1,273 research outputs found
Transverse target spin asymmetry in inclusive DIS with two-photon exchange
We study the transverse target spin dependence of the cross section for
inclusive electron-nucleon scattering with unpolarized beam. Such dependence is
absent in the one-photon exchange approximation (Christ-Lee theorem) and arises
only in higher orders of the QED expansion, from the interference of one-photon
and absorptive two-photon exchange amplitudes as well as from real photon
emission (bremsstrahlung). We demonstrate that the transverse spin-dependent
two-photon exchange cross section is free of QED infrared and collinear
divergences. We argue that in DIS kinematics the transverse spin dependence
should be governed by a "parton-like" mechanism in which the two-photon
exchange couples mainly to a single quark. We calculate the normal spin
asymmetry in an approximation where the dominant contribution arises from quark
helicity flip due to interactions with non-perturbative vacuum fields
(constituent quark picture) and is proportional to the quark transversity
distribution in the nucleon. Such helicity-flip processes are not significantly
Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark
subprocess is of the order of the chiral symmetry breaking scale, mu_chiral^2
>> Lambda_QCD^2. We estimate the asymmetry in the kinematics of the planned
Jefferson Lab Hall A experiment to be of the order 10^{-4}, with different sign
for proton and neutron. We also comment on the spin dependence in the limit of
soft high-energy scattering.Comment: 22 pages, 14 figures; uses revtex
Two-scale hadronic structure and elastic pp scattering: predicted and measured
We update the comparison with experiment of the dynamical model of
high-energy hadron interactions based on the two scale structure of hadrons.
All predictions made over decade ago are confirmed with a high precision by the
TOTEM experiment at LHC.Comment: 6 pages, 6 figure
A unitarized model of inclusive and diffractive DIS with Q2-evolution
We discuss the interplay of low-x physics and QCD scaling violations by
extending the unified approach describing inclusive structure functions and
diffractive production in interactions proposed in previous papers,
to large values of Q2. We describe the procedure of extracting, from the
non-perturbative model, initial conditions for the QCD evolution that respect
unitarity. Assuming Regge factorization of the diffractive structure function,
a similar procedure is proposed for the calculation of hard diffraction. The
results are in good agreement with experimental data on the proton structure
function and the most recent data on the reduced diffractive cross
section, x_P \sigma_r^{\D(3)}. Predictions for both and are
presented in a wide kinematical range and compared to calculations within
high-energy QCD.Comment: 22 pages, 12 figure
On the shape of a rapid hadron in QCD
We visualize the fundamental property of pQCD: the smaller size of the
colorless quark-gluon configurations leads to a more rapid increase of its
interaction with energy. Within the frame of dipole model we use the
factorization theorem to generalize the DGLAP approximation and/or leading
approximation and evaluate the interaction of quark dipole with a
target. In the limit of fixed and we found the increase with
energy of transverse momenta of quark(antiquark) within q pair produced
by strongly virtual photon. The average is evaluated analytically
within the double logarithmic approximation. We demonstrate that the invariant
mass of the q pair increases with the energy as
, where for transverse
photons, and as
for longitudinal photons, where at the energies of the
order GeV (). The magnitude of the effect
depends strongly on the small behavior of the gluon distribution. Similar
pattern of the energy dependence of is found in the LO DGLAP
approximation generalized to account for factorization. We discuss the
impact of the found phenomenon on the dependence of the coherence length on the
initial energy and demonstrate that the shape of final hadron state in DIS has
biconcave form instead of pancake. Some implications of the found phenomena for
the hard processes in pp collisions are discussed.Comment: 14 pages, 2 figures, uses epstopdf.sty typos correcte
Higher twist jet broadening and classical propagation
The transverse broadening of jets produced in deep-inelastic scattering (DIS)
off a large nucleus is studied in the collinear limit. A class of medium
enhanced higher twist corrections are re-summed to calculate the transverse
momentum distribution of the produced collinear jet. In contrast to previous
approaches, resummation of the leading length enhanced higher twist corrections
is shown to lead to a two dimensional diffusion equation for the transverse
momentum of the propagating jet. Results for the average transverse momentum
obtained from this approach are then compared to the broadening expected from a
classical Langevin analysis for the propagation of the jet under the action of
the fluctuating color Lorentz force inside the nucleons. The set of
approximations that lead to identical results from the two approaches are
outlined. The relationship between the momentum diffusion constant and the
transport coefficient is explicitly derived.Comment: 17 pages, 6 figures, revtex4, references added, typos corrected,
discussion update
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
Eigenmodes of Decay and Discrete Fragmentation Processes
Linear rate equations are used to describe the cascading decay of an initial
heavy cluster into fragments. This representation is based upon a triangular
matrix of transition rates. We expand the state vector of mass multiplicities,
which describes the process, into the biorthonormal basis of eigenmodes
provided by the triangular matrix. When the transition rates have a scaling
property in terms of mass ratios at binary fragmentation vertices, we obtain
solvable models with explicit mathematical properties for the eigenmodes. A
suitable continuous limit provides an interpolation between the solvable
models. It gives a general relationship between the decay products and the
elementary transition rates.Comment: 6 pages, plain TEX, 2 figures available from the author
Hard collinear gluon radiation and multiple scattering in a medium
The energy loss of hard jets produced in the Deep-Inelastic scattering (DIS)
off a large nucleus is considered in the collinear limit. In particular, the
single gluon emission cross section due to multiple scattering in the medium is
calculated. Calculations are carried out in the higher-twist scheme, which is
extended to include contributions from multiple transverse scatterings on both
the produced quark and the radiated gluon. The leading length enhanced parts of
these power suppressed contributions are resummed. Various interferences
between such diagrams lead to the Landau-Pomeranchuk-Migdal (LPM) effect. We
resum the corrections from an arbitrary number of scatterings and isolate the
leading contributions which are suppressed by one extra power of the hard scale
. All powers of the emitted gluon forward momentum fraction are
retained. We compare our results with the previous calculation of single
scattering per emission in the higher-twist scheme as well as with multiple
scattering resummations in other schemes. It is found that the leading
() contribution to the double differential gluon production cross
section, in this approach, is equivalent to that obtained from the single
scattering calculation once the transverse momentum of the final quark is
integrated out. We comment on the generalization of this formalism to
Monte-Carlo routines.Comment: 30 pages, 7 figures, revtex4, typos correcte
Large distance behaviour of light cone operator product in perturbative and nonperturbative QCD regimes
We evaluate the coordinate space dependence of the matrix elements of the
commutator of the electromagnetic and gluon currents in the vicinity of the
light-cone but at large distances within the parton model, DGLAP, the
resummation approaches to the small x behaviour of DIS processes, and for the
Unitarity Bound. We find that an increase of the commutator with relative
distance as is the generic property of QCD
at small but fixed space-time interval in perturbative and
nonperturbative QCD regimes. We explain that the factor follows within the
dipole model (QCD factorization theorem) from the properties of Lorents
transformation. The increase of disappeares at central impact parameters
if cross section of DIS may achieve the Unitarity Limit. We argue that such
long range forces are hardly consistent with thermodynamic equilibrium while a
Unitarity Limit may signal equilibration. Possible implications of this new
long range interaction are briefly discussed.Comment: 23 page
Number of Collisions in the Glauber Model and Beyond
The so called number of hadron-nucleus collisions n_coll(b) at impact
parameter b, and its integral value N_coll, which are used to normalize the
measured fractional cross section of a hard process, are calculated within the
Glauber-Gribov theory including the effects of nucleon short-range
correlations. The Gribov inelastic shadowing corrections are summed to all
orders by employing the dipole representation. Numerical calculations are
performed at the energies of the BNL Relativistic Heavy Ion Collider (RHIC) and
CERN Large Hadron Collider (LHC). We found that whereas the Gribov corrections
generally increase the value of N_coll, the inclusion of nucleon correlations,
acting in the opposite directions, decreases it by a comparable amount. The
interplay of the two effects varies with the value of the impact parameter.Comment: Text expanded; typos corrected; results and conclusions unchanged. To
appear in Phys. Rev.
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