1,497 research outputs found
Nuclear shadowing in inclusive and tagged deuteron structure functions and extraction of F_2^p-F_2^n at small x from electron-deuteron collider data
We review predictions of the theory of leading twist nuclear shadowing for
inclusive unpolarized and polarized deuteron structure functions F_2^D, g_1^D
and b_1^D and for the tagged deuteron structure function F_2^D(x,Q^2,\vec{p}).
We analyze the possibility to extract the neutron structure function F_2^n from
electron-deuteron data and demonstrate that an account of leading twist nuclear
shadowing leads to large corrections for the extraction of F_2^n from the
future deuteron collider data both in the inclusive and in the tagged structure
function modes. We suggest several strategies to address the extraction of
F_2^n and to measure at the same time the effect of nuclear shadowing via the
measurement of the distortion of the proton spectator spectrum in the
semi-inclusive e D \to e^{\prime}NX process. We address the issue of the final
state interactions in the e D \to e^{\prime}NX process and examine how they
affect the extraction of F_2^n.Comment: 19 pages, 7 figures. Published in Mod. Phys. Lett.
Resolving the J/\psi RHIC puzzles at LHC
Experiments with gold-gold collisions at RHIC have revealed (i) stronger
suppression of charmonium production at forward rapidity than at midrapidity
and (ii) the similarity between the suppression degrees at RHIC and SPS
energies. To describe these findings we employ the model that includes nuclear
shadowing effects, calculated within the Glauber-Gribov theory,
rapidity-dependent absorptive mechanism, caused by energy-momentum
conservation, and dissociation and recombination of the charmonium due to
interaction with co-moving matter. The free parameters of the model are tuned
and fixed by comparison with experimental data at lower energies. A good
agreement with the RHIC results concerning the rapidity and centrality
distributions is obtained for both heavy Au+Au and light Cu+Cu colliding
system. For pA and A+A collisions at LHC the model predicts stronger
suppression of the charmonium and bottomonium yields in stark contrast to
thermal model predictions.Comment: SQM2008 proceedings, 6 page
Asymptotic behavior of double parton distribution functions
The double parton distribution functions are investigated in the region of
small longitudinal momentum fractions in the leading logarithm approximation of
perturbative QCD. It is shown that these functions have the factorization
property in the case of one slow and one fast parton.Comment: 7 pages, revtex
Probing coherent charmonium photoproduction off light nuclei at medium energies
We demonstrate how the elementary amplitudes , the
amplitude of the nondiagonal transition, and
the total and cross sections can be determined from
measurements of the coherent and photoproduction off light
nuclei at moderate energies. For this purpose we provide a detailed numerical
analysis of the coherent charmonium photoproduction off silicon within the
generalized vector dominance model (GVDM) adjusted to account for the physics
of charmonium models and color transparency phenomenon.Comment: 8 pages, 5 figures (color
Double parton scattering in double logarithm approximation of perturbative QCD
Using the explicit form of the known single distribution functions (the
Green's functions) in the double logarithm approximation of perturbative QCD,
we analyze the structure of splitting diagrams as a source of double parton
perturbative correlations in the proton. The related phenomenological effects
are discussed for the conditions of the LHC experiments.Comment: 8 pages, 1 figure, Refs. and explanations added, published version
(Phys. Rev. D
The casuality and/or energy-momentum conservation constraints on QCD amplitudes in small x regime
The causality and/or the energy-momentum constraints on the amplitudes of
high energy processes are generalized to QCD. The constraints imply that the
energetic parton may experience at most one inelastic collision only and that
the number of the constituents in the light cone wave function of the
projectile is increasing with the collision energy and the atomic number.Comment: 24 pages,8 figures. The paper is streamlined, some references are
changed and misprints are eliminate
On the behaviour of single scale hard small processes in QCD near the black disc limit
We argue that at sufficiently small Bjorken where pQCD amplitude rapidly
increases with energy and violates probability conservation the shadowing
effects in the single-scale small hard QCD processes can be described by an
effective quantum field theory of interacting quasiparticles. The
quasiparticles are the perturbative QCD ladders. We find, within the WKB
approximation, that the smallness of the QCD coupling constant ensures the
hierarchy among many-quasiparticle interactions evaluated within physical
vacuum and in particular, the dominance in the Lagrangian of the triple
quasiparticle interaction. It is explained that the effective field theory
considered near the perturbative QCD vacuum contains a tachyon relevant for the
divergency of the perturbative QCD series at sufficiently small . We solve
the equations of motion of the effective field theory within the WKB
approximation and find the physical vacuum and the transitions between the
false (perturbative) and physical vacua. Classical solutions which dominate
transitions between the false and physical vacua are kinks that cannot be
decomposed into perturbative series over the powers of . These kinks
lead to color inflation and the Bose-Einstein condensation of quasiparticles.
The account of the quantum fluctuations around the WKB solution reveals the
appearance of the "massless" particles-- "phonons". It is explained that
"phonons" are relevant for the black disc behaviour of small processes,
leading to a Froissart rise of the cross-section. The condensation of the
ladders produces a color network occupying a "macroscopic" longitudinal volume.
We discuss briefly the possible detection of new QCD effects.Comment: 24 pages, 1 Figure. References added, and several misprints
eliminate
A fresh look at double parton scattering
A revised formula for the inclusive cross section for double parton
scattering in terms of the modified collinear two-parton distributions
extracted from deep inelastic scattering is suggested. The possible
phenomenological issues are discussed.Comment: 6 pages, 2 figures, revtex4, discussion slightly modified, 3
references adde
Gluon-gluon contributions to the production of continuum diphoton pairs at hadron colliders
We compute the contributions to continuum photon pair production at hadron
colliders from processes initiated by gluon-gluon and gluon-quark scattering
into two photons through a four-leg virtual quark loop. Complete two-loop cross
sections in perturbative quantum chromodynamics are combined with contributions
from soft parton radiation resummed to all orders in the strong coupling
strength. The structure of the resummed cross section is examined in detail,
including a new type of unintegrated parton distribution function affecting
azimuthal angle distributions of photons in the pair's rest frame. As a result
of this analysis, we predict diphoton transverse momentum distributions in
gluon-gluon scattering in wide ranges of kinematic parameters at the Fermilab
Tevatron collider and the CERN Large Hadron Collider.Comment: 28 pages, 11 figures; published versio
Anomalous Dimensions of High Twist Operators in QCD at and large $Q^2
The anomalous dimensions of high-twist operators in deeply inelastic
scattering () are calculated in the limit when the moment variable
(or ) and at large (the double
logarithmic approximation) in perturbative QCD. We find that the value of
in this approximation behaves as where . This
implies that the contributions of the high-twist operators give rise to an
earlier onset of shadowing than was estimated before. The derivation makes use
of a Pomeron exchange approximation, with the Pomerons interacting
attractively. We find that they behave as a system of fermions.Comment: jytex (see macros directory), 18 pages , 9 figures, uuencoded at back
of file, FERMILAB-PUB-93/243-
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