2,872 research outputs found
Non-linear BFKL dynamics: color screening vs. gluon fusion
A feasible mechanism of unitarization of amplitudes of deep inelastic
scattering at small values of Bjorken is the gluon fusion. However, its
efficiency depends crucially on the vacuum color screening effect which
accompanies the multiplication and the diffusion of BFKL gluons from small to
large distances. From the fits to lattice data on field strength correlators
the propagation length of perturbative gluons is fermi. The
probability to find a perturbative gluon with short propagation length at large
distances is suppressed exponentially. It changes the pattern of (dif)fusion
dramatically. The magnitude of the fusion effect appears to be controlled by
the new dimensionless parameter , with the diffraction cone
slope standing for the characteristic size of the interaction region. It
should slowly decrease at large . Smallness of the
ratio makes the non-linear effects rather weak even at lowest
Bjorken available at HERA. We report the results of our studies of the
non-linear BFKL equation which has been generalized to incorporate the running
coupling and the screening radius as the infrared regulator.Comment: 16 pages, 2 figures, version accepted for publication, references
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Nonlinear kT factorization for Forward Dijets in DIS off Nuclei in the Saturation Regime
We develop the QCD description of the breakup of photons into forward dijets
in small-x deep inelastic scattering off nuclei in the saturation regime. Based
on the color dipole approach, we derive a multiple scattering expansion for
intranuclear distortions of the jet-jet transverse momentum spectrum. A special
attention is paid to the non-Abelian aspects of the propagation of color
dipoles in a nuclear medium. We report a nonlinear -factorization
formula for the breakup of photons into dijets in terms of the collective
Weizs\"acker-Williams (WW) glue of nuclei as defined in ref.
\cite{Saturation,NSSdijet}. For hard dijets with the transverse momenta above
the saturation scale the azimuthal decorrelation (acoplanarity) momentum is of
the order of the nuclear saturation momentum QA. For minijets with the
transverse momentum below the saturation scale the nonlinear kT-factorization
predicts a complete disappearance of the jet-jet correlation. We comment on a
possible relevance of the nuclear decorrelation of jets to the experimental
data from the STAR-RHIC Collaboration.Comment: 40 pages, 7 figure
Coulomb dissociation of a fast pion into two jets
We calculate the electromagnetic contribution to the scattering amplitude of
pion diffractive dissociation into di-jets which is described by one photon
exchange. The result shows that the factorization procedure known for the
description of exclusive reactions holds also for this quasi-exclusive process.
We find that the longitudinal momentum distribution of di-jets does not depend
on the form of the pion distribution amplitude. We discuss the magnitude of the
cross section.Comment: 7 pages, 3 .eps figures, Late
The triple-pomeron regime and the structure function of the pomeron in the diffractive deep inelastic scattering at very small x
Misprints and numerical coefficients corrected, a bit of phenomenology and
one figure added. The case for the linear evolution of the unitarized structure
functions made stronger.Comment: KFA-IKP(Th)-1993-17, Landau-16/93, 46 pages, 14 figures upon request
from N.Nikolaev, [email protected]
Anatomy of the differential gluon structure function of the proton from the experimental data on F_2p
The use of the differential gluon structure function of the proton introduced by Fadin, Kuraev and Lipatov in 1975 is called upon in
many applications of small-x QCD. We report here the first determination of
from the experimental data on the small-x proton structure
function . We give convenient parameterizations for based partly on the available DGLAP evolution fits (GRV, CTEQ &
MRS) to parton distribution functions and on realistic extrapolations into soft
region. We discuss an impact of soft gluons on various observables. The
x-dependence of the so-determined varies strongly with Q^2
and does not exhibit simple Regge properties. None the less the hard-to-soft
diffusion is found to give rise to a viable approximation of the proton
structure function F_{2p}(x,Q^2) by the soft and hard Regge components with
intercepts \Delta_{soft}=0 and \Delta_{hard}\sim 0.4.Comment: 37 pages, 25 figure
Spin-dependent pbar-d cross sections at low and intermediate energies
Antiproton-deuteron () scattering is calculated at beam energies
below 300 MeV within the Glauber approach, utilizing the amplitudes of the
J\"ulich models. A good agreement is obtained with available
experimental data on upolarized differential and integrated cross
sections. Predictions for polarized total cross sections are
presented, obtained within the single scattering approximation including
Coulomb-nuclear interference effects. It is found that the total longitudinal
and transversal cross sections are comparable in absolute value to
those for scattering.
The kinetics of polarization buildup is considered.Comment: 8 pages, 5 figures, to appear in proceedings of the 19th
international Spin Physics Symposium, September 27 - October 2, 2010,
Juelich, German
Ultrahigh energy neutrinos and non-linear QCD dynamics
The ultrahigh energy neutrino-nucleon cross sections are computed taking into
account different phenomenological implementations of the non-linear QCD
dynamic s. Based on the color dipole framework, the results for the saturation
model supplemented by DGLAP evolution as well as for the BFKL formalism in the
geometric scaling regime are presented. They are contrasted with recent
calculations using NLO DGLAP and unified BFKL-DGLAP formalisms.Comment: 5 pages, 2 figures. Version to be published in Physical Review
Exclusive photoproduction of hard dijets and magnetic susceptibility of QCD vacuum
We argue that coherent production of hard dijets by linearly polarized real
photons can provide direct evidence for chirality violation in hard processes,
the first measurement of the magnetic susceptibility of the quark condensate
and the photon distribution amplitude. It can also serve as a sensitive probe
of the generalized gluon parton distribution. Numerical calculations are
presented for HERA kinematics.Comment: 4 pages, 4 figure
Vector meson electroproduction at next-to-leading order
The process of a light neutral vector meson electroproduction is studied in
the framework of QCD factorization in which the amplitude factorizes in a
convolution of the nonperturbative meson distribution amplitude and the
generalized parton densities with the perturbatively calculable hard-scattering
amplitudes. We derive a complete set of hard-scattering amplitudes at
next-to-leading order for the production of vector mesons, .Comment: latex, 6 pages, with corrected Eq. (12) and added remark on
dimensional regularisatio
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