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

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

Monte Carlo treatment of hadronic interactions in enhanced Pomeron scheme: I. QGSJET-II model

The construction of a Monte Carlo generator for high energy hadronic and nuclear collisions is discussed in detail. Interactions are treated in the framework of the Reggeon Field Theory, taking into consideration enhanced Pomeron diagrams which are resummed to all orders in the triple-Pomeron coupling. Soft and "semihard" contributions to the underlying parton dynamics are accounted for within the "semihard Pomeron" approach. The structure of cut enhanced diagrams is analyzed; they are regrouped into a number of subclasses characterized by positively defined contributions which define partial weights for various "macro-configurations" of hadronic final states. An iterative procedure for a Monte Carlo generation of the structure of final states is described. The model results for hadronic cross sections and for particle production are compared to experimental data

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

Anisotropic flow of charged and identified hadrons in the quark-gluon string model for Au+Au collisions at sqrt(s) = 200 GeV

The pseudorapidity behaviour of the azimuthal anisotropy parameters v_1 and v_2 of inclusive charged hadrons and their dependence on the centrality has been studied in Au+Au collisions at full RHIC energy of sqrt(s) = 200 GeV within the microscopic quark-gluon string model. The QGSM simulation results for the directed flow v_1 show antiflow alignment within the pseudorapidity range |eta| < 2 in a fair agreement with the experimental v_1(eta) data, but cannot reproduce the further development of the antiflow up to |eta| around 3.5. The eta dependence of the elliptic flow v_2 extracted from the simulations agrees well with the experimental data in the whole pseudorapidity range for different centrality classes. The centrality dependence of the integrated elliptic flow of charged hadrons in the QGSM almost coincides with the PHOBOS experimental distribution. The transverse momentum dependence of the elliptic flow of identified and inclusive charged hadrons is studied also. The model reproduces quantitatively the low p_T part of the distributions rather good, but underestimates the measured elliptic flow for transverse momenta p_T > 1 GeV/c. Qualitatively, however, the model is able to reproduce the saturation of the v_2(p_T) spectra with rising p_T as well as the crossing of the elliptic flow for mesons and baryons.Comment: REVTeX, 10 pages, 10 figures, v2: extended discussion of the model results, accepted for publication in Phys. Rev.

Initial Condition for QGP Evolution from NEXUS

We recently proposed a new approach to high energy nuclear scattering, which treats the initial stage of heavy ion collisions in a sophisticated way. We are able to calculate macroscopic quantities like energy density and velocity flow at the end of this initial stage, after the two nuclei having penetrated each other. In other words, we provide the initial conditions for a macroscopic treatment of the second stage of the collision. We address in particular the question of how to incorporate the soft component properly. We find almost perfect "Bjorken scaling": the rapidity coincides with the space-time rapidity, whereas the transverse flow is practically zero. The distribution of the energy density in the transverse plane shows typically a very "bumpy" structure.Comment: 17 pages, 24 figure

Screening and Anti-Screening Effects in J/psi Production on Nuclei

The nuclear effects in J/psi hadro- and electroproduction on nuclei are considered in framework of reggeon approach. It is shown that screening regime which holds for electroproduction at x_F > 0.7 and for hadroproduction at x_F > -(0.3-0.4) is changed with anti-screening regime for smaller x_F values.Comment: 6 pages, 6 figures. Small changes in wordin

On the Role of Energy Conservation in High-Energy Nuclear Scattering

We argue that most commonly used models for nuclear scattering at ultra-relativistic energies do not treat energy conservation in a consistent fashion. Demanding theoretical consistency as a minimal requirement for a realistic model, we provide a solution for the above-mentioned problem, the so-called ``Parton-Based Gribov-Regge Theory''. In order to keep a clean picture, we do not consider secondary interactions. We provide a very transparent extrapolation of the physics of more elementary interactions towards nucleus-nucleus scattering, without considering any nuclear effects due to final state interactions. In this sense we consider our model a realistic and consistent approach to describe the initial stage of nuclear collisions.Comment: 17 pages, LaTeX created with LyX, 10 figure

Study of ππ\pi\pi correlations at LHC and RHIC energies in pppp collisions within the quark-gluon string model

The Quark Gluon String Model (QGSM) reproduces well the global characteristics of the $pp$ collisions at RHIC and LHC, e.g., the pseudorapidity and transverse momenta distributions at different centralities. The main goal of this work is to employ the Monte Carlo QGSM for description of femtoscopic characteristics in $pp$ collisions at RHIC and LHC. The study is concentrated on the low multiplicity and multiplicity averaged events, where no collective effects are expected. The different procedures for fitting the one-dimensional correlation functions of pions are studied and compared with the space-time distributions extracted directly from the model. Particularly, it is shown that the double Gaussian fit reveals the contributions coming separately from resonances and from directly produced particles. The comparison of model results with the experimental data favors decrease of particle formation time with rising collision energy.Comment: 9 pages, 14 figures, 2 table

Finite formation time effects in quasi-elastic (e,e′)(e,e') scattering on nuclear targets

The problem of the final state interaction in quasi-elastic $(e,e')$ scattering at large $Q^2$, is investigated by exploiting the idea that the ejected nucleon needs a finite amount of time to assume its asymptotic form. It is shown that when the dependence of the scattering amplitude of the ejected nucleon on its virtuality is taken into account, the final state interaction is decreased. The developed approach is simpler to implement than the one based on the color transparency description of the damping of the final state interaction, and is essentially equivalent to the latter in the case of the single rescattering term. The $(e,e')$ process on the deuteron is numerically investigated and it is shown that, at $x=1$, appreciable finite formation time effects at $Q^2$ of the order of 10 (GeV/c)$^2$ are expected.Comment: 23 pages, 3 figure