for the
presence of the radiated
photon. The total correction is 0.3%.
ppg
New MC implemented without
any cutoff on the photon energy.
N(Eg >50 MeV)/NTOT = 2.6x10-3

14. BR(KS+-())/ BR(KS00)
Y2000: ~17 pb-1
PL B538 (2002)
0 - 2 - em=(47.8±2.8)
Comparing with G.Colangelo et al. em=(-0.1±3.2)
still in agreement with Cirigliano et al.

15. Conclusion Perspectives
With ~17 pb-1 of data collected during the year 2000 KLOE measured:
The BRs for 00 0 identifying 2440 and 800 events respectively. The mass spectra have been measured and unfolded. The estimate of the f0 and a0 coupling constants was obtained by performing a (model dependent) fit to these spectra.
The ratio of BRs KS+-/00 correcting for the efficiency of the radiated photon. This measurement allows an accurate determination of 0-2-em which now is in agreement with the expected value.
Perspectives
Higher statistics collected during the years 2001 and 2002 allows: 2-dimensional mass spectra studies (Dalitz plots)
The study of +- decays
Reduction of systematics for BRs KS+-/00 to 0.1%.

16. Isospin mixing
Isospin mixing 
(  45)
=(472)
7.00.7
6.10.6

17. Fit results
M(f0)= 973  1 MeV
g2(f0KK)/4 = 2.790.12 GeV2
g(f0KK)/g(f0)=4.00 0.14
g() = 0.0600.008
M(a0)= MeV (FIXED)
g2(a0KK)/4 = 0.400.04 GeV2
g(a0)/g(a0KK)=1.35 0.09

18. 2001-2002 data ’00 data ’01+’02 data KLOE preliminary: ’01 + ’02 data

19.  +-
Preliminary
data ~ events f0  