577 research outputs found
Parton distribution function for quarks in an s-channel approach
We use an s-channel picture of hard hadronic collisions to investigate the
parton distribution function for quarks at small momentum fraction x, which
corresponds to very high energy scattering. We study the renormalized quark
distribution at one loop in this approach.
In the high-energy picture, the quark distribution function is expressed in
terms of a Wilson-line correlator that represents the cross section for a color
dipole to scatter from the proton. We model this Wilson-line correlator in a
saturation model. We relate this representation of the quark distribution
function to the corresponding representation of the structure function
F_T(x,Q^2) for deeply inelastic scattering
Testing saturation with diffractive jet production in deep inelastic scattering
We analyse the dissociation of a photon in diffractive deep inelastic
scattering in the kinematic regime where the diffractive mass is much bigger
than the photon virtuality. We consider the dominant q\bar{q}g component
keeping track of the transverse momentum of the gluon which can be measured as
a final-state jet. We show that the diffractive gluon-jet production
cross-section is strongly sensitive to unitarity constraints. In particular, in
a model with parton saturation, this cross-section is sensitive to the scale at
which unitarity effects become important, the saturation scale. We argue that
the measurement of diffractive jets at HERA in the limit of high diffractive
mass can provide useful information on the saturation regime of QCD.Comment: 12 pages, 5 figures, misprints corrected, published versio
Color Glass Condensate and BFKL dynamics in deep inelastic scattering at small x
The proton structure function F_2(x,Q^2) for x < 0.01 and 0.045< Q^2 < 45
GeV^2, measured in the deep inelastic scattering at HERA, can be well described
within the framework of the Color Glass Condensate.Comment: 4 pages, 1 figure, incl. IOP style files. Talk given at the 17th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(Quark Matter 2004), Oakland, CA USA, 11-17 Jan 200
Political conservatism, need for cognitive closure and intergroup hostility
Two studies examined the interaction of political conservatism and the need for cognitive closure in predicting aggressiveness in intergroup conflict and hostility toward out-groups. In the first study, Polish participants indicated their preference for coercive conflict strategies in the context of a real-life intergroup conflict. Only among participants who identify themselves as conservative, need for cognitive closure was positively and significantly related to preference for aggressive actions against the out-group. In the second study, the predicted interaction was investigated in the context of the terrorist threat in Poland. The findings indicated that high in need for closure conservatives showed greater hostility against Arabs and Muslims only when they believed that Poland was under threat of terrorist attacks inspired by Islamist fundamentalism
Heavy flavour production in DGLAP improved saturation model
The charm and beauty quark production in deep inelastic scattering at low
values of the Bjorken variable x is considered in the DGLAP improved saturation
model. After fitting parameters of the model to the structure function F_2, the
heavy quark contributions Fc_2 and Fb_2 are predicted. A good description of
the data is found. Predictions for the longitudinal structure function F_L and
the diffractive structure function FD_2 are also presented.Comment: 16 pages, 7 figures; typos corrected, references added, final
Phys.Rev. D versio
A global analysis of inclusive diffractive cross sections at HERA
We describe the most recent data on the diffractive structure functions from
the H1 and ZEUS Collaborations at HERA using four models. First, a Pomeron
Structure Function (PSF) model, in which the Pomeron is considered as an object
with parton distribution functions. Then, the Bartels Ellis Kowalski Wusthoff
(BEKW) approach is discussed, assuming the simplest perturbative description of
the Pomeron using a two-gluon ladder. A third approach, the Bialas Peschanski
(BP) model, based on the dipole formalism is then described. Finally, we
discuss the Golec-Biernat-W\"usthoff (GBW) saturation model which takes into
account saturation effects. The best description of all avaible measurements
can be achieved with either the PSF based model or the BEKW approach. In
particular, the BEKW prediction allows to include the highest
measurements, which are dominated by higher twists effects and provide an
efficient and compact parametrisation of the diffractive cross section. The two
other models also give a good description of cross section measurements at
small with a small number of parameters. The comparison of all predictions
allows us to identify interesting differences in the behaviour of the effective
pomeron intercept and in the shape of the longitudinal component of the
diffractive structure functions. In this last part, we present some features
that can be discriminated by new experimental measurements, completing the HERA
program.Comment: 32 pages, 18 figure
Nonlinear QCD Evolution: Saturation without Unitarization
We consider the perturbative description of saturation based on the nonlinear
QCD evolution equation of Balitsky and Kovchegov (BK). Although the nonlinear
corrections lead to saturation of the scattering amplitude locally in impact
parameter space, we show that they do not unitarize the total cross section.
The total cross section for the scattering of a strongly interacting probe on a
hadronic target is found to grow exponentially with rapidity. The origin of
this violation of unitarity is the presence of long range Coulomb fields away
from the saturation region. The growth of these fields with rapidity is not
tempered by the nonlinearity of the BK equation.Comment: 4 pages, RevTe
Non-linear evolution and high energy diffractive production
The ratio of the diffractive production to the total cross section in DIS is
computed as a function of the produced mass. The analysis is based on the
solution to the non-linear evolution equation for the diffraction dissociation
in DIS.
The obtained ratios almost do not depend on the central mass energy in
agreement with the HERA experimental data. This independence is argued to be a
consequence of the scaling phenomena displayed by the cross sections.
As a weakness point a significant discrepancy between the data and the
obtained results is found in the absolute values of the ratios. Several
explanatory reasons are discussed.Comment: 8 pages, 3 figure
Geometric Scaling in a Symmetric Saturation Model
We illustrate geometric scaling for the photon-proton cross section with a
very simple saturation model. We describe the proton structure function F2 at
small x in a wide kinematical range with an elementary functional form and a
small number of free parameters. We speculate that the symmetry between low and
high Q2 recently discovered in the data could be related to a well-known
symmetry of the two-gluon- exchange dipole-dipole cross section.Comment: 15 pages, 4 figure
QCD Saturation in the Semi-classical Approach
In this paper the semi-classical approach to the solution of non-linear
evolution equation is developed. We found the solution in the entire kinematic
region to the non-linear evolution equation that governs the dynamics in the
high parton density QCD. The large impact parameter () behavior of the
solution is discussed as well as the way how to include the non-perturbative
QCD corrections in this region of . The geometrical scaling behavior and
other properties of the solution in the saturation (Color Glass Condensate)
kinematic domain are analyzed. We obtain the asymptotic behavior for the
physical observables and found the unitarity bounds for them.Comment: 41 pp. 19 figures in eps file
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