KLOE results on light mesons properties
Cesare BiniSapienza Universita’ and INFN Romaon behalf of the KLOE collaboration
ICHEP08, Philadelphia 30/07/2008
Outline:1. Overview of the KLOE experiment at DAFNE
2. Results on scalar mesons3. Results on – ’ physics4. Measurement of 0
5. Hadronic cross-section update6. Conclusions and outlook
1. Overview of the KLOE experiment at DANE
DAFNE @ Frascati Laboratories• e+e- collider with 2 separate rings:
s ~ M= 1019.4 MeV
• During KLOE run the luminosity has reached the maximum value of 1.5×1032 cm-2s-1 in 2005
DAFNE STATUS:
March 2006: end of KLOE data
taking
2500 pb-1 on-peak 8 × 109
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)
)(%4.5GeVEE
E ps
GeVEps
t 130)(
55
%4.0)(
p
p
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: f0(980), a0(980), f0(600)[] are accessiblethrough radiative decays in pairs of pseudoscalars
(1020)
Mass (GeV/c2)
a0(980)
I=0 I=1/2 I=1
f0(980)
(500)
(800)
0
1
Final states:f0(980), (500)
f0(980), (500) a0(980)KKf0(980), a0(980) BRs < 10-4
Motivations: 1. |ss> scalar quark composition
of f0(980), a0(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 f0(980) in and 00 channels: Large unreducible backgrounds, small signals Fits of the mass spectra extraction of signal rate and shape
(parametrizations of signal and bck are required)
f0(980)Dalitz plot
mass spectrum
Comments:1.The Kaon-Loop model (N.Achasov et al.) describes the mass spectra;2.The f0(980) is strongly coupled to the s quark: gf0KK > gf0+-
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 a0(980)Small unreducible background (a0(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)
BR( 0) (7.050.08stat 0.21syst )10 5
(2) Combined fit:KL = Kaon-Loop fit (Achasov, Gubin, PRD63(2001)094007)NS = No-Structure fit (Isidori et al., JHEP 0605:049,(2006) )
R = BR(/BR() free in the fit(PDG value = 1.73 ± 0.04)
KL NS
M(a0) (MeV) 982.5 ± 1.3 ± 2.7
982.5 (fixed)
gaKK (GeV) 2.15 ± 0.05 ± 0.17
2.01 ± 0.07 ± 0.28
ga(GeV) 2.82 ± 0.04 ± 0.12
2.46 ± 0.08 ± 0.11
ga(GeV-
1)- 1.83 ± 0.03 ±
0.08
R 1.70 ± 0.04 ± 0.05
1.70 ± 0.04 ± 0.01
P(2) 10% 31%
NS()
(+0)
Br(0)
()
(+–0)
Comparison with predictions.(1)Branching Ratios vs several
models:
Br(00++–)
(2) Coupling Ratios compared tosimple SU(3) predictions:
qqqq == 4quark model qq1 == 2quark (f0 = ss, a0 = nn) qq2 == 2quark (f0 = nn, a0 = 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): UPT Escribano, PRD74(2006): Linear model
KLOE qqqq qq1 qq2
(gfKK/gf)2 4.6 4.8 >> 1 >>1 0.25
(gaKK/ga)2 0.6 0.7 1.2 1.7 0.4 0.4
(gfKK/gaKK)2 4 5 1 2 1
No simple conclusion: f0(980) has a large ss component a0(980) has a small or null ss component
(S)Oc(S)Oc(S) 1Iffdec L
Recently has been suggested to include “instantons” to describe light scalar mesons decays [‘t Hooft,Isidori,Maiani,Polosa,Riquer, arXiv0801.2288]
=cf +ci
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 10-8) and .
3. Results on - ‘physics.
KLOE contributes to – ‘ physics through the radiative decays
BR = 1.2 × 10-2
’ BR = 6.2 × 10-5
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 30 decays (JHEP 0805 (2008)006)
(4) Dynamics of + decay (5) Measurement of B.R.(-e+e-)(6) Measurement of B.R.(ee-e+e-)(7) Observation of 0
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
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=a2/2 (current algebra rule) is violated.
Resultsa=-1.090 0.005 +0.008 -0.019
b= 0.124 0.006 0.010d= 0.057 0.006 +0.007 -0.016
f= 0.14 0.01 0.02
KLOE results: x 5 statistics respect to best previous experimentAll asymmetries are compatible with 0 up to the 10-3 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 30 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. Ec.m.:
where Z is the ratio (b)/(a)Data at 1000 < Ec.m. < 1030 MeV and analyzedsimultaneous fit, extraction of Re(Z) and Im(Z)
Results: (1) from the fitted value of ZBR( 0)=(4.4 ± 0.6) ×10-5
(2) From the ratio between the two channels( )/( )=0.0897 ± 0.0016and finally, using unitarity:BR( )= (90.24 ± 0.19)%BR( ) = ( 8.09 ± 0.14)%
5. 5. Hadronic cross-sectionHadronic cross-section measurement measurement updateupdate
s‘s
KLOE has measured the cross-section(e+e- +-) for 0.35 < q2 < 0.95 GeV2
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 < q2 < 0.95 GeV2) = (388.7 ± 0.8stat ± 3.5sys ± 3.3th) × 10-10 a(NEW) (0.35 < q2 < 0.95 GeV2) = (388.2 ± 0.6stat ± 3.3sys ± 2.0th) × 10-10
Substancial agreementwith BINP results,e+e- vs. discrepancy is still thereFor g-2Theo – 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 luminosityThe first results are extremely encouraging, work still in progressKLOE phase-2 will start in 2009.
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, http://www.lnf.infn.it/lnfadmin/direzione/roadmap/LoIKLOE.pdf) (1) - Flavour Physics: CKM Unitarity test, Lepton Universality, Search for signals of New Physics, Tests with KS-KL 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. Nev KLOE (2.5 fb-1)
K+K- 0.49 3.7 109
K0K0 KSKL 0.33 2.5 109
0.15 1.1 109 1.3 10-2 9.7 107
1.2 10-3 9.0 106
’ 6.2 10-5 4.6 105
(f0(980), ) 3 10-4 2.5 106
(a0(980)) 7 10-5 4.6 105
KK(f0(980), a0(980)) ? ?
Initial State Radiation e+e-
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 < Msmall B.R.Predictions on B.R.: from 10-13 (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)<1.810-8 90% CL
• Rare decay: PT and VDM predictions BR 3 10-4
• 2 measurements: CMD-2 (4 events) and WASA@CELSIUS (16 events)• Non conventional CP violation (non CKM) plane asymmetry
[D.N.Gao MPLA17(2002)]
Measurement of B.R.(Measurement of B.R.(++──ee++ee──))
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) 10-4
In progress:Bckg reduction ( with conversion)Full KLOE statistics