A1256655917NDXAM

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DPG Tagung München, 24.03.2006
Debora Leone IEKP Universität Karlsruhe
Study of the reaction ee- ? pp- at KLOE

• Introduction
• Result on the small photon angle analysis
  (Phys. Lett. B606, 12 (2005))
• Large photon angle analysis (in progress)
• Conclusion

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Hadronic contribution to (g-2)m
Magnetic momentum
with
amSM amQED amhad amEW
Due to quantum corrections
amhad includes contributions not evaluable in
pQCD, but it can be provided by s(e e- ?
hadrons) by means of dispersion relation
K(s) is a steady function that goes with 1/s,
enhancing low energy contributions of
shadr(s) In energy range lt1 GeV, ee- ? pp-
contributes to more than 60 to amhad
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s(ee- ?pp-) with Radiative Return
DAFNE is designed for a fixed center-of-mass
energy ?s mf 1.02 GeV We can measure
s(ee-?pp-) as a function of the hadronic c.m.
energy M2hadr
(S.Binner, J.H. Kühn, K. Melnikov, Phys.Lett.
B459,1999)
Precise knowledge of ISR process Radiator
function
MC generator Phokhara
(H. Czyz, A. Grzelinska, J.H. Kühn, G.
Rodrigo, hep-ph/0308312)
Radiative Return to ?(w) resonance ee- ? ?(w)
? ? ??-?
This method is a complementary approach to the
energy scan.
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Small photon polar angle analysis
SELECTION

• Pion tracks 50olt ?p lt130o
• Photons ?g lt15o or ?g gt165o
• No photon tagging

KLOE result (140 pb-1 of 2001) Phys. Lett. B606
(2005) 12
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KLOE result compared with CMD-2

• s(ee-?pp-) result
• statistical error negligible
• experimental systematic uncertainty 0.9
• theoretical systematic uncertainty 0.9
• Total systematic error 1.3

• Pion Form Factor comparison
• with result from CMD-2 experiment
• KLOE and CMD-2 in fair agreement

• Dispersion integral evaluation
• KLOE (375.6 ? 0.8stat ? 4.9systtheo) 10-10
• CMD-2 (378.6 ? 2.7stat ? 2.3systtheo) 10-10
• KLOE and CMD-2 in good agreement

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Muon anomaly comparison Theory - Experiment
KLOE and CMD-2 results used to evaluate the
hadronic contribution and therefore the muon
anomaly
Standard model prediction

• KLOE measurement
• Phys. Lett. B606 (2005) 12
• New 4th order QED calculation
• (Kinoshita, Nio)
• Phys. Rev. D70 (2004) 113001
• New Light-by-light calculation
• (Melnikov, Vainshtein)
• Phys. Rev. D70 (2004) 113006

CMD-2 and KLOE averaged in hadronic
contribution DEHZ04 ee-
Theory (SM) - Experiment amexp - amtheo (
25.2 9.2 ) 10-10 2.7 standard deviations
difference
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Large photon polar angle analysis -
signal selection
Pion tracks 50o lt ?p lt 130o Photons at least
one with 50o lt?glt 130o and Eg gt
50 MeV tagged measurement
50oltqplt130o 50oltqglt130o
pp-g MC pp-p0 MC
Mpp2 GeV2
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Reducible background rejection three sources
Radiative Bhabhas ee-? ee- ?, muon pairs ee-?
mm- ? and ????-?0
Particle ID
Radiative Bhabhas are separated by means of a
particle-ID (likelihood function) signature of
EmC-Clusters and time of flight of particles
TrackMass

• To reject mm-g and (partially) pp-p0
• background a cut in the plane Mtrk vs. Mpp2
• is applied. Mtrk is the kinematical variable
• obtained by solving
• under the assumption of ?? x x- ?

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Reducible background rejection Two further
dedicated cuts to pp-p0 rejection
Kinematic fit
Kinematic fit under the pp-p0 background
hypothesis Two tracks in 40? lt ?p lt 140? At least
two photons, one of them with Eg gt 40 MeV and
40? lt ?g lt 140? 4-momenta conservation
Minv(gg) m(p0)
?2
Data pp-g MC
? Angle
?2
Angle between the missing momentum and the
detected photon momentum
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Irreducible background

• mm-g and pp-p0 background channels well
  under control but FSR events as
• ee- ? ppgFSR
• f ? f0 g ? pp g
• f ? r p ? pg p
• all of them with pp-g final state,
  indistinguishable from the signal signature

FSR
rp
f0
Three processes of the same family their
amplitudes interfere
At low Mpp2, ISR and FSR are not the only
contributions to the mass spectrum and to the
charge asymmetry ? model dependence for the
additional contributions
More phenomenological input needed concerning the
hadronic models.
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dN/dMpp2 spectrum

• 50oltqp,glt130o, Eggt50MeV
• Both the particles not identified as
  electrons
• Cut on ?2???
• Cut on TrackMass vs. Mpp2
• Cut on ? angle

The spectrum extends down to the 2-pions threshold
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Forward-backward asymmetry
??- system A(ISR) ? C-odd
A(FSR) ? C-even ? an asymmetry is expected
in the variable
test of sQED via comparison data/MC
f0 KK model f0 no structure afp f0
no structure afp/2 no f0
A(f0)? C-even

20oltqplt160o 45oltqglt135o
Issue to distinguish the effect of the
interference (described in our MC by sQED ) and
the effect of f0(980).
Czyz, Grzelinska, Kühn, Phys.Lett.B 611(116)2006
Mpp GeV
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Forward-backward asymmetry
At large photon angles, the amount of FSR is
large and the interference between the two terms
gives a sizeable effect. KLOE has already
published a first measurement of the
forward-backward asymmetry, and proven the
sensitivity of this quantity to the presence of
scalar mesons.
Phys.Lett.B634 (06), 148
Using the f0 amplitude from Kaon Loop model,
good agreement data-MC both around the f0
mass and at low masses.

• data
• MC ISRFSR
• MC ISRFSRf0(KL)

Mpp (MeV)
Mpp (MeV)
G. Pancheri, O. Shekhovtsova, G.
Venanzoni, hep-ph/0506332
zoom
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Conclusion

• KLOE has measured for the first time the hadronic
  cross section with radiative
• return method, proving the validity of it.
• The measurement of the hadronic cross section in
  a different angular region and
• with tagged photon is in an advanced state.
• The threshold region requires more studies, due
  to the irreducible background
• The analysis on the r-peak and at high Mpp2 is
  close to the conclusion
• ? important check for the already published KLOE
  result.
• Selection cuts are fixed
• Evaluation of efficiencies is almost finished
• test of model scalar QED possible
• study of scalar mesons

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Backup slide
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The KLOE detector at the DAFNE F-factory
Electromagnetic calorimeter
Energy resolution sE/E 5.7/?E(GeV) Time
resolution sT 54 ps/?E(GeV) ? 50 ps
Pb/Scint fibres 4880 PM
Magnetic Field of 0.52 T