KLOE results on light mesons properties Cesare Bini Sapienza Universita’ and INFN Roma on behalf of the KLOE collaboration ICHEP08, Philadelphia 30/07/2008 Outline: 1.Overview of the KLOE experiment at DAFNE 2.Results on scalar mesons 3.Results on  –  ’ physics 4.Measurement of    0 5.Hadronic cross-section update 6.Conclusions and outlook

1. Overview of the KLOE experiment at DA  NE Frascati Laboratories e + e - collider with 2 separate rings:  s ~ M  = MeV During KLOE run the luminosity has reached the maximum value of 1.5×10 32 cm -2 s -1 in 2005 DAFNE STATUS:  March 2006: end of KLOE data taking 2500 pb -1 on-peak  8 × 10 9  decays 200 pb -1 off-peak (energy scan+1 GeV run);  DAFNE upgrade: test in progress;  New KLOE run starting from mid-2009.

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

2. Results on scalar mesons. The lowest mass scalars: f 0 (980), a 0 (980), f 0 (600)[  ] are accessible through radiative decays in pairs of pseudoscalars  (1020) Mass (GeV/c 2 ) a 0 (980) I=0I=1/2I=1 f 0 (980)  (500)  (800) 0 1 Final states:        f 0 (980),  (500)        f 0 (980),  (500)      a 0 (980)    KK  f 0 (980), a 0 (980) BRs < Motivations: 1.   |ss>  scalar quark composition of f 0 (980), a 0 (980) 2. Search for evidence of   nature of scalar mesons (4q vs. 2q)      : Phys.Lett.B634 (2006) 148;      : Phys.Lett.B537 (2002) 21; Eur. Phys.J. C49 (2006) 433;    : Phys.Lett.B536 (2002) 164.

KLOE observed the decay   f 0 (980)  in      and  0  0 channels:  Large unreducible backgrounds, small signals  Fits of the mass spectra  extraction of signal rate and shape ( parametrizations of signal and bck are required ) f 0 (980)      Dalitz plot      mass spectrum Comments: 1.The Kaon-Loop model (N.Achasov et al.) describes the mass spectra; 2.The f 0 (980) is strongly coupled to the s quark: g f0KK > g f0  +  - 3.The scalar amplitude has a large low mass tail (m<600 MeV) that can be interpreted as due to the  (600).

Recently KLOE has reported a high statistics study of the decay   0   a 0 (980)   Small unreducible background (a 0 (980) dominated)  Combined fit of M(  0 ) spectra in case of    and         data ─ fit ( including efficiency and smearing ) Results: (1) Branching ratio (errors reduced factor ~3) (2) Combined fit: KL = Kaon-Loop fit ( Achasov, Gubin, PRD63(2001) ) NS = No-Structure fit ( Isidori et al., JHEP 0605:049,(2006) ) R  = BR(    /BR(         ) free in the fit (PDG value = 1.73 ± 0.04) KLNS M(a 0 ) (MeV)982.5 ± 1.3 ± (fixed) g aKK (GeV)2.15 ± 0.05 ± ± 0.07 ± 0.28 g a  (GeV)2.82 ± 0.04 ± ± 0.08 ± 0.11 g  a  (GeV -1 )-1.83 ± 0.03 ± 0.08 RR 1.70 ± 0.04 ± ± 0.04 ± 0.01 P(  2 )10%31% NS (  ) (  +    0 )

Br(  0  ) (  ) (  +  –  0 ) Comparison with predictions. (1)Branching Ratios vs several models: Br(  0  0  +  +  –  ) (2) Coupling Ratios compared to simple SU(3) predictions:  qqqq == 4quark model  qq1 == 2quark (f 0 = ss, a 0 = nn)  qq2 == 2quark (f 0 = nn, a 0 = nn) qq: Achasov-Ivanchenko NPB315(1989) Close et al., NPB389(1993) 4q: Achasov-Ivanchenko NPB315(1989) KK molec.: Close et al., NPB389(1993) Achasov et al., PRD56(1997) KK molec.-2: Kalashnikova et al., EPJA24(2005) Palomar et al., NPA729(2003): U  PT Escribano, PRD74(2006): Linear  model KLOEqqqqqq1qq2 (g fKK /g f  )  4.8 >> (g aKK /g a  )   (g fKK /g aKK ) 2 4  No simple conclusion:  f 0 (980) has a large ss component  a 0 (980) has a small or null ss component

Recently has been suggested to include “instantons” to describe light scalar mesons decays [‘t Hooft,Isidori,Maiani,Polosa,Riquer, arXiv ] =c f +c i Adding the instanton term an improved agreement is found between the 4q-model and the measured couplings Prospects in this field: Improve theoretical tools for fitting spectra; Search of  KK  : soon KLOE result (sensitivity )       and    .

3. Results on  -  ‘physics. KLOE contributes to  –  ‘ physics through the radiative decays    BR = 1.2 ×    ’  BR = 6.2 × List of measurements performed and/or in progress: (1)Precision measurement of the  mass (JHEP 12 (2007)073) (2) Improved measurement of the  -  ’ mixing (Phys.Lett.B541(2002) 145) – (Phys.Lett.B648(2007)267) (3) Dynamics of   +     and   3  0 decays (JHEP 0805 (2008)006) (4) Dynamics of   +    decay (5) Measurement of B.R.(    - e + e - ) (6) Measurement of B.R.(  e  e - e + e - ) (7) Observation of  0 

Dynamics of the  3  decay  '  3  decay  isospin violation in strong interactions: m u  m d  m s  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  10 6 events          ”slope” analysis: 0.65  10 6 events          Dalitz plot: - large statistics - negligible background  2dim – fit with the parametrization

Comments: 1. odd terms in X compatible with 0; 2. quadratic term in X (d) unambiguosly  0; 3. cubic term in Y (f) needed to get an acceptable fit; 4. the b=a 2 /2 (current algebra rule) is violated. Results a=  b=   d=  f= 0.14  0.01  0.02 KLOE results: x 5 statistics respect to best previous experiment All asymmetries are compatible with 0 up to the level: No C-violation in  -decays observed.  Analysis of the asymmetries

 Alternative fit of    +  -    including  rescattering (following G.D’Ambrosio et al.,Phys.Rev.D50 (1994)5767) Only 4 free parameters  estimate of   3  0 dynamics  Fit results of the          ”slope” 1dim fit of the z distribution with 1 parameter: .

4. Measurement of    0 OZI and G-parity violating process, large background from e + e -   /  ’   0 Method: measurement of the cross-section  (e + e -   0 ) vs. E c.m. : where Z is the ratio (b)/(a)Data at 1000 < Ec.m. < 1030 MeV         and      analyzed  simultaneous fit, extraction of  Re(Z) and Im(Z) Results: (1) from the fitted value of Z BR(    0 )=(4.4 ± 0.6) ×10 -5 (2) From the ratio between the two channels  (       )/  (         )= ± and finally, using unitarity: BR(         )= (90.24 ± 0.19)% BR(      ) = ( 8.09 ± 0.14)%

5. Hadronic cross-section measurement update  s‘s‘ s KLOE has measured the cross-section  (e + e -   +  - ) for 0.35 < q 2 < 0.95 GeV 2 using the ISR method ( Phys.Lett.B606(2005)12 ) Crucial ingredient for a  = (g-2)/2 “theoretical” evaluation. New measurement on an independent sample (2 x stat.) and with improved analysis strategy:  the new result for a  confirms the previous one: a  (OLD) (0.35 < q 2 < 0.95 GeV 2 ) = (388.7 ± 0.8 stat ± 3.5 sys ± 3.3 th ) × a  (NEW) (0.35 < q 2 < 0.95 GeV 2 ) = (388.2 ± 0.6 stat ± 3.3 sys ± 2.0 th ) × Substancial agreement with BINP results, e + e - vs.  discrepancy is still there For g-2 Theo – Exp = -3.4  is “confirmed”. (J.P.Miller et al., Rept.Prog.Phys.70:795,2007)

6. Conclusions and Outlook DAFNE is testing now a new scheme to increase luminosity The first results are extremely encouraging, work still in progress KLOE phase-2 will start in A program in 3 steps: 1.  ~ 5 fb -1 with present detector + “validation” of the new DAFNE scheme on KLOE; 2.  detector upgrade: new inner tracker,  tagger(s), new small angle calorimeter(s); 3.  KLOE2 Run: the goal is to reach a statistics of 40  50 fb -1 in 3  4 years. KLOE2 Physics Program ( see EoI, ) (1) - Flavour Physics: CKM Unitarity test, Lepton Universality, Search for signals of New Physics, Tests with K S -K L QM-correlated pairs (2) - Low-energy QCD Measurements in the Kaon sector,  and  ’ physics, the low mass scalar mesons,  physics.

Backup slides

List of the  decays: branching ratios and number of events “on tape” B.R.N ev KLOE (2.5 fb -1 )  K + K  10 9  K 0 K 0  K S K L  10 9        0.15  1.1  10 9  1.3   10 7    1.2   10 6  ’  6.2   10 5  (f 0 (980),  ) 3   10 6    (a 0 (980)) 7   10 5  KK  (f 0 (980), a 0 (980)) ? ? Initial State Radiation e + e -           

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

Rare decay:  PT and VDM predictions  BR  3  measurements: CMD-2 ( 4 events ) and ( 16 events ) Non conventional CP violation (non CKM)  plane asymmetry [D.N.Gao MPLA17(2002)]  Measurement of B.R.(  +  ─ e + e ─ ) KLOE preliminary result on a reduced data sample: 622 pb -1 M(  +  ─ e + e ─ ) distribution: fit with signal + background (MC)  733  62 events (global efficiency = 11.7 %) BR(  +  ─ e + e ─ )=(2.4  0.2  0.4)  In progress:  Bckg reduction (        with  conversion)  Full KLOE statistics