588 research outputs found
Gamma(*)Gamma(*) reaction at high energies
The energy available for gamma(*)gamma(*) physics at LEP2 is opening a new
window on the study of diffractive phenomena, both non-perturbative and
perturbative. We discuss some of the uncertainties and problems connected with
the experimental measurements and their interpretation.Comment: 6 pages, 6 figures, submitted to proceedings of the Durham Collider
Workshop, 22-26 September 199
Double Asymptotic Scaling '96
We review recent HERA data on the structure function F_2 at small x and large
Q^2. We show that the salient features of the data are revealed by comparing
them to the double asymptotic scaling behaviour which F_2 is predicted to
satisfy in perturbative QCD.Comment: 5 pages, LaTeX with espcrc2.sty (included), 11 figures included by
epsfi
The total virtual photoabsorption cross section, deeply virtual Compton scattering and vector-meson production
Based on the two-gluon-exchange dynamical mechanism for deeply inelastic
scattering at low x ~= Q^2/W^2 <<1, we stress the intimate connection between
the total virtual photoabsorption cross section, deeply virtual Compton
scattering and vector-meson electroproduction. A simple expression for the
cross section for deeply virtual Compton scattering is derived. Parameter-free
predictions are obtained for deeply-virtual Compton forward scattering and
vector-meson forward production, once the parameters in the total virtual
photoabsorption cross section are determined in a fit to the experimental data
on deeply inelastic scattering. Our predictions are compared with the
experimental data from HERA.Comment: 31 pages Latex, 10 figures and 1 tabl
Impact of saturation on spin effects in proton-proton scattering
For pomerons described by a sum of two simple-pole terms, a soft and a hard
pomeron, the unitarity bounds from saturation in impact-parameter space are
examined. We consider the effect of these bounds on observables linked with
polarisation, such as the analyzing power in elastic proton-proton scattering,
for LHC energies. We obtain the s and t dependence of the Coulomb-nuclear
interference at small momentum transfer, and show that the effect of the hard
pomeron may be observed at the LHC.Comment: 8 pages, 2 figures, presented by O.V.S. at the Advanced Studies
Institute "Symetries and Spin" (SPIN-Praha-2004), Prague, July 5 - July 10,
200
Final State Interaction Phases in Decay Amplitudes
A simple Regge pole model for scattering explains the large between isospin amplitudes which is observed at the D meson mass
(). It predicts
at the B mass. Implications for () decays and extensions of the
model to other two-body decay channels are briefly discussed.Comment: 8pages,late
Spin constraints on Regge predictions and perturbative evolution in high energy collisions
Two key issues in the application of perturbative QCD and Regge predictions
to high energy processes are whether the hard and soft pomerons should be
considered as two separate distinct exchanges and whether the Regge intercepts
are Q^2 independent or not. Models involving a distinct hard pomeron exchange
predict much larger values for the LHC total cross-section. Here we argue that
there is a polarized analogue of this issue in the isovector part of the spin
structure function g_1 and that the spin data appear to favour a distinct hard
exchange.Comment: 8 page
Q^2 dependence of diffractive vector meson electroproduction
We give a general formula for the cross section for diffractive vector meson
electroproduction, gamma^* p -> Vp. We first calculate diffractive qqbar
production, and then use parton-hadron duality by projecting out the J^P = 1^-
state in the appropriate mass interval. We compare the Q^2 dependence of the
cross section for the diffractive production of rho and J/psi mesons with
recent HERA data. We include the characteristic Q^2 dependence associated with
the use of the skewed gluon distribution. We give predictions for
sigma_L/sigma_T for both rho and J/psi production.Comment: 15 pages, LaTeX, including five PostScript figure
An upper bound on the total inelastic cross-section as a function of the total cross-section
Recently Andr\'e Martin has proved a rigorous upper bound on the inelastic
cross-section at high energy which is one-fourth of the known
Froissart-Martin-Lukaszuk upper bound on . Here we obtain an
upper bound on in terms of and show that the
Martin bound on is improved significantly with this added
information.Comment: 4 page
Coulomb Corrections for Coherent Electroproduction of Vector Mesons: Eikonal Approximation
Virtual radiative corrections due to the long range Coulomb forces of heavy
nuclei with charge Z may lead to sizeable corrections to the Born cross section
usually used for lepton-nucleus scattering processes. An introduction and
presentation of the most important issues of the eikonal approximation is
given. We present calculations for forward electroproduction production of rho
mesons in a framework suggested by the VDM (vector dominance model), using the
eikonal approximation. It turns out that Coulomb corrections may become
relatively large. Some minor errors in the literature are corrected.Comment: 14 pages, 6 figures, published versio
Regge phenomenology of pion photoproduction off the nucleon at forward angles
We present a Regge model for pion photoproduction which is basically free of
parameters within the framework of the s-channel helicity amplitude. We use
coupling constants of all exchanged mesons determined from empirical decay
widths or from the SU(3) relations together with consistency check with
existing estimates that are widely accepted in other reaction processes. Cross
sections and spin polarization asymmetries at various photon energies are
analyzed and results are obtained in better agreement with experimental data
without referring to any fitting procedure.Comment: 19 pages, 20 figures, two column, revtex
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