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 RR 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