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

TL;DR

The paper develops a Monte Carlo generator for high-energy hadronic and nuclear collisions within Reggeon Field Theory, explicitly resumming enhanced Pomeron diagrams to all orders and separating soft and semihard parton dynamics via the semihard Pomeron. It introduces a probabilistic MC scheme grounded in positively-defined macro-configurations derived from unitarity cuts of cut enhanced diagrams, enabling iterative generation of complex final states. Key contributions include recursive Schwinger-Dyson representations for net-fan structures, a detailed sampling procedure for final-state topologies, and a parameter-calibrated set of results that align with experimental cross sections and forward observables. The approach provides a unitarity-consistent framework with direct links between total/elastic amplitudes and inelastic final states, with generalization to nucleus-nucleus collisions achieved without new parameters and implications for cosmic-ray air shower modeling and forward-physics at colliders.

Abstract

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.

Figures (24)

• Figure 1: General multi-Pomeron contribution to hadron-hadron scattering amplitude; elementary scattering processes correspond to Pomeron exchanges (vertical thick lines) or to Pomeron-Pomeron interactions.
• Figure 2: A "general Pomeron" (l.h.s.) consists of the soft and semihard ones - correspondingly the 1st and the 2nd contributions in the r.h.s.
• Figure 3: Recursive equation for projectile net-fan contribution $\chi_{a(j)|d(k)}^{{\rm net}}(y_{1},\vec{b}_{1}|Y,\vec{b})$; $y_{1}$ and $b_{1}$ are rapidity and impact parameter distances between the projectile proton and the vertex in the handle of the fan. The vertex $(y_{2},\vec{b}_{2})$ couples together $m_{2}$ projectile net-fans and $n_{2}$ target net-fans. In addition, there are $l\geq1$ irreducible 2-point sequences of Pomerons and Pomeron loops, exchanged between the vertices $(y_{1},\vec{b}_{1})$ and $(y_{2},\vec{b}_{2})$.
• Figure 4: Recursive representations for the contributions of irreducible 2-point sequences of Pomerons and Pomeron loops $\chi^{{\rm loop(1)}}$ (top) and $\chi^{{\rm loop}}$ (bottom), exchanged between the vertices $(y_{1},\vec{b}_{1})$ and $(y_{2},\vec{b}_{2})$.
• Figure 5: Recursive representations for cut net-fan diagrams characterized by a fanlike structure of cuts. The top line of the figure defines the contribution $2\hat{\chi}_{a(j)|d(k)}^{{\rm fan}}$ of the subset of graphs in which the handle of the fan is cut; the bottom line gives the one of the diagrams with uncut handle, $2\tilde{\chi}_{a(j)|d(k)}^{{\rm fan}}$.