588 research outputs found
EFFECTS OF SHADOWING IN DOUBLE POMERON EXCHANGE PROCESSES
The effects of shadowing in double Pomeron exchange processes are
investigated within an eikonal approach with a Gaussian input. Damping factors
due to screening are calculated for this process and compared with the factors
obtained for total, elastic and single diffraction cross sections. Our main
conclusion is that counting rate calculations, of various double Pomeron
exchange processes (without screening corrections) such as heavy quark and
Higgs production are reduced by a factor of 5 in the LHC energy range, when
screening corrections are applied.Comment: 9 pages, latex, 5 figures obtainable from author
Evidence for xi- and t-dependent damping of the Pomeron Flux in the proton
We show that a triple-Regge parametrization of inclusive single diffraction
agrees with the data in the following two domains: (a) xi > 0.03 at all t, (b)
|t| > 1 GeV^2 at all xi. Since the triple-Regge parametrization fails when
applied to the full xi-t range of the total single-diffractive cross section,
we conclude that damping occurs only at low-xi and low-|t|. We give a (``toy'')
parametrization of the damping factor, D(xi), valid at low-|t|, which describes
the diffractive differential cross-section (dsig/dt) data at the ISR and
roughly accounts for the observed s-dependence of diffractive total
cross-section up to Tevatron energies. However, an effective damping factor
calculated for the CDF fitted function for dsig/dxidt at sqrt(s} = 1800 GeV and
|t| = 0.05 GeV^2, suggests that, at fixed-xi, damping increases as s increases.
We conjecture that, in the regions where the triple-Regge formalism describes
the data and there is no evidence of damping, factorization is valid and the
Pomeron-flux-factor may be universal. With the assumption that the observed
damping is due to multi-Pomeron exchange, our results imply that the recent UA8
demonstration that the effective Pomeron trajectory flattens for |t| > 1 GeV$^2
is evidence for the onset of the perturbative 2-gluon pomeron. Our damping
results may also shed some light on the self-consistency of recent measurements
of hard-diffractive jet production cross sections in the UA8, CDF and ZEUS
experiments.Comment: 19 pages, 7 Encapsulated Postscript figures, LaTex, Phys. Lett. B (in
press - 1998
Systematic Regge theory analysis of omega photoproduction
Systematic analysis of available data for -meson photoproduction is
given in frame of Regge theory. At photon energies above 20 GeV the
reaction is entirely dominated by Pomeron exchange.
However, it was found that Pomeron exchange model can not reproduce the
and data at high energies
simultaneously with the same set of parameters. The comparison between
and data indicates a large room for meson exchange contribution to
-meson photoproduction at low energies. It was found that at low
energies the dominant contribution comes from and -meson exchanges.
There is smooth transition between the meson exchange model at low energies and
Regge theory at high energies.Comment: 7 pages, 8 figures, revtex
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
Behaviour of the forward peak in hard diffractive leptoproduction of vector mesons
The measured forward slope in elastic and inelastic leptoproduction of vector
mesons differ by a substantial amount. In an attempt to describe this
phenomenon we construct a two radii model for the target proton, and estimate
the effective parameters of the hard Pomeron obtained from a pQCD dipole model
with eikonal shadowing corrections (SC). We show that the SC reduce the
intercept of the hard Pomeron and generate an effective shrinkage of the
forward peak and a diffractive dip at , which appears to
affect the value of the experimentally measured slope.Comment: 18 pages, 7 figures, one table, everything in tar.gz fil
The Role of Screening Corrections in High Energy Photoproduction
The role of screening corrections, calculated using the eikonal model, is
discussed in the context of soft photoproduction. We present a comprehensive
calculation considering the total,elastic and diffractive cross sections
jointly. We examine the differences between our results and those obtained from
the supercritical Pomeron-Reggeon model with no unitarity corrections.Comment: 12 pages (Replacement due to PostScript file problem in previous
posting
The Dipole Picture and Saturation in Soft Processes
We attempt to describe soft hadron interactions in the framework of
saturation models, one based upon the Balitsky-Kovchegov non-linear equation
and another one due to Golec-Biernat and W\"{u}sthoff. For , , and scattering the relevant hadronic wave functions are formulated, and total,
elastic cross-sections, and the forward elastic slope are calculated and
compared to experimental data. The saturation mechanism leads to reasonable
reproduction of the data for the quantities analyzed, except for the forward
elastic slope, where the predicted increase with energy is too moderate.Comment: 12 pages, 4 figures. One figure and several explanations are added.
The version is to appear in PL
Observing the Odderon: Tensor Meson Photoproduction
We calculate high-energy photoproduction of the tensor meson by
odderon and photon exchange in the reaction , where X is either the nucleon or the sum of the N(1520) and N(1535)
baryon resonances. Odderon exchange dominates except at very small transverse
momentum, and we find a cross section of about 20 nb at a centre-of-mass energy
of 20 GeV. This result is compared with what is currently known experimentally
about photoproduction. We conclude that odderon exchange is not ruled out
by present data. On the contrary, an odderon-induced cross section of the above
magnitude may help to explain a puzzling result observed by the E687
experiment.Comment: 19 pages, 11 figure
Photon-Photon and Pomeron-Pomeron Processes in Peripheral Heavy Ion Collisions
We estimate the cross sections for the production of resonances, pion pairs
and a central cluster of hadrons in peripheral heavy-ion collisions through
two-photon and double-pomeron exchange, at energies that will be available at
RHIC and LHC. The effect of the impact parameter in the diffractive reactions
is introduced, and imposing the condition for realistic peripheral collisions
we verify that in the case of very heavy ions the pomeron-pomeron contribution
is indeed smaller than the electromagnetic one. However, they give a
non-negligible background in the collision of light ions. This diffractive
background will be more important at RHIC than at LHC.Comment: 22 pages, 1 Postscript figures, 4 tables, to appear in Phys. Rev.
Direct extraction of hadronic form factors from elastic-scattering data
Non-forward elastic hadron-scattering data are collected and analysed within
the Regge approach. Through an analysis of the data in small bins in , we
have directly extracted the pomeron trajectory and the hadronic form factors
(or reggeon couplings). We found higher values than usually used for the
intercept and for the slope of the soft pomeron trajectory. The presence of
zeros in for the effective hadronic form factors is emphasised.Comment: 4 pages, 5 figures, talk given at Diffraction 2004, Cala Gonone,
Sardinia, Italy, 18-23 September 200
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