DANTE: DAnae Nucleon Time-like form factor Experiment Status and Plans

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DANTE DAnae Nucleon Time-like form factor
ExperimentStatus and Plans

• Marco Mirazita

LNF Scientific Committee Frascati, 27 november
2006
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Nucleon Form Factors and QCD

• QCD has been extensively tested in the high
  energy domain
• asymptotic freedom ? perturbative calculations
  (at percent level)
• QCD at low energy is much more complicated
• non-perturbative methods (lattice, chiral
  theory, )
• no completely satisfactory agreement with data

Nucleon FF are fundamental quantities describing
the internal structure of the nucleon from low
(charge and magnetization distributions) to high
Q2 regimes (valence quark distributions) -
simplest non pQCD observables in the hadronic
physics - their calculation includes all the
complications of the non-pQCD regime
A succesfull non perturbative QCD model must be
able to reproduce nucleon FF in all the q2 plane
Nucleon FF are also important for all process
where nucleons are involved - GPDs - strange
content of the nucleon - neutrino experiments
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Nucleon EM Form Factors
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Proton FF in the SL region
JLab measurement with polarization transfer
technique in ep ? ep scattering

• 2-photon exchange contributions?
• Quark angular momentum?

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Science Technology Review
DOE ST review was held June 2006.
Excerpts from the Executive Summary
Electromagnetic Form Factors
V. Burkert, CLAS Collaboration Meeting, 11/02-04
2006
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FF in the Time-like region
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An important tool DR
Time-like Form Factors HAVE TO BE MEASURED
(polarization)
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FF measurement in TL region
Phases extraction from polarization measurements
No beam polarization needed
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FF measurement projected accuracy

• Projected results at 5 beam energies, 100pb-1 per
  each value
• finer energy scan with lower statistics can be
  done
• e(n)40-50 of the KLOE calorimeter
• ? neutron and proton with comparable errors

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Polarization measurement
Based on secondary scattering in strong
interaction process
Analizing power
Unpolarized cross section
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Proton Polarimeter
http//www.lnf.infn.it/conference/nucleon05/FF/pol
arimeter_study_2.pdf
Counting rate is determined by the convolution
of - multiple scattering (small angle,
Molière) - strong nuclear scattering (large
angle, exp. unpol. cross section and analyzing
power)
Higher analyzer thickness ? higher
rate but - larger Molière angle qm - lower
tracking resolution
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Proton Polarimeter
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Scattering angle distributions
12 qp bins of 15
Good events for polarization measurement qc lt qs
lt 40
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Polarimeter acceptance
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Azimuthal angle distributions

• Fit of angular distributions
• N(?scat) p1
• (1Accos?scat Assin?scat)
• ?Py ?Px

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Polarization extraction
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Polarimeter thickness
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Conclusions and outlook

• PROTON measurement feasible
• - modulus very high precision from threshold up
  to the highest beam energy can be easily
  integrated with other measurements of the high
  energy program
• - phase measurement with good precision
  dedicated run required (polarimeter)
• NEUTRON measurement feasible
• - modulus statistical error comparable to the
  proton
• - phase high neutron detection efficiency makes
  easier the measurement

NEXT STEPS - detailed study of the inner
detector region with the polarimeter - neutron
polarimeter