1. KLOE results on hadron physics
MENU07, Julich 11/09/2007
KLOE results on hadron physics
Cesare Bini
Università “La Sapienza” and INFN Roma
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
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)
 December June 2007: FINUDA run
 Now: machine tests and preparation of SIDDHARTA (kaonic atoms) run

3. 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)
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

4. 2. Results on pseudoscalar mesons.
The lowest mass pseudoscalar mesons (JPC=0-+) are accessible
at a  - factory through the decays:
B.R. Nev KLOE (2.5 fb-1)
K+K  109
K0K0 KSKL  109
   107
   106
’   105
Results presented here:
2.1 Precision measurement of the  mass
2.2 Improved measurement of the  - ’ mixing
2.3 Dynamics of  3 decays
2.4 Measurement of KS 
2.5 Other analyses in progress (, -e+e-)

5. 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 presented 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

6. Systematic error due to:
3 Dalitz plot
 mass peak
KLOE final result:
M() = ± ± MeV
Systematic error due to:
- space uniformity;
- Dalitz plot cuts.
 mass check:
M() =   0.048
(well compatible with PDG value)

7. 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)

8. 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 and J.Nadal (JHEP 0705,006,2007) reanalyze all V P and P V decays
updating wavefunction overlaps parameters ==> no evidence of gluonium content
Experimentally:
improve (’), BR(’), ’measurements

9. 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:
  Dalitz plot analysis:
1.34 106 events
  ”slope” analysis:
0.65 106 events

10. 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.
According to B.Borasoy and R.Nissler (Eur.Phys.J.A26 (2005) 383)
it is difficult to accomodate such a small b value in a ChPT approach

11. 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

12. 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 value of M() (Dalitz plot contour)
MC with M()=547.3
MC with M()=
New result:  = 
==> in agreement with Crystal Ball (=-0.0310.004);

13. 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  0.13(stat) (syst))10-6
Result compared to other experiments and theory

14. 2.5 Others (2 flashes on other ongoing KLOE analyses)
  +-e+e-: signal observed:
1500 events expected with 2.5 fb-1
   0: ChPT “golden mode”
3 signal (only 1/5 of full statistics)
Updated B.R. result soon
with 15% statistical error
signal confirmed in full data sample.
Few % sensitivity on plane asymmetry
(CP violation, D.Gao, Mod.Phys.Lett.A17 (2002) 1583)

15. 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
 S   (I=0)f0  
  (I=0) f0 
  (I=1) a0
 K+K- (I=0,1) f0 a0
 K0K0  (I=0,1) f0 a0
Mass (GeV/c2)
f(1020) 1
f0(980)
a0(980)
k(800)
Motivations:
1. f  |ss> scalar quark composition
2. Search for evidence of (500)
s(500)
Results presented here:
3.1 Review of KLOE results on f0(980)
3.2 High statistics study of (preliminary)
3.3 Search for the decay   K0K0 :
I=0
I=1/2
I=1

16. 3.1Review of KLOE results on f0(980)
KLOE has 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;
FB asymmetry
Dalitz plot
f0(980)
mass spectrum
Fit results:
1.The Kaon-Loop well describes the mass spectra;
2.The f0(980) is strongly coupled to the s quark: gf0KK > gf0p+p-, gf0is large
3.The scalar amplitude has a large low mass tail (m<600 MeV) that can be
interpreted as due to the (500) (not clear results yet);

17. 3.2 High statistics study of   : the a0(980).
“Pure” final state, expected 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
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 two spectra with a0 production parametrizations
(convoluted with efficiencies and resolutions)

18.  Ratio BR( )/BR( )
The fit parameters.
 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)

19. 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 hypothesys (not for f0(980));
2.2 Large values of BR(  ) and of ga0
sizeable coupling with the  (as for f0(980))
Meson
gM (GeV-1) 0
 0.13 
 0.71 ´
 0.75
a0(980)
 1.6
f0(980)
1.2 – 2.7

20. 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 can 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 : (Ldt = 1.4 fb-1)
1 event found;
0 expected background;
BR(  KSKS)<1.8 % CL

21. 4. Prospects.
The DAFNE team 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)
The possibility to 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)]

22. Conclusions:
Hadron Physics is an important part of the KLOE
program;
Many results have been obtained;
Others are to come:
full data sample to be analysed
more channels not yet analysed

23. SPARES