Recent data from LHC13 by the TOTEM Collaboration on σ tot and ρ have indicated disagreement with all the Pomeron model predictions by the COMPETE Collaboration (2002). On the other hand, as recently demonstrated by Martynov and Nicolescu (MN), the new σ tot datum and the unexpected decrease in the ρ value are well described by the maximal Odderon dominance at the highest energies. Here, we discuss the applicability of Pomeron dominance through fits to the most complete set of forward data from pp andpp scattering. We consider an analytic parametrization for σ tot (s) consisting of non-degenerated Regge trajectories for even and odd amplitudes (as in the MN analysis) and two Pomeron components associated with double and triple poles in the complex angular momentum plane. The ρ parameter is analytically determined by means of dispersion relations. We carry out fits to pp andpp data on σ tot and ρ in the interval 5 GeV -13 TeV (as in the MN analysis). Two novel aspects of our analysis are: (1) the dataset comprises all the accelerator data below 7 TeV and we consider three independent ensembles by adding: either only the TOTEM data (as in the MN analysis), or only the ATLAS data, or both sets; (2) in the data reductions to each ensemble, uncertainty regions are evaluated through error propagation from the fit parameters, with 90 % CL. We argument that, within the uncertainties, this analytic model corresponding to soft Pomeron dominance, does not seem to be excluded by the complete set of experimental data presently available.
Recent data from LHC13 by the TOTEM Collaboration have indicated an unexpected decrease in the value of the ρ parameter and a σ tot value in agreement with the trend of previous measurements at 7 and 8 TeV. These data at 13 TeV are not simultaneously described by the predictions from Pomeron models selected by the COMPETE Collaboration, but show agreement with the maximal Odderon dominance, as recently demonstrated by Martynov and Nicolescu. Here we present a detailed analysis on the applicability of Pomeron dominance by means of a general class of forward scattering amplitude, consisting of even-under-crossing leading contributions associated with single, double and triple poles in the complex angular momentum plane and subleading even and odd Regge contributions. The analytic connection between σ tot and ρ is obtained by means of singly subtracted dispersion relations and we carry out fits to pp andpp data in the interval 5 GeV -13 TeV. The data set comprises all the accelerator data below 7 TeV and we consider two independent ensembles by adding either only the TOTEM data or TOTEM and ATLAS data at the LHC energy region. In the data reductions to each ensemble the uncertainty regions are evaluated with both one and two standard deviation (∼ 68 % and ∼ 95 % CL, respectively). Besides the general analytic model, we investigate four particular cases of interest, three of them typical of outstanding models in the literature. We conclude that, within the experimental and theoretical uncertainties and both ensembles, the general model and three particular cases are not able to describe the σ tot and ρ data at 13 TeV simultaneously. However, if the discrepancies between the TOTEM and ATLAS data are not resolved, one Pomeron model, associated with double and triple poles and with only 7 free parameters, seems not to be excluded by the complete set of experimental information presently available.
In the context of a QCD-based model with even-under-crossing amplitude dominance at highenergies, it is shown that the pp andpp elastic scattering data on σtot and ρ 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 ρ 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 σtot and ρ 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 ρ decrease at LHC energies.
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.
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