f 0

Phi Radiative decays at KLOE
Camilla Di Donato*
for the KLOE Collaboration
*Sezione I.N.F.N. Napoli
Outline
Scalar mesons at f-factory:
 f  f0(980)g p+ p- g [PLB634 (2006) 148]
 f  f0(980)g p0 p0 g
Pseudoscalar mesons at f-factory:
 h mass measurement
 BR(f  hg) and mixing angle
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
2
Scalar mesons at a f-factory
How a f-factory can contribute to the understanding of
the scalar mesons
Mass (MeV/c2)
Scalar Mesons Spectroscopy:
f0(980), s(600) and a0(980)
are accessible (k not accessible)
through f  Sg;
Questions:
1. Is s(600) 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 states
Camilla Di Donato
f(1020)
1000
a0(980)
f0(980)
K*0(800)
“k”
500
Novosibirsk, Feb 27 - Mar 2, 2006
f0(600)
“s”
0
I=0
I=1/2
I=1
3
The scalar amplitude description
We use three different approaches in the description of the scalar
amplitude:
1. Kaon-loop KL (Achasov-Ivanchenko, NPB315 1989):
for each scalar meson S there are three free
parameters of the fit: gSpp, gSKK, MS
2. No-Structure NS (by G.Isidori and L.Maiani): a
modified BW + a polynomial continuum: gfSg,
gSpp, gSKK, MS + pol. cont. parameters e+
3. Scattering Amplitudes SA
e(M.E.Boglione, M.R.Pennington, Eur. Phys., J. C30 (2003))
A  (a1+b1m2+c1m4) T(pppp) +
(a2+b2m2+c2m4) T(ppKK)  pole residual gf
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
g
K+
p
S
p
K-
gfKK
gSKK
gSPP
p
V
S
gVSg
gSpp
p
g
4
p+p-g @ large angle: looking for f0
•
e+e-
p+p-g
events with the
photon at large angle (45<g<135)
Events/1.2 MeV
• Main contributions:
– ISR (radiative return to , )
– FSR
M(pp) (MeV)
• Search for the f0 signal as a deviation
of M (p+p-) spectrum from the
expected ISR + FSR shape
• 676,000 events selected (2001+2002)
f0(980) region
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
M(pp) 5(MeV)
Fit to the m(pp) spectrum:
(491 bins, 1.2 MeV wide,
m(pp) = 420 to 1009 MeV)
KL fit
NS fit
Fit : ISR + FSR + p
+ scalar ± interf(SCAL+ FSR)
Kaon-Loop and No-Structure fits:
Good description in both cases
of signal and background
(Kuhn-Santamaria);
“negative” interference;
The introduction of a s(600)
doesn’t improve the fit.
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
6
Scattering Amplitude Fit
gf = 6.6 ×10-4  BR ( ff0 g) × BR ( f0  p+p- ) ~ 3 × 10-5
[similar conclusion from Boglione Pennington 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.
Scattering
gives a Feb
marginal
agreement.
Camilla
Di DonatoAmplitudeNovosibirsk,
27 - Mar 2, 2006
7
Forward-Backward asymmetry
A = (N(q+>90o) – N(q+<90o)) / (N(q+>90o) + N(q+<90o))
p+p- system:
A(ISR)
C-odd
A(FSR) & A(scalar)
C-even
Cross-section: |A(tot)|2 = |A(ISR) + A(FSR) + A(scalar)|2
zoom
FB asymmetry vs. m(pp):
Clear signal ~ 980MeV
 Interesting comparison
with Phokara MC simulation
Data
Simulation FSR+ISR
Simulation FSR+ISR+
scalar(KL)
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
8
p0p0g final state: VMD vs scalar
450 pb-1 from 2001 – 2002 data taking
Two main contributions to p0p0g final state @ Mf:
~ 400k events
fSgp0p0g
√s = 1019.6 MeV
e+e-p0p0p0g
New analysis scheme:
Allow for interference between e+ e-  p0 and f  Sg
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
Bi-dimensional analysis of Dalitz-plot : m(p0p0) vs m(p0g)
9
p0p0g final state: VMD vs scalar
ds  ds 
 ds 
 ds 

+
+





dm  dm VMD  dm  Scalar  dm  interf
•Fit with No-Structure approach: in progress
•Fit Dalitz plot with improved Kaon loop parametrization:
(Achasov Kiselev hep-ph/0512047)
- Insertion of a KK scattering phase
- New parametrization of pp scattering phase
- Scalar contributions: f0(980) and s(600)
- Combined fit to pp scattering data and to already published
KLOE data on fSg gives six sets of parameters able to
describe both distributions
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
10
KLOE preliminary
K-Loop fit: f0+s (dalitz-slices) @ 1019.6 MeV
 Free parameters: Mf0, g_f0p+p-, g_f0K+K-, VMD description
 pp/KK phases and s(600) fixed to Achasov’s results
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
11
KL fit results
• parameter values are from best fit
• The first error is statistical error from fit, the second one
reflects the changes related to the other fit variants with
acceptable c2
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
12
Pseudoscalar mesons at f-factory
●
●
●
h mass measurement;
Br(fhg)/Br(fhg) with p+ p- 7g final state;
Pseudoscalar mixing angle.
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
13
h mass measurement
Large discrepancy between the two
most precise measurements
GEM measurement
Mh = (547.311 ± 0.028 ± 0.032) MeV/c2
Reaction used: p + d → 3He + h
[M. Abdel-Bary et al.,
Phys. Lett. B 619 (2005) 281-287]
NA48 measurement
Using h→3p0 from p- + p → h + n :
Mh = (547.843 ± 0.030 ± 0.041) MeV/c2
[A, Lai et al., Phys. Lett. B 533 (2002) 196]
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
14
Measurement method
Using the decays:
f  hg
f  p0 g
gg
gg
E3
cross checking
purpose
A kinematic fit is performed imposing:
Px,Py,Pz,Etot
t-r/c of clusters
E1
conservation
compatible with light velocity
E2
As a consequence of the kinematic fit the mass measurement is almost
independent from the energy of the clusters, it is dominated by the cluster
positions.
The f momentum and the vertex position are precisely determined run by run
from the study of the Bhabha scattering at large angle e+e-  e+e – (90000
events for each run). Absolute scale determined buy f-line shape and f mass
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
15
Mh measurement @ KLOE
• Kinematic fit applied on f →ggg events
 h and p0 selected by looking at different Dalitz plot regions
c2/ndf = 304/257
p0
p0
h
m = ( 134.956  0.018 ) MeV Mgg (MeV)
s = ( 1.66  0.005 ) MeV
E1<E2<E3
Camilla Di Donato
c2/ndf = 146/161
h
m = ( 547.708  0.014 ) MeV Mgg (MeV)
Novosibirsk, Feb 27 - Mar 2, 2006
16
s = ( 2.143  0.012 ) MeV
Mgg (MeV)
Mp (MeV)
2001-2002 data sample divided into
8 periods, each of 50 pb-1
Mh (MeV)
Mh measurement @ KLOE
547.95
547.90
547.85
547.80
M(p0) = ( 134990  6stat  30syst ) keV
M(p0)PDG = ( 134976.6  0.6 ) keV
547.75
547.70
M(h) = ( 547822  5stat  69syst ) keV
 Systematics mainly from √s and vertex position
- EMC linearity in progress
 NA48 compatibility: 0.24 s
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
17
BR(fhg)/ BR(fhg)
fh'g, h' p+ p-h, hp0
h' p0 p0h, h  p+p-p0
 fhg,
h p0

Signal selection:
charged vertex in a cylinder with a
4 cm radius and a 16 cm height
around the interaction point
7 prompt photons |t – r/c| < 5st and
21 < qg < 159
anti KSKL tag
No way to separate radiative g
Eg (MeV)
and g from p0
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
18
Signal extraction: data 2001-2002
427 pb-1 @ √s = Mf
fh'g, h' p+ p-6g
wrong combination
Nobs = 3750 observed
Nbkg = 345 estim. bkg
Nsig=(Nobs - Nbkg)=3405 ± 65stat ± 28syst
h' mass distribution after wrong
mass combination subtraction
Ks p+ pKl p0 p0 p0
Ks p0 p0
Kl p+ p- p0
Ks p+ p- g
Kl p0 p0 p0
Signal
Camilla Di Donato
Novosibirsk,
Feb(MeV)
27 - Mar 2, 2006
Mhpp
19
Mhpp (MeV)
Results
(
)
0


BR
h

3
p

BR (f  h g ) N
R
 hg
 K
BR (f  hg ) N BRcrg crg + BRntr ntr
hg
h g

(
) (
 BR (h   p p h ) BR (h  p
BRcrg  BR h   p +p -h  BR h  p 0p 0p 0
BRnrt
0
0
+
p p
-
0

)
)
R  (4.74  0.09 stat  0.20 sys ) 10
Source
-3
-5

BR (f  h g )  (6.17  0.12  0.28) 10
Systematics dominated by knowledge of h,h’ branching ratios
Previous KLOE results: Phys. Lett. B541 (2002) 45-51
R  (4.70  0.47 stat  0.31sys ) 10
-3
27 - Mar 2, 2006
(6.10  0Feb.61
BR (f  h g ) Novosibirsk,
 0.43) 10 -5
Camilla Di Donato
Syst. Err.
Filfo-Evcl
1%
TRK
1%
VTX
1%
Back.
Sub.
0.1%
h /h´
0.4%
c2
1.5%
BR”
3%
K
1%
total
4%
20
Mixing angle and h’ gluonic content
Using the Bramon approach (A.Bramon et. al. Eur. Phys. J. C7, 271(1999))
we extract mixing angle:
Rf 

ms Z NS tan V
BR (f  h g )
 cot 2  P 
1



BR (f  hg )
m
Z S sin 2 P





2
 ph 

 p
 h
 P  (41.5  0.3stat  0.7 sys  0.6th )
1
| uu + dd  +Y | ss  + Z | glue 
2
Z2  0  X 2 +Y 2 1
h  X
X 2 + Y 2  0.92  0.06
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
21




3
Conclusions
Extensive study of f0(980) properties with 2001-2002 KLOE data:
• Clear evidence of f  f0 g  p+ p- g both in pp invariant mass
and in the forward-backward asymmetry. Mpp fitted with three
different theoretical approaches: [PLB634 (2006) 148]
• Preliminary results on f  S g  p0 p0 g : fit to Dalitz plot with
improved kaon loop model
Perspectives with our new data sets:
• 2 fb-1 @ Mf: search for f0 / a0  KK
• Energy scan (4 points - 10 pb-1 each - in the 1010-1030 MeV
range): improved study of the √s-dependence of the cross-section
• Off-peak data (~200 pb-1 1000 MeV): search for gg  p0p0
Measurement of h mass: KLOE preliminary result is in agreement with
NA48 measurement
fhg in p+p- + 7 g final state, in agreement with the KLOE previous
Camilla
Di Donato
Novosibirsk,
Feb 27 - Mar 2, 2006
result
in p+p- + 3 g final
state; Pseudoscalar
mixing angle
22
KL fit results: f0+s (the six variants), Sg term
Fixed M, G s
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
23
KL fit results: VDM/Sg compositions
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
24
Fit function: the Achasov parametrization
Camilla Di Donato
Novosibirsk, Feb 27 - Mar 2, 2006
25