Nonperturbative QCD effects in forward scattering at the LHC

Abstract

We study infrared contributions to semihard parton-parton interactions by considering an effective charge whose finite infrared behavior is constrained by a dynamical mass scale. Using an eikonal QCD-based model in order to connect this semihard parton-level dynamics to the hadronhadron scattering, we obtain predictions for the proton-proton (pp) and antiproton-proton (pp) total cross sections, σ pp,pp tot , and the ratios of the real to imaginary part of the forward scattering amplitude, ρ pp,pp . We discuss the theoretical aspects of this formalism and consider the phenomenological implications of a class of energy-dependent form factors in the high-energy behavior of the forward amplitude. We introduce integral dispersion relations specially tailored to relate the real and imaginary parts of eikonals with energy-dependent form factors. Our results, obtained using a group of updated sets of parton distribution functions (PDFs), are consistent with the recent data from the TOTEM, AUGER and Telescope Array experiments.

Exclusive production of pions and the pion distribution amplitude

“…which is an infrared finite coupling determined in QCD where gluons have an effective dynamical mass M g [41], with an infrared value M g (0) ≈ 2Λ QCD , consistent with the models of Ref. [33,36,37,42]. Λ QCD is the QCD characteristic scale.…”

Forward elastic scattering: dynamical gluon mass and semihard interactions

“…where W SH (s, b) is the overlap density distribution of semihard parton scattering, σ QCD denotes the cross section of hard parton scattering in the region where pQCD can be safely applied, namely above the cutoff Q 2 min . We assume (as in previous studies [37]) that hard parton scattering configuration in the transverse plane of the collision (in b-space) to be given by the Fourier-Bessel transform:…”

“…However, these processes are potentially divergent at low transferred momenta, and for this reason they must be regularized by means of some cutoff procedure. In a nonperturbative QCD context, one natural regulator was introduced by Cornwall some time ago [33], and since then has become an important feature in eikonalized models [34][35][36][37][38]. This regularization process is based on the increasing evidence that the gluon may develop a momentum-dependent mass, which introduces a natural scale able to separate the perturbative from the nonperturbative QCD region.…”

Inelastic cross sections, overlap functions and ${C}_{q}$ moments from ISR to LHC energies in proton interactions

“…We note that parton-parton scattering processes containing at least one gluon in the initial state are important to compute the QCD cross sections. In this respect and as discussed in [45], the gluon-gluon (  gg gg) and quark-gluon (  qg qg) scattering in fact dominate at high energies.…”