1. Recent KLOE results on Hadron Physics
QNP06 – Madrid – 09/06/06
Recent KLOE results on Hadron Physics
Cesare Bini
Universita’ “La Sapienza” and INFN Roma
Outline:
The KLOE experiment at DAFNE
Results on Scalar Mesons
Results on Pseudoscalar Mesons
Prospects for e+e- at Frascati

2. DAFNE: the Frascati f - factory
e+e- collider with 2 separate rings: s = Mf= MeV
2 interaction regions
1. KLOE
2. DEAR (kaonic atoms)
FINUDA (hypernuclei)
Luminosity was delivered
to the 3 experiments
KLOE 2700 pb-1
FINUDA pb-1
DEAR pb-1
Luminosity has increased
up to 1.5×1032 cm-2s-1

3. The KLOE experiment Drift Chamber (He-IsoBut. 2m × 3m)
The 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)
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)

4. Physics at a f – factory: a window on the lowest mass mesons
Sketch of the f decays:
Main decay channels
Branching fraction
 K+K-
49.2 %
KSKL
34.0 %
 rp + p+p-p0
15.3 %
 hg
1.301 %
 p0g
0.125 %
 h’g
6.2 × 10-5
 p0p0g
1.1 × 10-4
 hp0g
8.3 × 10-5
+ “radiative return” to p+p-
(1020) 
a0(980)
f0(980) 
' KK 
0-+
1--
0++ 
r(770)
Direct decay
Radiative decay
p-emission
#events = Br.F. × 8 × 109  ~105 h’, pp, hp

5. Overview of KLOE physics
(1) Kaon physics: several “fundamental physics” items:
Extraction of the Vus element of the CKM matrix from
5 semi-leptonic decays of neutral and charged kaons
 test of CKM Unitarity
 CPT tests: first measurement of KS semi-leptonic asimmetry
Kaon interferometry in p+p-p+p- final states:
 bounds on quantum decoherence + CPT violation
Reduced upper bound on KS  p0p0p0 CP violating decay
Precision measurement of KS  p+p- / KS  p0p0
Measurement of KL and KS  gg  ChPT test
~ 450 pb-1 analysed
= 20 × previous analyses
(2) Hadron physics:
 Scalar Mesons ( a0(980), f0(980) s(500) )
 Pseudoscalar Mesons ( p0, h, h’ )
 Vector Mesons ( properties of r(770), w(780) )
(3) Measurement of the Hadronic Cross-Section below 1 GeV
 hadronic corrections to g-2

6. How a f-factory can contribute to the understanding of
Scalar Mesons
How a f-factory can contribute to the understanding of
the scalar mesons
Mass (GeV/c2)
f(1020)
Scalar Mesons Spectroscopy:
f0(980), s(500) and a0(980)
are accessible (k not accessible)
through f  Sg;
Questions:
1. Is s(500) needed to describe
the mass spectra ?
2. “couplings”of f0(980) and
a0(980) to f  |ss> and to KK,
pp and hp.
 4-quark vs. 2-quark vs. KK molecule 1.
f0(980)
a0(980)
k(800)
s(500) 0.
I=0
I=1/2
I=1

7. Scalar Mesons with KLOE
 f0(980)g  p+p-g
 p0p0g
 K+K-g [ 2m(K)~m(f0)~m(f) ]  expected BR ~ 10-6
 K0K0g “ “ ~ 10-8
 a0(980)g  hp0g
 K+K-g expected BR ~ 10-6
 K0K0g  “ ~ 10-8
 s(500)g  p+p-g
 p0p0g
General Comments:
 fits of mass spectra are needed to extract the signals: this requires a parametrization for the signal shape;
 the unreducible background is not fully known: a parametrization is required and some parameters have to be determined from the data themselves;
 sizeable interferences between signal and background;

8. The p+p-g analysis P.L.B 634 ,148 (2006)
Event selection:
2 tracks with qt>45o; missing momentum qpp>45o (large angle)
Each track is pion-like (tracking, ToF and Shower shape)
1 photon matching the missing momentum
 6.7 ×105 events / 350 pb-1
Particle identification: p vs. e and m
(Likelihood: Tof and Shower shape)
pions, muons
(“trackmass”)
muons
pions
electrons

9. The p+p-g final state is dominated by: Initial State Radiation
Final State Radiation
The f0(980) is observed as a “bump” in:
ds/dm(pp) vs. m(pp)
Ac vs. m(pp) -- Forward-Backward asymmetry
f0(980) signal
Events Ac
data
MC no f0
MC with f0
m(pp) (MeV)

10.  “Large” coupling to the f
Fit of the mass spectrum using 2 different models for the scalar amplitude:
 Kaon-Loop model [N.N.Achasov et al. ] mf0, gf0p+p-, gf0K+K-,
 “No Structure” model [G.Isidori et al. ] mf0, gf0p+p-, gf0K+K-, gff0g, b0,b1
Free parameters: scalar amplitude + background
An acceptable fit
is obtained with
both models:
P(c2)(KL)=4.2%
P(c2)(NS)=4.4%
Mass values ok
 gf0K+K-> gf0p+p-
 “Large” coupling to the f
B.R.(f  f0(980)g  p+p-g) = 2.1  2.4 × 10-4 (from integral of |Amplitude|2)

11. The p0p0g analysis Event selection:
5 photons with qg>21o ; no tracks;
Kinematic fit  energy-momentum conservation;
Kinematic fit  p0 masses: choice of the pairing.
 4 ×105 events / 450 pb-1  analysis of Dalitz-plot
2 components in the Dalitz-plot

12. Fit of the Dalitz-plot (without rejecting wp0) using the same 2 models:
 Improved Kaon-Loop model (introducing the fs(500)g)
 “No Structure” model
Parameters: mass and couplings ( mf0, gf0p+p-, gf0K+K-, gff0g) + background
The s(500) parameters are fixed. The fit is repeated by changing them
2-dim fit shown
slice bt slice.
A good fit
is obtained with
both models:
P(c2)(KL)=14%
P(c2)(NS)= 4%

13. Fit results
f0(980) param.
NS model
KL model
mf (MeV)
981 ÷ 987
976 ÷ 987
gffg (GeV-1)
2.5 ÷ 2.7 -
gfp+p- (GeV)
1.3 ÷ 1.4
1.4 ÷ 2.0
gfKK (GeV)
0.1 ÷ 1.0
3.3 ÷ 5.0
R=g2fKK /g2fp+p-
0. ÷ 0.9
3.0 ÷ 7.3
Comments:
 s(500) is needed in KL fit [p(c2) ~ 10-4  14% !]
(best s parameters are: M=462 MeV, G=300 MeV);
 f0(980) parameters agree with p+p-g analysis KL fit
again R > 1 (gf0KK > gf0p+p-);
 NS fit gives large gff0g but R<1 (??);
 BR extracted:  integral of |scalar amplitude|2
BR( p0p0g) ~ 1/2 × BR(p+p-g): neglecting KK, we add the 2 BRs
 BR(f  f0(980)g) = (3.1 ÷ 3.5) × 10-4
 G(f  f0(980)g) = 1.2 ÷ 1.6 keV

14. The hp0g analysis
Simultaneous analysis of hgg and hp+p-p0 channels:
Pts. = data 450 pb-1 = 20 × published results, hist = KL fit
The spectra are dominated by the a0 production
(negligible unreducible backgrounds).
Work in progress, results soon

15. Scalar Mesons: Summary and Outlook
Complete analysis of f  f0(980)g with f0(980)  p+p- and p0p0
 good description of the scalar amplitude with KL model:
 large couplings to Kaons: hint of a large s-quark content
 s(500) is still required to describe the p0p0 Dalitz-plot
 NS fit suggests large coupling of f0(980) to the f
2) Work in progress to:
 make a combined analysis of f0(980)  p+p- and p0p0
 complete the analysis of f  a0(980)g with a0(980)  hp0  study the decay chain f  [f0(980)+a0(980)]g  KKg
(expected sensitivity down to 10-8)
3) Further studies:
 search for e+e-  e+e-p0p0 events (gg  p0p0 ) using the
s = 1 GeV (off-peak = less background);
search for the s(500) [F.Nguyen et al. 2005]

16. Pseudoscalar Mesons  9 ×106 p0  4 ×105 h’
Large samples of p0, h and h’ through the radiative decay f  Pg
 8 ×107 h
 9 ×106 p0
 4 ×105 h’
List of the analyses done or in progress
Measurement of the h (and p0) masses
 this talk
Measurement of the h – h’ mixing angle in p+p- 3g
Phys.Lett.B541 (2002) 45
Measurement of the h – h’ mixing angle in p+p- 7g
Dynamic of the decay h  p+p-p0
AIP:Conf.Proc.814:463,2006
Dynamic of the decay h  p0p0p0
Measurement of the BR(h  p0gg)
Upper limit on the C-violating decay h  ggg
Phys.Lett.B591 (2004) 49
Upper limit on the P(CP)-violating decay h  p+p-
Phys.Lett.B606 (2005) 276
Study of the decay h  p+p-e+e-
in progress
Upper limit on the P(CP)-violating decay h  p0p0

17. Measurement of the h (and p0) masses
2 recent measurements done with different techniques:
GEM (COSY) p+d  3He+h  M(h)=( ± 28 ± 32) keV/c2
(missing mass technique)
NA48 (CERN) p-+p n+h  M(h)=( ± 30 ± 41) keV/c2
(h  3p0 reconstruction)
8 s discrepancy: dM(h)=(532 ± 41 ± 52) keV/c2 (errors added in quadrature)
KLOE: ;  check with 0; 0
Technique: kinematic fit mostly based on photon positions and timing;
 energy-momentum and vertex position from large angle Bhabha scattering
3g Dalitz-plot
The p0 and the h peak are well defined p0 h
Mass (MeV)

18. Results (still preliminary):
The statistical uncertainty is ~negligible
Systematic uncertainties from knowledge of s and vertex position
(work in progress to reduce it)
The p0 mass is well in agreement with PDG value
M(p0) = (  6stat  30syst ) keV
M(p0)PDG = (  0.6 ) keV
The h mass is in agreement with NA48 and in disagreement with GEM
M(h) = (  5stat  69syst ) keV
KLOE
NA48
GEM (see QNP06)
h mass (MeV)

19. Measurement of the h – h’ mixing angle in p+p- 7g
Method: measurement of
using similar h and h’ decay chains
Previous analysis: h’  p+p-h h  gg  p+p-3g
h  p+p-p0 p0  gg  p+p-3g
This analysis: h’  p+p-h h  p0p0p0  p+p-7g
h’  p0p0h h  p+p-p0  p+p-7g
h  p0p0p0 p0  gg  7g
427 pb /2002 data
N(hg) =  (no bck)
N(p+p-7g’s) = 375060
(Nbckg= 345)
 N(h´g) = 3405 ± 61stat ± 28syst
h’ signal (~10% bck)
h signal (no bck)
The systematic uncertainty is due to the uncertainty on the intermediate BRs

20. Pseudoscalar mixing angle: extracted using the parametrisation
[A.Bramon et al. 1999]
Mixing angle
(2) Analysis of h’ gluonic content:
[E.Kuo, 2001]
Before KLOE results
Including new KLOE result
X2+Y2 = 0.93 ± 0.06

21. Prospects for e+e- physics at Frascati
Short term program:
 New FINUDA Run – 2007
previous statistics × 5
 SIDDHARTA Run – 2008
upgraded version of DEAR
(see C.Curceanu QNP06)
 ??? > 2009
Discussions are open in the laboratory about a possible
continuation of a low-energy e+e- program
Present project == DANAE (not approved yet):
 higher luminosity f – factory (L~1033 cm-2s-1)
 energy scan: √s = 1 ÷ 2.5 GeV (L~1032 cm-2s-1)

22.  Kaon physics + h / h’ physics @ f AMADEUS
3 Expressions of Interest have been presented:
KLOE2
 Kaon physics + h / h’ physics @ f
 gg physics + hadronic cross-section up to 2.5 GeV
AMADEUS
 deeply bound f
DANTE
 baryon time-like form factors (√s > 1.9 GeV)
Waiting for the final decision of the laboratory.
Any contribution is welcome !

23. Spare Slides

24. Scalar Mesons Renewed interest after B-factory results:
new scalar meson “zoology” above 2.3 GeV
 reconsider the low mass spectrum
A 0++ meson arises from a qq pair in a
triplet spin state (S=1) and P-wave (L=1)
Assuming 2 quarks interacting by a single gluon
exchange, other configurations are found [Jaffe 1977]:
 Color triplet diquarks and anti-diquarks
Attractive interaction between diquark and anti-diquark
giving a color singlet
 it is possible to build up 4-quarks scalar meson

25. Provided s and k are there
Analysis of the mass spectra of the lowest mass mesons
Pseudoscalar multi-plet
Vector multi-plet
Scalar multi-plet:
s(500), k(700), f0(980), a0(980)
Provided s and k are there
the scalars have an
“Inverted Spectrum”

26. Inverted Mass spectrum  hint of a 4q picture
Building Rule:
Mass
Q=0 Q=0 Q= Q=-1 (the f0(980)
and a0(980))
add 2
Quarks s
Q= Q= Q=0 Q=-1 (the k(800))
add 1
Quark s
I3=0 Q=0 (the s(500))
2 important consequences: if 4q hypothesis is correct
 the s(500) and the k(800) have to be firmly established
 the s-quark content of f0 and a0 should be sizeable
( f0 and a0 couplings with f (ss) and with kaons
[N.N.Achasov and V.Ivanchenko 1989]

27. Definition of the relevant couplings (S=f0 or a0):
S to f gfSg (GeV-1)
S to kaons gSKK=gSK+K-=gSK0K0 (GeV)
f0 to pp (I=0) gf0pp=√3/2 gf0p+p-=√3 gf0p0p0 (GeV)
a0 to hp (I=1) ga0hp (GeV)
Coupling ratio Rf0=(gf0K+K-/ gf0p+p-)2
Ra0=(ga0K+K-/ ga0hp)2 K+ K- p+ p- g
Kaon-loop
No-structure
f0,a0 f