1. Experimental Measurement
of the F meson radiative decays into scalars and pseudoscalars mesons
The KLOE Coll. presented by
Camilla Di Donato I.N.F.N. Naples
International Conference on the Structure and Interactions of the Photon

2. KLOE data collected 1999 run : 2.5 pb-1 machine and detector studies
7.5x107 f
published results
2001 run: 190 pb-1
5.7x108 f
analysis in progress
2002 run: 300 pb-1
9.0x108 f

3. KLOE Drift chamber: dp/p < 0.4% xy150 m ; z2 mm
E.m. calorimeter:
sE/E = 5.4% / (E(GeV))
st = 55 ps/(E(GeV))40 ps
98% of 4
Magnetic field: 0.52 T

4. F radiative decays Analysis of 2000 data:  Ldt = 16 pb-1
F  hg / hg Phys. Lett. B541 (2002), 45
F  p0 p0 g Phys. Lett. B537 (2002), 21
F  h p0 g Phys. Lett. B537 (2002), 209

5. F radiative decays Pseudoscalar mesons (JPC= 0-+)
h (547) (I=0)
h (958) (I=0)
Scalar mesons (JPC= 0++)
f0(980) (I=0)
a0(980) (I=1)

6.  / 
The mass eigenstates ,  are related to SU(3) octet-singlet
8, 1 through the mixing angle P
Recent studies based on PT and phenomenological analyses
suggested a two mixing angle scenario
In the quark flavour basis the two mixing angles are almost equal
 mixing is described by only one parameter (P)

7.  /  Br() can probe the gluonic content of 
P can be extracted from the ratio
(Bramon et al., Eur.Phys.J.C7(1999)) :
Br() can probe the gluonic content of 

8.  /  Decays with +- 3 final state:
;+-0;0 Br  310-3
 ; +- ;  Br  210-5
Background from +-0 and KLKS (with KL decaying near the IP)
Analysis cut:
1 vertex in IR with 2 tracks
3 prompt  (E>10 MeV, |cos|<0.93)
Constrained kinematic fit
topological cuts on the energy of particles
tot () = 37 %
tot () = 23 %

´

9.  /  R = Br()/Br() M (MeV)
Main background is 
Selection: elliptic cut in the plane of the two most energetic photons
Phys. Lett. B 541 (2002), 45
M (MeV)
F =0.95 (interference with e+e-( )
N() = 120 12 5 events; N() =  220 events
R = Br()/Br()

10.  /  Using PDG value for Br():
Pseudoscalar mixing angle:
P = (41.8  1.7) (flavor)
 P = (-12.9 1.7) (octet-singlet)
Gluonic content of :
Consistency check: if Z=0  |Y|=cosP
other constraints on X and Y from:
(1) /(0
(2) /(0
(1)
(2)

11.  / 
M (MeV)
100 pb-1 (2001)

12. p+p-7 preliminary N() = 153 12 2000 2001 2002
Selection:
2000
2001
2002
Ep++Ep- (MeV)
dN/dE
dN/dE
Eg (MeV)
Ks  p0 p0
Kl  p+p-p0
Ks  p+p-g
Kl  p0p0p0
data
preliminary
Ks  p0 p0
Kl  p+p-p0
Ks  p+p-g
Kl  p0p0p0
data
Ep++Ep- (MeV)
N() = 153 12
Br() = (7.05± /-0.46)x10-5

13. f f0 (980) g / a0 (980) g
The scalar mesons f0 (980) a0 (980) are not easily interpreted
as qq states
Jaffe(1977) suggested qqqq states
Weinstein, Isgur (1990) suggested KK molecule
Both BR and scalar mass spectra are sensitive to nature
Br(f0)  
Br(a0)  

14. Models Predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989)
f0 model
g2f0KK/(4)
(GeV2) (=g2a0KK/4) (=g2a0KK/4) (=2g2a0KK/4)
gf0 /gf0KK —
Br(00) ~ ~ ~ 0.2
a0 model
g2a0KK/(4)
(GeV2) (=g2f0KK/4) (=g2f0KK/4)
ga0/ga0KK
Br( a0) ~ ~ 0.2

15. Scalar mesons (JPC= 0++)
f0(980) (I=0) f000+-
a0(980) (I=1) a0
Studied decays (data sample: 16 pb-1 from the 2000 data,~5107)
f0 ; f000  5  final state
a0 ; a0  (39%)  5 
a0 ; a0 +-0 (23%)  2 ch. tracks +5 
first observation 
Previous meas.
at VEPP2M

16. 5 g final states cross sect.(nb)
Signal: 00 (f0 ; (500) ; 00) ~ 0.35
 0  0
0 ( a0 ;  00) ~ 0.1
 
Background: e+e-0 00 ~ 0.5
3 (with accidental ’s) (~17)
 000 (with 2 lost) (~14)
Sample selection:
exactly 5 prompt photons
E > 7 MeV
|cos| < to avoid the quadrupole region
5Ei > 700 MeV to reject KLKS neutrals

17. 00 Constrained kinematic fit to improve resolutions
Photon pairing
|M - M| < 5(M)
Reject events with:
|M - M| < 3(M)
 3102 events
<> = 40%
Estimated backgr. (~20%)
e+e-0 00 24
0 16
 000 12
1+cos2 0  

18. Fit to M spectrum gKK gf0KK gf0 Model :
radiative g
gKK
gf0KK
gf0 0 K+ K-
Model :
1) f0 dominated by kaon loop
(Achasov-Ivanchenko, Nucl.Phys.B315(1989))
2) f0 propagator with finite width corrections
3) (500) B-W with M=478 MeV and =324 MeV
(Fermilab E791-Phys.Rev.Lett.86(2001)770)
4) point-like coupling of (500) to 
(Gokalp,Yilmaz,Phys.Rev.D64(2001))
5)  + interference term parameterizations
from Achasov-Gubin, (Phys.Rev.D63(2001))
Two fits:
Fit A : | (f0) + (00 )|2
Fit B : | (f0) + () + (00 )|2
Free parameters: Mf0, g2f0KK, g2f0/g2f0KK, g and (gg)2

19. Fit results A B 2/ndf 109.5/33 43.2/32 Mf0 (MeV) 9624 973 1
g2f0KK/(4)  0.12
(GeV2)
g2f0KK/g2f0  0.14
g — 0.008
(  contribution negligible )
Br(00) = (1.09  0.03  0.05)  (Fit B)
(SND: (1.220.10 0.06)  10-4 ; CMD-2: (1.080.170.09)  10-4)
 Large f0- destructive interference at M < 700 MeV
Br(f0)= (4.47  0.21)  10-4

20. 0 (with ) Events Constrained kinematic fit
to improve resolutions
Photon pairing: (1) 00 ; (2) 0
 reject 00 events
M  < 760 MeV (reject f0 events)
|M - M| < 3(M)
 916 events <> = 32 %
M (MeV/c2)
Events
cos
Data —MC
Estimated backgr.: (~30%)
e+e-0 00 6
00 16
 000 10
  2
Br(0)=(8.510.510.57) 10-5
SND :(8.8 1.40.9)  10 –5 ;CMD-2: (9.0 2.41.0)  10 –5

21. 0 +-5 (+-0)
No background with the same final state
Backgr.: 2 Tracks + 3/4 photons (e+e-0 ; +-0)
( ; +-0)
2 Tracks + 6 photons
(KSKL+-000)
1 vertex in IR with 2 tracks
5 prompt  (E>10 MeV, |cos|<0.93)
Constrained kinematic fit
M+-< 425 MeV (reject KS  p+p-)
 197 events <>=19%
estimated backgr. 44 events
Br(0)=(7.960.600.47) 10-5

22. Fit to Mh spectrum Same model as for the f0 (kaon loop)
Combined fit, relative normalization fixed
to Br()/Br(+-0)
Free parameters:
g2a0KK, ga0/ga0KK and Br(000)
Ma0=984.8 MeV (PDG) fixed
2/ndf /25
g2a0KK/(4) (GeV2)  0.04
ga0/ga0KK  0.09
Br(000) (0.5  0.5)  10-5 5
+-5
Br(a00)= (7.4  0.7)  10-5

23. Summary of fit results f0 parameters are compatible with model
Comparison with predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989)
KLOE
f0 model
g2f0KK/(4) 
(GeV2) (=g2a0KK/4) (=g2a0KK/4) (=2g2a0KK/4)
gf0 /gf0KK  —
Br(00)  ~ ~ ~ 0.2
a0 model
g2a0KK/(4) 
(GeV2) (=g2f0KK/4) (=g2f0KK/4)
ga0/ga0KK 
Br( a0)  ~ ~ 0.2
f0 parameters are compatible with model
a0 parameters seem not compatible with model

24. f f0(980) g / a0(980) g M (MeV) 2001+2002 data 2000 data
Phys. Lett. B 537 (2002), 21
M0 (MeV)
Phys. Lett. B 536 (2002), 209

25. Conclusions
First KLOE published papers on f radiative decays, 2000 events:
Br() = (6.100.610.43)10-5
P = (41.8  1.7) (flavor)
Br(00) = (1.09  0.03  0.05)  10-4
Br(f0) = (4.47  0.21)  10-4
Br(a0) = (7.4  0.7)  10-5
Analysis in progress on events  500pb-1:
more statistic and models with more free parameters

27. ====================================================== Author : KLOE Collab. (Speaker: Camilla Di Donato) Type :
Experimental Measurement of the Phi meson radiative decays into scalars and pseudoscalars mesons.
The Kloe experiment has measured the radiative decays of the Phi meson into pi0, eta and eta'(958); these measurements are relevant to assess the mixing in the pseudoscalar nonet as well as to evaluate the gluon content in the eta'(958). Moreover also the radiative decays into pi0 pi0 gamma and eta pi0 gamma have been measured. These decays are dominated by the final states f0(980) and a0(980). The measurement of the branching ratios and of the pi0-pi0 or eta-pi0 invariant mass spectrum helps to understand the controversial nature of the above scalar mesons. ==================================================