Analysis of HERA Data

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Analysis of HERA Data
HERA observations Diffraction in DIS is a
leading twist Fast rise of the total g p
cross section with energy at larger Q2 Slow
(hadronic like) rise at low Q2 Vector Meson
production (access to the dynamic in the b
space) Jet, Charm, Bottom production Particle
multiplicities, Energy Flows..

• H. Kowalski
• Columbia, NY, February 2002

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Papers J.Bartels, J.Ellis, H.Kowalski, M.
Wuesthoff , EPJ-C7 443 (1999)K.
Golec-Biernat, M. Wuesthoff , Phys.Rev. D59
(1999) 014017 H. Kowalski. M. Wuesthoff,
Liverpool 2001-DIS 192 A. Caldwell, M. Soares,
Nucl. Phys. A696 (2001) 125 J.Bartels,
H.Kowalski , EPJ-C19 693 (2001)J.Bartels, K.
Golec-Biernat, H.Kowalski, in preparation
(2002)
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HERA Interactions
Collisions of e (e-) of 27.5 GeV with p of
920 GeV
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Diffraction in DIS
Diffraction Incoming proton remains intact after
the scattering and carry more than 99 of its
momentum. How is it possible that the incoming
proton remains intact ? Confinement forces drag
the cloud back into a few outgoing
hadrons Dynamics of diffraction at HERA can be
described by few Feynman diagrams extrapolated to
the nonperturbative limit (aligned jets).
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Total gp Cross Section
Proton Rest
Frame incoming virtual photon fluctuates into a
quark-antiquark pair which in turn emits a
cascade-like cloud of gluons
Transverse size of the quark-antiquark cloud is
determined by r 1/Q 2 10-14cm/ Q (GeV)
Successive emission of gluons leads to rise of
the cross section with W
DGLAP gt
l is a measure of the radiation intensity
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Dipole description of DIS
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GBW Model K. Golec-Biernat, M. Wuesthoff
Size of r determined by the wave
function perturbative region r ltlt
2R0 saturation region r gtgt 2R0
Saturation radius
from DIS data sqq x-0.3 in the
perturbative region gt Assumption
Parameters fitted to DIS data s0 23 mb l
0.29 x0 0.0003
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Parameters fitted to HERA DIS data c2 /N 1
s0 23 mb l 0.29 x0 0.0003
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Diffractive Measurement in DIS
xIP is fraction of protons momentum carried by
the gluon cloud (pomeron) b is fraction of
pomerons momentum carried by the struck quark
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Saturation Model Predictions for
Diffraction
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Approximate relationships
Note maxz(1-z) 1/4
symmetric aligned
(suppression for rgtgt1/Q)
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Saturation Effects
The rise of the cross section with energy cannot
continue forever when the gluon density of a
single cascade becomes too high a second cascade
develops
the pairwise (coherent) interaction of cascades
with the proton leads to negative interference
which damps the growth of the cross section
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DGLAP evolution in the Saturation Model
In the Saturation Model for small r
Dipole cross section in the small-r region
Modification of the model
with xg(x, ) evolving according to DGLAP
equations from
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Fits to new data
mq 140 MeV Original GBW Saturation
Model c2/N 2.4 Saturation Model with
evolution c2/N 1.2
s0 23 mb l 0.28 A0.029 C 0.26 Q02
0.5 GeV2
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Fits to new data
mq 0 Saturation Model with
evolution c2/N 1.0
s0 23 mb l 0.0 A 0.098 C 1.0 Q02
1.0 GeV2
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Inclusive Diffraction Mx- Method
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Inclusive Diffraction LPS - Method
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Dipole Cross Section
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Gluon Amplitude f(x,l2) in the Saturation Model
Dipole cross section in momentum space
Doing the angular integration
Approximating
we find for large l2
f(x,l2) coincides with the un-integrated gluon
distribution
Saturation without evolution
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mq 140 MeV
mq 0 MeV
saturation
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