Topical%20Seminar%20on%20Frontier%20of%20Particle%20Physics%202004:%20QCD%20and%20Light%20Hadrons

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Topical Seminar on Frontier of Particle
Physics 2004 QCD and Light Hadrons Lecture 3
Wei Zhu East China Normal University
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Outline of Lecture Three
Small x Physics

• Introduction
• Modified DGLAP Equations
• JIMWLK Equation
• Phenomenology of Saturation
• A Geometric Nuclear Effect

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1. Introduction
Color Glass Condensation
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From saturation scale QS2, QCD evolution is
stopped
Saturation Scale
DGLAP
MD-DGLAP
JIMWLK
TRUE ?
Qs2 ?
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2. Modified DGLAP Equations
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Left The solid (dotted) curves are the results
of the MD-DGLAP equation with (without)
antishadowing corrections. The dashed curves are
the results of the DGLAP equation with the
GRV98LO. Notice that the solid and dashed curves
have opposite concavities. Right As Left but
for the sea quark distribution in the proton.
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LeftThe Q2 dependence of the gluon distribution
in proton at fixed values of x. The solid
(dotted) curves correspond to with (without)
antishadowing corrections. The dashed cuves are
the results of the DGLAP equation with the
GRV98LO. Right As Left but for the sea quark
distribution function in proton.
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3. JIMWLK Equation
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Unfortunately, nobody knows the correct solution
of the JIMWLK equation except its zero-order
solution.
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4. Phenomenology of Saturation
The distribution of partons in the transverse
plane.
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The recombination cross-section for gluon with
transverse momentum Q is roughly given by
the number of such gluons per unit of transverse
area is given by
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is the probability that the dipole does not have
an inelastic interaction as it passes through the
nucleus
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quark saturation momentum
gluon saturation momentum
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a maximum occupation number for quarks
Some Predictions
The CGC approach for nucleus - nucleus collision
with the saturation of parton density.
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Geometrical scaling
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5. A Geometric Nuclear Effect
Twist-4, as-order, tree approximation, FT
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Twist-4, as-order, tree approximation, FL
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a time-space picture of FT
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Time-space pictures of FT
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Time-space pictures of FL
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Qiu-Vitev Resummation
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Scale for cold matter power corrections

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Factorization
Saturation
Nuclear Effect
Evolution equation
Structure Function