Polarized parton distribution

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Ali. N. Khorramian (IPM),
Institute for studies in theoretical Physics and
Mathematics
Physics Department, Semnan University
Workshop on Low-x physics 16-19 September 2002
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Polarized Structure Function

• Workshop on Low-x physics
• 16-19 September 2002

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Ali. N. Khorramian (IPM),
Institute for studies in theoretical Physics and
MathematicsPhysics Department, Semnan
Universitykhorramiana_at_theory.ipm.ac.irS.
Atashbar Tehrani Physics Department, Persian
Gulf Universityatashbar_at_cic.aut.ac.ir
Workshop on Low-x physics 16-19 September 2002
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• Outline
•   I. Valon model
•        II. Unpolarized and polarized valon
  
• distribution  
•       III. Polarized parton distributions
•       IV. Proton and Neutron polarized
  
• structure functions.
  
•   V. Summary Outlook

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Some experimental data for p, n, d
E80, 130 (p) E142 (n) E143 (p, d)
E154 (n) E155 (p, d)     EMC, SMC
(p, d)     HERMES (p, d, n)
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F. Arash and Ali N. Khorramian Nucl. Phys. B 99,
164 (2001)
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What is the valon model?The valon model
describes the hadron structure relevent for
multiparticle production.The polarized valon is
defined to be a dressed valence quark in QCD with
the cloud of polarized gluons and sea quarks
which can be resolved by high Q2 probes. At
sufficiently low value of Q2 the internal
polarized structure of a valon cannot be resolved
and hence it behaves as a polarized valence
quark. For example in the proton we have 2
U-valons and one D valon.
  I. Valon model
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• Unpolarized Valon distribution in a proton
• To facilitate the phenomenological analysis Hwa
  assumed a simple form for the exclusive valon
  distribution in unpolarized proton which is
• Where yi is the momentum fraction of the i-th
  valon.
• The single valon distributions are obtained by
  integration

R. C. Hwa and C. B. Yang , hep-ph /0202140
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Unpolarized valon
U
U
D
  F. Arash and Ali N. Khorramian Nucl. Phys. B
99, 164 (2001)   Ali N.
Khorramian, F. Arash , Structure of Hadrons,
Proceedings of the International Workshop XXIX on
Gross Properties of Nuclei and Nuclear
Excitations Hirschegg, Austria, (2001)
R. C. Hwa and M. S. Zahir, Phys. Rev. D 23,
2539 (1981)
R. C. Hwa and C. B. Yang , hep-ph
/0202140
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Polarized Valon distribution in a proton
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Unpolarized and polarized valon distribution in a
proton
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Polarized valon distribution in a proton
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For calculating the LO and NLO evolutions of the
spin-dependent parton distributions, we have
used the well known analytic LO and NLO solution
in Mellin n-moment space with the n-th moment
being defined by
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III.
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LO
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Moments of polarized parton distributions
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Polarized parton distributions as a function of x
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NLO
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Moments of polarized parton distributions in LO
and NLO
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    IV. Proton and Neutron polarized
structure
functions.
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Polarized structure function in LO
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Polarized structure function in NLO
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• The compare of our predictions for polarized
  proton structure function from
• our model with the measured structure functions
  in experiments on proton target.

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The compare of our predictions for polarized
proton structure function from our model with
the measured structure functions in experiments
on proton target.
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Plots of neutron polarized structure function
against x at Q2 2, 3
GeV2
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• Plots of neutron polarized structure function
  against x
• at Q2 5 GeV2

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conclusion

• We have presented a model that be used for
  extraction polarized parton distributions.
• Our results for polarized proton and neutron
  structure functions are good agrement with
  available experimental data.

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