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 $\sigma_{pp}^{{\rm tot}}$ at $\sqrt{s}=14$ TeV being some $25\div40$% higher and with the energy rise of $\sigma_{{\rm HM}}^{{\rm SD}}$ 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 $\sigma_{eff}$, the non perturbative parameter which characterizes the process, is considerably smaller as compared with the naive expectation. The small value of $\sigma_{eff}$ 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 pppp 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 $pp$ collisions at energies from $\sqrt{s} = 200$\,GeV to 14\,TeV are studied within the Monte Carlo quark-gluon string model (QGSM). Good agreement with the available experimental data up to $\sqrt{s} = 13$\,TeV is obtained, and predictions are made for the collisions at top LHC energy $\sqrt{s} = 14$\,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 $k$ should decrease exponentially in $\sqrt{k}$. 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 $N_c$ 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 $(-t)^{-{1\over 2}}$ 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