Diapositiva 1

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Scalar Mesons Physics with the KLOE detector
C.Bini Universita La Sapienza and INFN
Roma For the KLOE collaboration
Outline 1. Status of the KLOE experiment 2.
Hadron Physics at a f - factory 3. Scalar
Mesons at a f - factory 4. Results 4.1
pp-g 4.2 p0p0g 4.3 hp0g 5. Summary and
perspectives
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1) Status of the KLOE experiment
These days end of f peak run ? 2 fb-1 collected
in the last two years.
ANALYZED
Program now energy scan around the f off-peak
run ?s 1 GeV KLOE end by spring 2006
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2) Hadron Physics at a f - factory
Preview analysis done and in progress (non Kaon
physics)
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3) Scalar Mesons at a f - factory
How a f-factory can contribute to the
understanding of the scalar mesons
Scalar Mesons Spectroscopy f0(980), f0(600)
and a0(980) are accessible (k not
accessible) through f ? Sg Questions 1. Is
f0(600) needed to describe the mass spectra
? 2. couplingsof f0(980) and a0(980) to f ?
ssgt and to KK, pp and hp. ? 4-quark vs.
2-quark states
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How to detect these radiative decays

• ? f0(980)g ? pp-g
• ? p0p0g
• ? KK-g 2m(K)m(f0)m(f) ? expected BR
  10-6
• ? K0K0g 10-8

• ? a0(980)g ? hp0g
• ? KK-g ?expected BR 10-6
• ? K0K0g ? 10-8

• ? f0(600)g ? pp-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
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How to extract the signal

• 1. Electric Dipole Transitions
• ? G(E1) ? Eg3 Mif(Eg)2
• 2. Distortions due to KK
• thresholds (Flatte-like).

Kaon-loop (by N.N.Achasov) for each scalar
meson S gSpp, gSKK, MS No-Structure (by
G.Isidori and L.Maiani) a modified BW a
polynomial continuum gfSg, gSpp, gSKK, MS
pol. cont. parameters Scattering Amplitudes (by
M.E.Boglione and M.R.Pennington) A ?
(a1b1m2c1m4) T(pp?pp) (a1b1m2c1m4)
T(pp?KK) ? pole residual gf
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Definition of the relevant couplings (Sf0 or a0)
S to f gfSg (GeV-1) S to
kaons gSKKgSKK-gSK0K0 (GeV) f0 to pp
(I0) gf0ppv3/2 gf0pp-v3 gf0p0p0 (GeV) a0 to
hp (I1) ga0hp (GeV) Coupling
ratio Rf0(gf0KK-/ gf0pp-)2 Ra0(ga0KK-/
ga0hp)2
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The unreducible backgrounds
Unreducible backgrounds (pp- ) huge
backgrounds Initial state radiation
(ISR) Final state radiation (FSR) f ?rp
with r ? pg (p0p0) large backgrounds ee-
? wp0 with w ? p0g f ?r0p0 with r 0 ?
p0g (hp0) small backgrounds ee- ? wp0 with w
? hg f ?r0p0 with r 0 ? hg
(pp-) vs. (p0p0) search for the same
amplitude with a completely different
background ! (hp0) is the cleanest sample
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4.1) The pp-g analysis
I - Event selection (a) 2 tracks with qtgt45o
missing momentum qppgt45o (Large Angle) (b)
Each track is pion-like (tracking, ToF and Shower
shape) (c) 1 photon matching the missing momentum
Particle identification p vs. e and m
(Likelihood Tof and Shower shape)
pions, muons
electrons
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II The data sample 6.7 105 events / 350 pb-1
_at_ vs Mf 2.2 104 events / 11 pb-1 off-peak
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III - Fit to the m(pp) spectrum (491 bins, 1.2
MeV wide, 420 to 1009 MeV) F ISR FSR rp
scalar interference
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Parameter uncertainties are dominated by the
systematic errors

• Comments
• Mass value OK PDG 980 10 MeV
• R gt 1 in both fits (in agreement with published
• values p0p0g)
• KL couplings gtgt NS couplings effect of
  polynomial
• continuum
• NS suggests large coupling to the f (see
  following)

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Scattering Amplitude Fit
gf 6.6 10-4 ? BR(f?f0(980)g)
BR(f0(980)?pp-) 3 10-5 similar conclusion
from BP analysis of p0p0g data (KLOE SND)
Summarizing The peak at 980 MeV is well
interpreted in both KL and NS approaches as due
to the decay f ? f0(980)g with a negative
interference with FSR. The couplings suggest the
f0(980) to be strongly coupled to kaons and to
the f. No space for f0(600). Scattering Amplitude
gives a marginal agreement.
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IV - The Forward-Backward asymmetry A
(N(qgt90o) N(qlt90o)) / sum pp- system
A(ISR) C-odd A(FSR) A(scalar)
C-even Cross-section A(tot)2 A(ISR)2
A(FSR)2 A(scalar)2 2ReA(ISR) A(FSR)
2ReA(ISR) A(scalar) 2ReA(FSR) A(scalar)
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FB asymmetry vs. m(pp) ? Clear signal 980
MeV ? Interesting comparison with simulation
Data Simulation FSRISR Simulation FSRISR
scalar(KL)

• The simulation provides a qualitative
  description of
• f0(980) region behaviour (the signal is
  reproduced)
• Low mass behaviour (low mass tail of the signal.
• Remarkable result not a fit but an absolute
  prediction

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V Cross section dependence on vs Absolute
prediction based on KL fit parameters
Data on-peak Data off-peak
KL absolute prediction Based on fit parameters
Concluding remark pp-g is a powerful tool to
test scalar production mass spectrum, FB asym.
and ?s dependence KLOE has now collected 2 fb-1
at f ? factor 6 more. Is now starting a finer
energy scan around the f
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4.2) The p0p0g analysis
I - event selection 5 photons with qggt21o no
tracks Kinematic fit ? energy-momentum
conservation Kinematic fit ? p0 masses choice
of the pairing. ? 4 105 events / 450 pb-1
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• New analysis scheme
• Removed the m(w) cut wp0 are now in the sample
• 2. Bi-dimensional analysis Dalitz-plot m(p0p0)
  m(p0g)
• New treatment of systematics pairing
  problem...
• Improved VDM parametrization of wp0

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II Fit of the Dalitz plot (still preliminary
results) KL and NS fits in progress
Residuals vs. DP position
Data- fit comparison (on projections)
Comments 1. VDM part still not perfect (see
residuals) 2. Scalar part ok BUT f0(600) is
still needed in KL fit p(c2) 10-4 ? 30
! 3. f0(980) parameters agree with pp-g
analysis again R gt 1 (gfKK gt gfpp-).
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4.3) The hp0g analysis
I The data samples out of 400 pb-1
Statistics of PLB536 (2002) 209 20

• (h ? gg) Improved reducible
• background subtraction
• 2.2 104 events ½ are signal

(h ? pp-p0) almost background free ? 4100
events bck lt 3
Red signal Other colors bck
Full pts. 20 pb-1 data Empty pts. 400
pb-1 data
M(hp) (MeV)
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II The combined fit
Simultaneous fit of h?gg and h?pp-p0 channels
ratio of BR is fixed Pts. data, hist fit
(including smearing)
KL fit
NS fit
The spectra are dominated by the a0 production
both models are able to reproduce them
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Preliminary results of the fits (KL and NS)

• Comments
• gfa0g in agreement with f0 value
• Ra0 0.78 (KL) and 0.74 (NS) lt 1

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5) Summary and Perspectives
The KLOE scalar analysis is not yet completed.
However

• f0(600) required in the p0p0 channel not in
• the pp- one no clear answer by now.
• 2. Couplings
• both NS and KL fits indicate
• Rf0 (gf0KK-/ gf0pp-)2 2 4
• Ra0 (ga0KK-/ ga0hp)2 0.7 0.8
• from NS analysis large couplings to the f
• gff0g 1.2 2.0 GeV-1
• gfa0g 1.9 GeV-1 (unc. evaluation in progress)
• in any case gtgt gfpg gfhg gfhg (0.1 ? 0.7
  GeV-1).

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KLOE perspectives on scalar mesons
1. Conclude analysis on 2001-2002 data sample
for f0(980) (neutral final states) and
a0(980). 2. With 2000 pb-1 _at_ f peak
improvement expected for f0 ? pp-
combined fit pp- AND p0p0 search for f0, a0 ?
KK 3. With new forthcoming energy scan
data improved study of the vs-dependence of
the cross-section Off-peak test run of gg
? p0p0