KLOE results on light mesons properties

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