Transcript Experimental Measurement of the F meson radiative decays into scalars and pseudoscalars mesons The KLOE Coll.

Experimental Measurement
of the F meson radiative
decays into scalars and
pseudoscalars mesons
The KLOE Coll. presented by
Camilla Di Donato I.N.F.N. Naples
International Conference on the
Structure and Interactions of the Photon
KLOE data collected
1999 run :
2.5 pb-1
machine and detector
studies
2000 run : 25 pb-1
7.5x107 f
published results
2001 run: 190 pb-1
5.7x108 f
analysis in progress
2002 run: 300 pb-1
9.0x108 f
analysis in progress
KLOE
Drift chamber:
• dp/p < 0.4%
• xy150 m ; z2 mm
E.m. calorimeter:
• E/E = 5.4% / (E(GeV))
• t = 55 ps/(E(GeV))40 ps
• 98% of 4
Magnetic field: 0.52 T
F radiative decays
•Analysis of 2000 data:  Ldt = 16 pb-1
F  hg / hg
F  0 0 g
F  h 0 g
Phys. Lett. B541 (2002), 45
Phys. Lett. B537 (2002), 21
Phys. Lett. B537 (2002), 209
F radiative decays
Pseudoscalar mesons (JPC= 0-+)
• h (547)
• h (958)
(I=0)
(I=0)
Scalar mesons (JPC= 0++)
• f0(980)
• a0(980)
(I=0)
(I=1)
fhg / fhg
• The mass eigenstates h, h are related to SU(3) octet-singlet
h8, h1 through the mixing angle P
• Recent studies based on PT and phenomenological analyses
suggested a two mixing angle scenario
• In the quark flavour basis the two mixing angles are almost equal
 mixing is described by only one parameter (P)
η  cos P
η  sin  P
1
uu  dd  sin  P s s
2
1
uu  dd  cos P s s
2
fhg / fhg
• P can be extracted from the ratio
(Bramon et al., Eur.Phys.J.C7(1999)) :
 m s tg V   p η 
Br(f  ηγ)
2
  
R
 cotg  P  1 
Br(f  ηγ)
m sin2 P   p η 

2
3
 ms


;
 1.45 
m



• Br(fhg) can probe the gluonic content of h
η  X η
1
2
u u  d d  Yη s s  Z η glue
fhg / fhg
• Decays with +- 3g final state:
fhg ; h+-0 ; 0gg
fhg ; h+-h ; hgg
Br  310-3
Br  210-5
Background from f+-0 and fKLKS (with KL decaying near the IP)
Analysis cut:
• 1 vertex in IR with 2 tracks
• 3 prompt g (E>10 MeV, |cos|<0.93)
• Constrained kinematic fit
• topological cuts on the energy of particles
tot (hg) = 37 %
tot (hg) = 23 %
fhg
fh´g
fhg / fhg
• Main background is fhg
• Selection: elliptic cut in the plane of the two most energetic photons
Phys. Lett. B 541 (2002), 45
Mgg (MeV)
N(hg) = 120 12
N ηγ5
ε ηγevents;
Br(η  π  π  π 0N(hg)
) Br(π 0 =50210
γγ)  220 events
R
N ηγ ε ηγ Br( η  π π η) Br(η  γγ)


R = Br(fhg)/Br(fhg)
 (4.70  0.47  0.31)  10
Fρ 
3
• F =0.95 (interference with e+e-h(hg )
fhg / fhg
• Using PDG value for Br(fhg):
 Br(fhg) = (6.100.610.43)10-5
• Pseudoscalar mixing angle:
P = (41.8  1.7) (flavor)
 P = (-12.9 1.7) (octet-singlet)
•Gluonic content of h:
η  X η
1
2
u u  d d  Yη s s  Z η glue
Consistency check: if Zh=0  |Yh|=cosP
other constraints on Xh and Yh from:
(1) hg/(0g
(2) hgg/(0gg
X2η  Yη2  0.940.06
0.09
(2)
(1)
fhg / fhg
Mgg (MeV)
fhg7g
dN/dE
• Selection:
Ks  0 0
Kl  0
Ks  g
Kl  000
data
2000
2001
2002
Eg (MeV)
N(hg) = 153 12
Ks  0 0
Kl  0
Ks  g
Kl  000
data
E++E- (MeV)
E++E- (MeV)
Br(fhg) = (7.05±0.50+0.53/-0.46)x10-5
f f0 980 g / a0 980 g
•The scalar mesons f0 (980) a0 (980) are not easily interpreted
as qq states
•Jaffe(1977) suggested qqqq states
•Weinstein, Isgur (1990) suggested KK molecule
•Both BR and scalar mass spectra are sensitive to nature
Br(ff0g)
Br(fa0g)
qq
5  10-5
2  10-5
qqqq
3  10-4
2  10-4
KK
10-5
10-5
Models
• Predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989)
ss(uu  dd)/ 2
f0 model
g2f0KK/(4)
2.3
(GeV2)
(=g2a0KK/4)
gf0 /gf0KK
0.3—0.5
Br(f00g)104
~1
a0 model
g2a0KK/(4)
(GeV2)
ga0h/ga0KK
Br(f a0g)104
(uu  dd)/ 2
ss
0.15
0.3
(=g2a0KK/4)
(=2g2a0KK/4)
2
~ 0.15
ss(uu  dd)/ 2
2.3
(=g2f0KK/4)
0.91
~2
0.5
~ 0.2
(uu  dd)/ 2
0.15
(=g2f0KK/4)
1.53
~ 0.2
Scalar mesons (JPC= 0++)
• f0(980) (I=0)
• a0(980) (I=1)
f000 +a0h
• Studied decays (data sample: 16 pb-1 from the 2000 data,~5107f)
ff0g ; f000  5 g final state
Previous meas.
at VEPP2M
fa0g ; a0h0
hgg
(39%)  5 g
fa0g ; a0h0
h+-0 (23%)  2 ch. tracks +5 g
first observation

5 g final states
• Signal: f00g (ff0g ; f(500)g ; f00)
 00
 0g
fh0g (f a0g ; f 00)
 hg
• Background: e+e-0 00g
fhg3g (with accidental g’s)
fhg 000g (with 2g lost)
cross sect.(nb)
~ 0.35
• Sample selection:
– exactly 5 prompt photons
– Eg > 7 MeV
– |cos| < 0.93
to avoid the quadrupole region
– 5Ei > 700 MeV to reject fKLKS neutrals
~ 0.1
~ 0.5
(~17)
(~14)
f00g
• Constrained kinematic fit
to improve resolutions
• Photon pairing
• |Mgg - M| < 5(M)
• Reject events with:
|Mg - M| < 3(M)
 3102 events
<> = 40%
Estimated backgr. (~20%)
e+e-0 00g 33924
fh0g
16616
fhg 000g
15912
1+cos2
g
0

0
Fit to M spectrum
radiative g
f
• Model :
1) ff0g dominated by kaon loop
K+
f0
K-
0
0
gfKK
gf0KK
gf0
(Achasov-Ivanchenko, Nucl.Phys.B315(1989))
2) f0 propagator with finite width corrections
3) (500) B-W with M=478 MeV and =324 MeV
(Fermilab E791-Phys.Rev.Lett.86(2001)770)
4) point-like coupling of (500) to f
(Gokalp,Yilmaz,Phys.Rev.D64(2001))
5)  + interference term parameterizations
from Achasov-Gubin, (Phys.Rev.D63(2001))
• Two fits:
Fit A : | (ff0g) + (f00 )|2
Fit B : | (ff0g) + (fg) + (f00 )|2
Free parameters: Mf0, g2f0KK, g2f0/g2f0KK, gfg and (gfgg)2
Fit results
A
B
2/ndf
109.5/33
43.2/32
Mf0 (MeV) 9624
973 1
g2f0KK/(4) 1.290.14 2.79 0.12
(GeV2)
g2f0KK/g2f0 3.220.29 4.000.14
gfg
—
0.060 0.008
(  contribution negligible )
Br(f00g) = (1.09  0.03  0.05)  10-4 (Fit B)
(SND: (1.220.10 0.06)  10-4 ; CMD-2: (1.080.170.09)  10-4)

-4
Br(ff
g)=
(4.47

0.21)

10
0
Large f0- destructive interference at M < 700 MeV
• Estimated backgr.: (~30%)
e+e-0 00g
546
f00g
15216
fhg 000g
9810
fhg ggg
52
Mh (MeV/c2)
Events
• Constrained kinematic fit
to improve resolutions
• Photon pairing: (1) 00g ; (2) h0g
 reject 00g events
• M  < 760 MeV (reject f0g events)
• |Mgg - Mh| < 3(Mh)
 916 events
<> = 32 %
Events
fh0g (with hgg)
• Data
—MC
Br(fh0g)=(8.510.510.57) 10-5
SND :(8.8 1.40.9)  10 –5 ;CMD-2: (9.0 2.41.0)  10 –5
cos
fh0g +-5g (h+-0)
• No background with the same final state
• Backgr.: 2 Tracks + 3/4 photons (e+e-0 ; +-0)
(fhg ; h+-0)
2 Tracks + 6 photons
(fKSKL+-000)
• 1 vertex in IR with 2 tracks
• 5 prompt g (E>10 MeV, |cos|<0.93)
• Constrained kinematic fit
• M+-< 425 MeV (reject KS  
 197 events
<>=19%
estimated backgr. 44 events
Br(fh0g)=(7.960.600.47) 10-5
Fit to Mh spectrum
• Same model as for the f0 (kaon loop)
• Combined fit, relative normalization fixed
to Br(hgg)/Br(h+-0)
• Free parameters:
g2a0KK, ga0/ga0KK and Br(f00h0g)
Ma0=984.8 MeV (PDG) fixed
2/ndf
27.2/25
g2a0KK/(4) (GeV2) 0.40  0.04
ga0h/ga0KK
1.35  0.09
Br(f00h0g) (0.5  0.5)  10-5
Br(fa0gh0g)= (7.4  0.7)  10-5
5g
+-5g
Summary of fit results
• Comparison with predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989)
KLOE
ss(uu  dd)/ 2 (uu  dd)/ 2
ss
f0 model
g2f0KK/(4)
2.790.12
2.3
0.15
0.3
(GeV2)
(=g2a0KK/4)
(=g2a0KK/4)
(=2g2a0KK/4)
gf0 /gf0KK
0.500.01 0.3—0.5
2
0.5
Br(f00g)104 1.090.07
~1
~ 0.15
~ 0.2
a0 model
g2a0KK/(4)
(GeV2)
ga0h/ga0KK
Br(f a0g)104
ss(uu  dd)/ 2
0.400.04
2.3
(=g2f0KK/4)
1.350.09
0.91
0.740.07
~2
(uu  dd)/ 2
0.15
(=g2f0KK/4)
1.53
~ 0.2
• f0 parameters are compatible with q q q q model
• a0 parameters seem not compatible with q q q qmodel
f f0980 g / a0980 g
Phys. Lett. B 537 (2002), 21
2001+2002 data
2000 data
Phys. Lett. B 536 (2002), 209
M (MeV)
Mh0 (MeV)
Conclusions
First KLOE published papers on f radiative decays,
2000 events:
• Br(fhg) = (6.100.610.43)10-5
• P = (41.8  1.7) (flavor)
•
•
•
Br(f00g) = (1.09  0.03  0.05)  10-4
Br(ff0g) = (4.47  0.21)  10-4
Br(fa0g) = (7.4  0.7)  10-5
Analysis in progress on 2001+2002 events  500pb-1:
more statistic and models with more free parameters
==================================================
==== Author : KLOE Collab. (Speaker: Camilla Di Donato) Type :
Experimental Measurement of the Phi meson radiative decays
into scalars and pseudoscalars mesons.
The Kloe experiment has measured the radiative decays of the
Phi meson into pi0, eta and eta'(958); these measurements are
relevant to assess the mixing in the pseudoscalar nonet as well as
to evaluate the gluon content in the eta'(958). Moreover also the
radiative decays into pi0 pi0 gamma and eta pi0 gamma have
been measured. These decays are dominated by the final states
f0(980) and a0(980). The measurement of the branching ratios
and of the pi0-pi0 or eta-pi0 invariant mass spectrum helps to
understand the controversial nature of the above scalar mesons.
==================================================