3,103 research outputs found
kt-factorization for Hard Processes in Nuclei
Two widely proposed kt-dependent gluon distributions in the small-x
saturation regime are investigated using two particle back-to-back correlations
in high energy scattering processes. The Weizsacker-Williams gluon
distribution, interpreted as the number density of gluon inside the nucleus, is
studied in the quark-antiquark jet correlation in deep inelastic scattering. On
the other hand, the unintegrated gluon distribution, defined as the Fourier
transform of the color-dipole cross section, is probed in the direct photon-jet
correlation in pA collisions. Dijet-correlation in pA collisions depends on
both gluon distributions through combination and convolution in the large Nc
limit.Comment: 8 pages, 1 figur
Universality of multi-particle production in QCD at high energies
By studying the color structure of multi-particle production processes in
p+A-type (dilute-dense) collisions, we find that higher-point functions beyond
typical dipoles and quadrupoles, e.g., sextupoles, octupoles, etc., naturally
appear in the cross sections, but are explicitly suppressed in the large-N_c
limit. We evaluate the sextupole in the McLerran-Venugopalan model and find
that, in general, its analytical form cannot be written as combination of
dipoles and quadrupoles. Within the Color Glass Condensate framework, we
present a proof that in the large-N_c limit, all multi-particle production
processes in the collision of a dilute system off a dense can, up to all orders
in \alpha_s, be described in terms of only dipoles and quadrupoles.Comment: 24 pages, 16 figures, Published in Phys.Rev.
Medium-induced gluon branching
We study the evolution of an energetic jet which radiates gluons while
propagating through a dense QCD medium modeled as a random distribution of
color sources. Motivated by the heavy ion experimental program at the LHC, we
focus on the medium-induced radiation of (relatively) soft gluons, which are
abundantly emitted at large angles and thus can transport a small fraction of
the jet energy far away from the jet axis. We perform a complete calculation of
the medium-induced gluon branching in the regime where the gluons that take
part in the branching undergo multiple soft scattering with the medium. We
extend the BDMPSZ theory of radiative energy loss by including the transverse
momentum dependence in the kernel that describes the branching and by analyzing
the correlations between the two offspring gluons. We demonstrate that these
gluons lose color coherence with respect to each other over a time scale that
is comparable to the duration of the branching. It follows that interference
effects between successive emissions are suppressed, a necessary ingredient for
a description of multiple emission of soft gluons by a probabilistic, branching
process.Comment: 51 pages, 14 figure
On the linearly polarized gluon distributions in the color dipole model
We show that the linearly polarized gluon distributions appear in the color
dipole model as we derive the full cross sections of the DIS dijet production
and the Drell-Yan dijet ( jet correlation) process. Together with the
normal Weizs\"acker-Williams gluon distribution, the linearly polarized one
will contribute to the DIS dijet production cross section as the coefficient of
the term in the correlation limit. We also derive the
exact results for the cross section of the Drell-Yan dijet process, and find
that the linearly polarized dipole gluon distribution which is identical to the
normal dipole gluon distribution involves in the cross section. The results
obtained in this paper agree with the previous transverse momentum dependent
factorization study. We further derive the small- evolution of these
linearly polarized gluon distributions and find that they rise as gets
small at high energy.Comment: 10 pages,v2 with minor revisio
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Unintegrated Gluon Distributions at Small-x
The study of strong interactions at very high energies has prompted a large interest in the small-x regime of quantum chromodynamics where partons carry a small fraction of the momentum of their parent hadrons. In this regime gluon occupation numbers are believed to be very high leading to saturation of the corresponding parton densities. This thesis is intended to explore the validity of factorization approaches in the small-x regime and establish a relation with partonic interpretations when possible. Two fundamental unintegrated (transverse momentum dependent) gluon distributions are proposed as fundamental building blocks to describe all processes sensitive to the small-x regime which admit a factorized description. Single-particle production processes and two-particle production processes are studied in asymmetric collisions of a dilute probe scattering from a dense target and it is shown that it is possible to recover factorized expression in a particular kinematical limit
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