LHC13 forward elastic scattering: Dynamical gluon mass and semihard interactions.

In the context of a QCD-based model with even-under-crossing amplitude dominance at high-energies, it is shown that the $pp$ and $\bar{p}p$ elastic scattering data on $\sigma_{tot}$ and $\rho$ above 10 GeV are quite well described, especially the recent TOTEM data at 13 TeV. Specifically, we investigate the role of low-$x$ parton dynamics in dictating the high-energy behavior of forward scattering observables at LHC energies, by using a nonpertubative cutoff linked to the dynamical generation of a gluon mass. Unexpected features of the data, such as the rather small $\rho$ value at 13 TeV recently reported by the TOTEM Collaboration, are addressed using an eikonalized elastic amplitude, where unitarity and analyticity properties are readily build in. The model provides an accurate global description of $\sigma_{tot}$ and $\rho$ with pre- and post-LHC fine-tuned parton distributions, CTEQ6L and CT14, even if data at 8 and 13 TeV are not included in the dataset analyzed. These findings suggest that the low-$x$ parton dynamics, as well as the nonperturbative dynamics of QCD, play a major role in the driving mechanism behind the pre-asymptotic $\rho$ decrease at LHC energies.