1. KLOE results on hadron physics
Hadron07, Frascati 09/10/2007
KLOE results on hadron physics
Cesare Bini
Università “La Sapienza” and INFN Roma
on behalf of the KLOE collaboration
Outline:
The KLOE experiment
Results on pseudoscalar mesons
Results on scalar mesons
Prospects

2. 1. The KLOE experiment at DANE
Frascati Laboratories
e+e- collider with 2 separate rings:
s = Mf= MeV
Luminosity up to 1.5×1032 cm-2s-1
2 interaction regions
1. KLOE pb-1
2. DEAR (kaonic atoms) pb FINUDA (hypernuclei) pb-1
KLOE STATUS:
 March 2006: end of KLOE data taking
2500 pb-1 on-peak  8 × 109 f decays
200 pb-1 off-peak (energy scan+1 GeV run)
 Dafne test in progress

3. Initial State Radiation e+e- 
The KLOE physics program:
Kaon physics: CP and CPT violation, CKM unitarity, rare decays, ChPT tests
Hadron physics: lowest mass pseudoscalar, scalar and vector mesons
Hadronic cross-section below 1 GeV: hadronic corrections to g-2
List of the  decays: branching ratios and number of events “on tape”
B.R. Nev KLOE (2.5 fb-1)
K+K  109
K0K0 KSKL  109
 0.15 1.1  109
   107
   106
’   105
(f0(980), ) 3   106
 (a0(980))   105
KK(f0(980), a0(980)) ? ?
Initial State Radiation e+e- 

4. Drift Chamber (He-IsoBut. 2m × 3m)
The KLOE detector:
A large drift chamber
A hermetic calorimeter
A solenoidal superconducting coil
Drift Chamber (He-IsoBut. 2m × 3m)
E.M. Calorimeter (lead-scintillating fibres)
Magnetic field (SuperConducting Coil)
= 0.52 T (solenoid)

5. 2. Results on pseudoscalar mesons.
Results presented here:
2.1 Precision measurement of the  mass
2.2 Improved measurement of the  - ’ mixing
(also f  wp0)
2.3 Dynamics of  3 decays
2.4 Measurement of KS 
2.5 Preliminary measurement of B.R.(-e+e-)
2.6 A flash on 0gg
Talks by:
F.Ambrosino, A.De Santis, B.Di Micco, R.Versaci (Light Meson Spectroscopy I)
M.Martini (Low energy QCD)

6. 2.1 Precision measurement of the mass
Motivated by the discrepancy between the two best measurements:
NA48 (2002) M() = ± ± MeV
GEM (2005) M() = ± ± MeV
( >10 , PDG average gives a scale factor of 5.8 !)
Recently a new measurement has been published by CLEO:
CLEO (2007) M() = ± ± MeV
KLOE method: analysis of fully neutral 3 events
 with 
 with 
3 clusters in the calorimeter only.
Kinematic fit with 4 constraints ==> energies by cluster positions
Discrimination between  and  very easy from Dalitz plot.
Absolute energy scale from the e+e- center of mass energy s
(kinematic fit input) - calibrated comparing M() obtained by the
energy scan to the PDG value (dominated by CMD-2)

7. Systematic error due to:
3 Dalitz plot
 mass peak
KLOE final result:
M() = ± ± MeV
Systematic error due to:
- detector uniformity;
- Dalitz plot cuts.
 mass check:
M() =   0.048
(compatible at 1.5s with PDG)

8. 2.2 Measurement of the h – h’ mixing
KLOE method: measurement of
2002 result (Phys.Lett.B541,45) Lint= 16 pb-1 ,  final states
2007 result (Phys.Lett.B648,267) Lint=427 pb-1 ,  final states
2002
2007
N()
5  107
1.4  109
N()
5  104
1.7  106
N(’)
120
3400 R
(4.70  0.47  0.31) 10-3
(4.77  0.09  0.19) 10-3
BR(’)
(6.10  0.61  0.43) 10-5
(6.20  0.11  0.25) 10-5
P(*)
( )o
(41.4  0.3  0.9)o
Errors are now dominated by “intermediate  and ’ B.R.s”:
(BR(’ ) 3%, BR((’ 5.7%)
(*) evaluated according to A.Bramon et al., Eur.Phys.J. C7, 271 (1999)

9. KLOE analysis uses the constraints:
Constrain to the ’ gluonium content:
KLOE analysis uses the constraints:
J.L.Rosner, Phys.Rev. D27 (1983) 1101,
A.Bramon et al., Phys.Lett. B503(2001) 271
E.Kou, Phys.Rev.D63(2001) 54027
Y1: ’
Y2: ’
Y3: R
Y4: ’
A >3 effect is found:
Z2’ = 0.14  0.04
P = (39.7  0.7)o
R.Escribano, J.Nadal (JHEP 0705,006,2007) reanalyze all V P and P V decays
updating wavefunction overlaps parameters and neglecting the Y1 constraint
 no evidence of gluonium content
Experimentally:
improve (’), BR(’), ’,BR(wp0g)

10. G(wp0g)/G(wp+p-p0)=0.0934±0.0021
e+e-  wp0: interference pattern between f decay and continuum:
fit of cross-section s dependence using 2 decays channels of the w.
Cross-section parametrization:
p+p-p0p0
gp0p0
Preliminary results:
BR(fwp0)=(5.63±0.70)×10-5
G(wp0g)/G(wp+p-p0)=0.0934±0.0021
Using PDG values for the main decay we get:
BR(wp0g)=(8.40±0.19)% (error reduced to 2%, central value shifted –6%)

11. 2.3 Dynamics of the 3 decay
'3 decay  isospin violation in strong interactions mu  md  ms
A test of low energy effective theories of QCD
KLOE has studied with high statistics the dynamics of both channels:
(a)   Dalitz plot analysis: 106 events
(b)   ”slope” analysis: 106 events
(a)    Dalitz plot (submitted to Phys.Lett.B):
- large statistics
- negligible background
- use X and Y variables

12. Fit results of the   Dalitz plot
Including systematic errors
a= 
b=   0.010
d= 
f=  0.01  0.02
Comments:
0. the odd terms (c and e) in X are compatible with 0 (no asymmetries);
1. the quadratic term in X (d) is unambiguosly different from 0;
2. the cubic term in Y (f) is needed to get an acceptable fit;
3. the b=a2/2 (current algebra rule) is largely violated.

13. Dalitz plot asymmetries  test of C invariance
Left-Right C-invariance
Quadrant C-invariance in I=2 amplit.
Sextant C-invariance in I=1 amplit.
(see J.G.Layter et al.,Phys.Rev.Lett.29 (1972) 316)
KLOE results: x 5 statistics respect to best previous experiment
All asymmetries are compatible with 0 up to the 10-3 level

14. (b) Fit results of the   ”slope”
The slope is evaluated by comparing the z distribution of the
data with a Montecarlo simulation with =0 (pure phase space)
 High sensitivity to the M() value (Dalitz plot contour)
MC with M()=547.3
MC with M()=
New (preliminary) result:  = 
 in agreement with Crystal Ball (=-0.0310.004);

15. 2.4 Measurement of the decay KS  
BR estimated by order p4 (G.D’Ambrosio, D.Espriu, Phys.Lett.B175 (1986)27)
KLOE method:   KSKL
- KS tagging provided by KL interacting in the calorimeter:
- Large background from KS   decay (105 times more frequent)
Red= MC signal
Blue= MC background
Points=data
BR(KS  )=(2.27  0.12(stat)  0.05(syst))10-6
Result compared to other experiments and theory

16. 2.5 Preliminary measurement of BR(-e+e-)
-Up to now poorly measured (4 events CMD-2, 16 events CELSIUS-WASA);
program)
BR predicted by ChPT and VMD models (2.63.6 × 10-4);
Plane asymmetry
 “unconventional” CP violation ;
(D.Gao, Mod.Phys.Lett.A17 (2002) 1583)
KLOE preliminary result
based on 622 pb-1 (1/4 of full data sample)
Event selection:
4 tracks events + 1 photon (363 MeV );
Kinematic Fit
p-e recognition (kinematic and calo PiD (in progress))
Backgrounds:
other h decays (mainly and g with g conversion)
charged kaon decays + rp

17. BR(-e+e-)=(2.4 ±0.2stat± 0.4syst) × 10-4
Fit of Minv(ppee) with signal + background
 733±62 signal events (×36 with respect to previous experiments)
Total efficiency = 11.7%
Systematic uncertainty still under evaluation
() data points
signal
other h decays
other bckg (mainly K±)
In progress: asymmetry
 Few % level sensitivity
BR(-e+e-)=(2.4 ±0.2stat± 0.4syst) × 10-4

18. KLOE has presented a 3 signal (only 1/5 of full statistics)
2.6 A flash on  0
ChPT “golden mode”
KLOE has presented a 3 signal (only 1/5 of full statistics)
BR=(22.4±4.6±1.7) ×10-5
4g mass spectrum of selected events
(1.5 fb data).
Yellow = expected bck.
Points = data
The signal is confirmed in
the full data sample.
B.R. updated result with the full
sample will have ~15% error

19. 3. Results on scalar mesons.
KLOE contribution to the understanding of the lowest mass scalars:
f0(980), a0(980), (500)
through radiative decays in pairs of pseudoscalars
 Motivations:
1. f  |ss>  scalar quark composition
of f0(980), a0(980)
2. Search for evidence of (500)
 Results presented here:
3.1 KLOE results on f0(980)pp
3.2 High statistics study of 
3.3 Search for the decay   K0K0
Mass (GeV/c2)
f(1020) 1
f0(980)
a0(980)
k(800)
s(500)
I=0
I=1/2
I=1
Talks by:
S.Fiore, F.Nguyen (Light Meson Spectroscopy II)

20. 3.1 Update of KLOE results on f0(980)
KLOE observed the decay   f0(980) in and 00 channels:
: Phys.Lett.B634 (2006) 148;
: Phys.Lett.B537 (2002) 21; Eur. Phys.J. C49 (2006) 433;
Large “unreducible” backgrounds for both channels:
wp0 and rp0 for p0p0g;
ISR, FSR and rp for p+p-g
Extraction of the scalar amplitude  fit of the spectrum
 parametrization of signal and background
Dalitz plot
f0(980)
mass spectrum

21. Attempt to describe both spectra with a unique scalar amplitude.
[Achasov and Kiselev, Phys.Rev.D73 (2006) ]:
Scalar amplitude = f0(980) + s(600) + interference.
 s(600) parameters and pp/KK scattering phases fixed
(10 different parameter sets, see Eur. Phys.J. C49 (2006) 433)
 free parameters: Mf0, gf0KK , gf0p+p-
Preliminary results (uncertainties under evaluation) are encouraging:
Mf0(MeV)
gf0KK (GeV)
gf0p+p- (GeV)
P(c2)
p0p0g
982.1
4.0
-1.7
6.3%
p+p-g
983.7
4.7
-2.2
2.5%
Comments:
1.The Kaon-Loop well describes the mass spectra;
2.The f0(980) is strongly coupled to the s quark: gf0KK > gf0p+p-
3.The scalar amplitude has a large low mass tail (m<600 MeV) that can be
interpreted as due to the (600);
In progress: combined fit with improved background amplitudes

22. 3.2 High statistics study of   : the a0(980).
“Pure” final state, dominance of a0(980) intermediate state
Selection of:
1.  events with  : fully neutral 5 events;
2.  events with  : 2tracks and 5 events
Background subtraction: 18% in sample 1, 13% in sample 2
Event counting: in sample 1, 3600 in sample 2
Preliminary results on the branching ratio
B.R.(  )(1) = (6.92  0.10stat  0.20syst) 10-5
B.R.(  )(2) = (7.19  0.17stat  0.24syst) 10-5
in good agreement, (part of the systematic errors are common).
Error improvement: 9% (Phys.Lett.B536 (2002) 216)  3% (this result)
M() spectra
Combined fit of the spectra with a0 production parametrizations
(convoluted with efficiencies and resolutions)

23. The fit parameters (preliminary).  Ratio BR( )/BR( )
 BR(  ) contribution
(KL) Kaon-Loop:
(N.Achasov,A.V.Kiselev, Phys.Rev.D73(2006)054029)
 Ma0, couplings ga0KK ga0, phase 
(NS) Breit-Wigner + polynominal
“background”:
(G.Isidori et al., JHEP0605 (2006) 049)
 Ma0, couplings ga0 ga0KK ga0 
KL fit: points =data
red =fitting curve (model  efficiency and resolution)

24. 1. Good consistency between sample 1 and 2:
Comments:
1. Good consistency between sample 1 and 2:
the result is experimentally “solid”;
2. KL fit is stable, NS requires to fix some parameters;
Results:
2.1 ga0KK ~ 2 GeV and ga0KK / ga0 ~ 0.8
 “conflict” with qqqq hypothesis;
2.2 Large values of BR(  ) and of ga0
sizeable coupling with the  (as for f0(980))
Other descriptions:
 Unitarized Chiral Model
[Palomar et al., Nucl.Phys.A729 (2003) 743]
 KK molecule
[Kalashnikova et al., Eur.Phys.J.A24 (2005) 437]
 Linear Sigma Model
[Bramon et al., Phys.Lett.B494 (2000) 221]
Meson
gM (GeV-1) 0
0.13 
0.71 ´
0.75
a0(980)
1.6
f0(980)
1.2 – 2.7

25. 3.3 Search for the decay   KSKS
In  K0K0 the K0K0 pair is:
in a J=0 state  = [|KSKS>-|KLKL>]/2;
in a I=0,1 isospin state  a0 and f0 contribute;
Very small allowed phase space: 2MK < MKK < Msmall B.R.
Predictions on B.R.: from (no scalar contribution) up to 10-7
We have used the decay chain:
 KSKS  ()()
 4 tracks+1 photon (Emax=24 MeV)
Overall efficiency = 20.6%
Very small bckg (ISR KSKL)
Result (preliminary): (Ldt = 1.4 fb-1)
1 event found;
0 expected background;
BR(  KSKS)<1.8 % CL

26. 4. Prospects. (talks by P.Moskal and D.Domenici (Future facilities))
DAFNE is testing now a new scheme to increase luminosity
KLOE phase-2 could start (2009):
 ~10 times more statistics
 improved detector (inner tracker, improved calorimeter
readout,  tagger, new small angle calorimeters)
 “enriched” physics program
Kaon, , ’ decays (high statistics)
   (sigma), 0 2 width
deeply bound kaonic states (AMADEUS proposal)
Increase the center of mass energy up to 2.5 GeV is also
considered (KLOE phase-3)
 physics program extended to
hadronic cross-section (g-2, em)
baryon time-like form factors (DANTE proposal)
 physics (,’,f0(980),a0(980) 2 widths)
[see
F.Ambrosino et al., Eur.Phys.J. C50,729 (2007)]