67 research outputs found
Total and diffractive cross sections in enhanced Pomeron scheme
For the first time, a systematic analysis of the high energy behavior of
total and diffractive proton-proton cross sections is performed within the
Reggeon Field Theory framework, based on the resummation of all significant
contributions of enhanced Pomeron diagrams to all orders with respect to the
triple-Pomeron coupling. The importance of different classes of enhanced graphs
is investigated and it is demonstrated that absorptive corrections due to
"net"-like enhanced diagrams and due to Pomeron "loops" are both significant
and none of those classes can be neglected at high energies. A comparison with
other approaches based on partial resummations of enhanced diagrams is
performed. In particular, important differences are found concerning the
predicted high energy behavior of total and single high mass diffraction
proton-proton cross sections, with our values of at
TeV being some % higher and with the energy rise of
saturating well below the LHC energy. The main
causes for those differences are analyzed and explained
A New Approach to Nuclear Collisions at RHIC Energies
We present a new parton model approach for nuclear collisions at RHIC
energies (and beyond). It is a selfconsistent treatment, using the same
formalism for calculating cross sections like the total and the inelastic one
and, on the other hand, particle production. Actually, the latter one is based
on an expression for the total cross section, expanded in terms of cut Feynman
diagrams. Dominant diagrams are assumed to be composed of parton ladders
between any pair of nucleons, with ordered virtualities from both ends of the
ladder.Comment: 8 pages, 3 figures (proceedings Quark Matter 99
Enhanced Pomeron diagrams: re-summation of unitarity cuts
Unitarity cuts of enhanced Pomeron diagrams are analyzed in the framework of
the Reggeon Field Theory. Assuming the validity of the
Abramovskii-Gribov-Kancheli cutting rules, we derive a complete set of cut
non-loop enhanced graphs and observe important cancellations between certain
sub-classes of the latter. We demonstrate also how the present method can be
generalized to take into consideration Pomeron loop contributions
On the re-summation of enhanced Pomeron diagrams
Dominant contributions of enhanced Pomeron diagrams to elastic hadron-hadron
scattering amplitude are re-summed to all orders. The formalism is applied to
calculate total hadronic cross sections and elastic scattering slopes. An
agreement with earlier results is obtained
Higher twists in deep inelastic scattering
We perform an exploratory study of higher twist contributions to deep
inelastic scattering. We estimate the size of two major sources of higher
twist, namely absorptive corrections and the vector meson dominance (VMD)
contribution. We find that they give a sizeable higher twist component of F_2.
For example at x = 0.01 it is about 8% (17%) at Q^2 = 10 GeV^2 (4 GeV^2),
reaching up to 27% at x = 10^{-4} and Q^2 = 4 GeV^2. At the smaller x value the
largest contribution comes from absorptive corrections, while at the larger
values of x the VMD term dominates.Comment: The sign of the gluon rescattering twist-4 component has been
corrected and the manuscript modified accordingl
Double parton scatterings in high energy hadronic collisions
CDF has recently measured a large number of double parton scatterings. The
observed value of , the non perturbative parameter which
characterizes the process, is considerably smaller as compared with the naive
expectation. The small value of is likely to be an indication of
the importance of the two-body parton correlations in the many-body parton
distributions of the proton.Comment: 8 pages, latex file, no figures, contributions to the proceedings of
the ISMD9
How many of the scaling trends in collisions will be violated at sqrt{s_NN} = 14 TeV ? - Predictions from Monte Carlo quark-gluon string model
Multiplicity, rapidity and transverse momentum distributions of hadrons
produced both in inelastic and nondiffractive collisions at energies from
\,GeV to 14\,TeV are studied within the Monte Carlo quark-gluon
string model (QGSM). Good agreement with the available experimental data up to
\,TeV is obtained, and predictions are made for the collisions
at top LHC energy \,TeV. The model indicates that Feynman
scaling and extended longitudinal scaling remain valid in the fragmentation
regions, whereas strong violation of Feynman scaling is observed at
midrapidity. The Koba-Nielsen-Olesen (KNO) scaling in multiplicity
distributions is violated at LHC also. The origin of both maintenance and
violation of the scaling trends is traced to short range correlations of
particles in the strings and interplay between the multistring processes at
ultrarelativistic energies
Large multiplicity fluctuations and saturation effects in onium collisions
This paper studies two related questions in high energy onium-onium
scattering: the probability of producing an unusually large number of particles
in a collision, where it is found that the cross section for producing a
central multiplicity proportional to should decrease exponentially in
. Secondly, the nature of gluon (dipole) evolution when dipole
densities become so high that saturation effects due to dipole-dipole
interactions become important: measures of saturation are developed to help
understand when saturation becomes important, and further information is
obtained by exploiting changes of frame, which interchange unitarity and
saturation corrections.Comment: 30 pages LaTeX2e, 11 figures included using epsfig. Compressed
postscript of whole paper also available at
http://www.hep.phy.cam.ac.uk/theory/papers
Single and Double BFKL Pomeron Exchange and a Dipole Picture of High Energy Hard Processes
Onium-onium scattering at high energy is used to illustrate a dipole picture
of high energy hard scattering in the large limit. Single and double BFKL
pomeron exchanges are calculated in the leading logarithmic approximation. An
expression is given for the triple pomeron coupling when one of the pomeron's
momentum is zero while the other two have momentum transfer, t. This expression
is explicit and could be evaluated numerically. It has a
singularity at t=0.Comment: CU-TP-625, minor TeX problems of previous version have been fixe
Self-Consistency Requirement in High-Energy Nuclear Scattering
Practically all serious calculations of exclusive particle production in
ultra-relativistic nuclear or hadronic interactions are performed in the
framework of Gribov-Regge theory or the eikonalized parton model scheme.
It is the purpose of this paper to point out serious inconsistencies in the
above-mentioned approaches.
We will demonstrate that requiring theoretical self-consistency reduces the
freedom in modeling high energy nuclear scattering enormously.
We will introduce a fully self-consistent formulation of the
multiple-scattering scheme in the framework of a Gribov-Regge type effective
theory.
In addition, we develop new computational techniques which allow for the
first time a satisfactory solution of the problem in the sense that calculation
s of observable quantities can be done strictly within a self-consistent
formalism.Comment: 7 pages, 6 figure
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