Probing small x gluon with low mass Drell-Yan dilepton

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A prediction of unintegrated parton distribution
Ruan Jianhong
Zhu Wei
East China Normal University
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outline

• Introduction

• The models

• Our scheme

• Conclusion

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1 Introduction
? The integrated parton distributuion

• evolution according to DGLAP equation, input
  parton distribution such as GRV,MRST,CTEQ

• can be used to describe inclusive processes

• well decided by the global fit of structure
  function F2

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? the unintegrated parton distribution
For less inclusive processes, the distributions
unintegrated over the tranverse momentum have to
be considerd.
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2 The models
? CCFM evolution equation

• The unintegrated gluon distribution satisfies the
  CCFM evolution equation based on angular ordering.

• The interactions among initial partons are
  neglected in the CCFM equation.

• The solution of the CCFM equation has only proved
  practically with Monte Carlo generators.

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? Golec-Biernat-Wusthoff gluon distribution

• Based on the parametrization of the
  dipole-nucleon cross section with parameters
  fitted to the HERA data

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? Kharzeev-Levin gluon distribution

• based on the idea of gluon saturation, the gluon
  distribution is parametrized.

• It was claimed that the gluon distribution
  leads to a good description of the recent RHIC
  rapidity distributions.

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? KMR scheme

• Kimber, Martin and Ryskin proposed that the two
  scale UPDFs can be derived from the single-scale
  unintegrated distribution, and its dependence on
  the second scale µ is introduced by using the
  Sudakov factor.

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3 Our method KMR scheme

• MD_DGLAP
• equation

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the initial quark and gluon densities (GRV-like)
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• our result

The unintegrated gluondensity in proton at µ10
GeV
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The unintegrated gluondistributions in Pb(A208)
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Comparison of our predicted (RZ)-gluon(solid
curves) with other models
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Published in physics review c 80,045209(2009)
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Particle multiplicities and limiting fragmentation
? Two component model
?central region
gg ?g mechanism
quark recombination model
? fragmentation region
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?central region
? fragmentation region
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Proton-proton collisions
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? Fragmentation limiting
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5 Conclusion
? we predict the unintegrated parton
distributions in proton and nucleus by using the
KMR scheme incorporating the shadowing and
antishadowing corrections
?We find that the suppression of the unintegrated
gluon distribution when kt? 0 arises from the
valence-like input rather than the nonlinear
saturation effect, although the nonlinear
shadowing effect is obvious.
?We use two complementary production mechanisms
hard gluon-gluon fusion in the central rapidity
region and soft quark recombination in the
fragmentation region to study the particle
multiplicity distributions in hadron-hadron
collisions at high energies.
?We find that the limiting fragmentation
hypothesis, which generally appear in present
data of hadron collisions is partly violated if
the observations are across over a wide range
between the RHIC-LHC energies.
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Thank You!