International Conference on the Structure and Interactions of the Photon

1
International Conference on the Structure and
Interactions of the Photon

• 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
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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

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KLOE

• Drift chamber
• dp/p lt 0.4
• ?xy?150 ?m ?z?2 mm

• E.m. calorimeter
• sE/E 5.4 / ?(E(GeV))
• st 55 ps/?(E(GeV))?40 ps
• 98 of 4?

Magnetic field 0.52 T
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F radiative decays

• Analysis of 2000 data ? Ldt 16 pb-1
• F ? h?g / hg Phys. Lett. B541 (2002), 45
• F ? p0 p0 g Phys. Lett. B537 (2002), 21
• F ? h p0 g Phys. Lett. B537 (2002), 209

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F radiative decays

• Pseudoscalar mesons (JPC 0-)
• h (547) (I0)
  
• h? (958) (I0)
  
• Scalar mesons (JPC 0)
• f0(980) (I0)
  
• a0(980) (I1)
  

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????? / ????

• The mass eigenstates ?, ?? are related to SU(3)
  octet-singlet
• ?8, ?1 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)

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????? / ????

• ?P can be extracted from the ratio
• (Bramon et al., Eur.Phys.J.C7(1999))
• Br(?????) can probe the gluonic content of ??

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????? / ????

• Decays with ??- 3? final state
• ???????????-?0????0???
  Br ? 3?10-3
• ????? ?????-? ????
  Br ? 2?10-5
• Background from ????-?0 and ??KLKS (with KL
  decaying near the IP)
• Analysis cut
• 1 vertex in IR with 2 tracks
• 3 prompt ? (Egt10 MeV, cos?lt0.93)
• Constrained kinematic fit
• topological cuts on the energy of particles
• ?tot (??) 37
• ?tot (???) 23

????
????
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????? / ????

• Main background is ????
• Selection elliptic cut in the plane of the two
  most energetic photons

Phys. Lett. B 541 (2002), 45
M???? (MeV)
N(???) 120 ?12 ?5 events N(??)
50210 ? 220 events
R Br(?????)/Br(????)
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????? / ????

• Using PDG value for Br(????)
• ? Br(?????) (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 ??
• Consistency check if Z??0 ? Y??cos?P
• other constraints on X?? and Y?? from
• (1) ????????/?(???0??
• (2) ????????/?(?0????

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????? / ????
100 pb-1 (2001)
12
??????pp-7?

• Selection

preliminary
EpEp- (MeV)
N(???) 153 ?12
Br(?????) (7.050.500.53/-0.46)x10-5
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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(??f0?) 5 ? 10-5 3 ?
10-4 10-5 Br(??a0?) 2 ?
10-5 2 ? 10-4 10-5
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Models

• Predictions from Achasov-Ivanchenko,
  Nucl.Phys.B315(1989)

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Scalar mesons (JPC 0)

• f0(980) (I0) f0??0?0????-
  
• a0(980) (I1) a0???
  

• Studied decays (data sample 16 pb-1 from the
  2000 data,5?107?)
• ??f0? f0??0?0 ? 5 ? final state
• ??a0? a0???0 ???? (39)
  ? 5 ?
• ??a0? a0???0 ????-?0 (23) ?
  2 ch. tracks 5 ?
• 
  first observation ?

Previous meas. at VEPP2M
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5 g final states

• 
  cross
  sect.(nb)
• Signal ???0?0? (??f0? ???(500)? ???0?0)
  0.35
• 
  ? ?0?0 ? ?0?
• ????0? (?? a0? ?? ?0?0)
  0.1
• 
  ? ??
• Background ee-???0 ??0?0?
  0.5
• ?????3? (with
  accidental ?s) (17)
• ????? ?0?0?0? (with
  2? lost) (14)
• Sample selection
• exactly 5 prompt photons
• E? gt 7 MeV
• cos? lt 0.93 to avoid the quadrupole
  region
• ?5Ei gt 700 MeV to reject ??KLKS? neutrals

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???0?0?

• Constrained kinematic fit
• to improve resolutions
• Photon pairing
• M?? - M? lt 5?(M?)
• Reject events with
• M?? - M? lt 3?(M?)
• ? 3102 events
• lt?gt 40

1cos2?
Estimated backgr. (20) ee-???0 ??0?0?
339?24 ????0? 166?16 ?????
?0?0?0? 159?12
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Fit to M?? spectrum

• Model
• 1) ??f0? dominated by kaon loop
• (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 ?
• (Gokalp,Yilmaz,Phys.Rev.D64(2001))
• 5) ?? interference term parameterizations
• from Achasov-Gubin, (Phys.Rev.D63(2001))

• Two fits
• Fit A (??f0?) (???0?0 )2
• Fit B (??f0?) (????) (???0?0 )2
• Free parameters Mf0, g2f0KK, g2f0??/g2f0KK,
  g??? and (g???g???)2

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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 g???
0.060 ?0.008

• ( ?? contribution negligible )
• Br(???0?0?) (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)

? Large f0-? destructive interference at M??
lt 700 MeV
Br(??f0?) (4.47 ? 0.21) ? 10-4
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????0? (with ????)
Events

• Constrained kinematic fit
• to improve resolutions
• Photon pairing (1) ?0?0? (2) ??0?
• ? reject ?0?0? events
• M? ? lt 760 MeV (reject f0? events)
• M?? - M? lt 3?(M?)
• ? 916 events lt?gt 32

M?? (MeV/c2)

• Data MC

• Estimated backgr. (30)
• ee-???0 ??0?0? 54?6
• ???0?0? 152?16
• ????? ?0?0?0? 98?10
• ????? ??? 5?2

Br(????0?)(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
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????0? ???-?5? (????-?0)

• No background with the same final state
• Backgr. 2 Tracks 3/4 photons (ee-???0
  ????-?0)
• 
  (???? ????-?0)
• 2 Tracks 6 photons
• (??KSKL???-?0?0?0)
• 1 vertex in IR with 2 tracks
• 5 prompt ? (Egt10 MeV, cos?lt0.93)
• Constrained kinematic fit
• M??-lt 425 MeV (reject KS ? pp-)
• ? 197 events lt?gt19
• estimated backgr. 4?4 events

Br(????0?)(7.96?0.60?0.47) ?10-5
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Fit to Mh? spectrum

• Same model as for the f0 (kaon loop)
• Combined fit, relative normalization fixed
• to Br(????)/Br(????-?0)
• Free parameters
• g2a0KK, ga0??/ga0KK and Br(???0?0???0?)
• Ma0984.8 MeV (PDG) fixed
• ?2/ndf 27.2/25
• g2a0KK/(4?) (GeV2) 0.40 ? 0.04
• ga0??/ga0KK 1.35 ? 0.09
• Br(???0?0???0?) (0.5 ? 0.5) ? 10-5

5?
??-5?
Br(??a0????0?) (7.4 ? 0.7) ? 10-5
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Summary of fit results

• Comparison with predictions from
  Achasov-Ivanchenko, Nucl.Phys.B315(1989)

• f0 parameters are compatible with
  model
• a0 parameters seem not compatible with
  model

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f? f0(980) g / a0(980) g
Phys. Lett. B 537 (2002), 21
Phys. Lett. B 536 (2002), 209
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Conclusions

• First KLOE published papers on f radiative
  decays, 2000 events
• Br(?????) (6.10?0.61?0.43)?10-5
• ?P (41.8 ? 1.7)? (flavor)
• Br(???0?0?) (1.09 ? 0.03 ? 0.05) ? 10-4
• Br(??f0?) (4.47 ? 0.21) ? 10-4
• Br(??a0?) (7.4 ? 0.7) ? 10-5
• Analysis in progress on 20012002 events ?
  500pb-1
• more statistic and models with more free
  parameters

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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.