Impact Parameter Dipole Saturation Model for HERA and nuclear NMC data Henri Kowalski BNLColumbiaDES

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Impact Parameter Dipole Saturation Model for
HERA and nuclear NMC dataHenri
KowalskiBNL/Columbia/DESY Derek
TeaneyBNLhep-ph/0304189St. Petersburg24 of
April 2003
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Impact Parameter Dipole Saturation Model
Proton
b impact parameter
well motivated
Glauber- Mueller dipole cross section
T(b) - proton shape
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t-dependence of the diffractive cross sections
determines the b distribution
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Q2 gt 0.25 GeV2 mu 0.05 GeV mc 1.30 GeV
Fit parameters lg -0.12 C 4.0 Q02
0.8 GeV2 c2/N 0.8
x lt 10-2
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universal rate of growth of all known hadronic
cross-sections
In IP Saturation Model change of l with Q2 is
due to DGLAP evolution effects
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Saturation region --------------------------------
--------------------------------------------------
---------------------
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GBW Model
IP Saturation Model
Saturation radius
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All quarks
Charmed quark
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Gluon density Charm structure
function
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Absolute values of cross sections are strongly
dependent on mc
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Saturation versus Non Saturation
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larger dipoles - more multiple scattering
gt change of proton shape with r
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Density profile
grows with diminishing x and r
approaches a constant value
Saturated State - Color Glass Condensate
S Matrix gt interaction probability
Saturated state high interaction probability
S2 gt 0
multiple scattering
rS - dipole size for which proton consists of
one int. length
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Saturation scale Density scale at the
saturation radius rS
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Saturated state is partially perturbative
cross-sectiom exhibits the universal rate of
growth
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A first glimpse into nuclei
Naïve assumption for T(b) Wood-Saxon like,
homogeneous, distribution of nuclear matter
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Smooth Gluon Cloud
Q2 (GeV2) C 0.74
1.20 1.70 Ca 0.60
0.94 1.40
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Lumpy Gluon Cloud
Q2 (GeV2) C 0.74
1.20 1.70 Ca 0.60
0.94 1.40
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RHIC
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Conclusions We are developing a very good
understanding of inclusive and diffractive gp
interactions The success of the model suggest
that the saturated (perturbative) state plays
an important role at HERA. Saturation is
particularly important in the small x and low Q2
region where the inclusive cross-section exhibits
the universal rate of growth Saturation
effects are considerably increased in nuclei
Revealing the Color Glass Condensate
experimentally would represent a fundamental
advance towards an understanding of high energy
limit of QCD
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? NMC C
? NMC Ca