Leading components in forward elastic hadron scattering: Derivative dispersion relations and asymptotic uniqueness

Abstract

Forward amplitude analyses constitute an important approach in the investigation of the energy dependence of the total hadronic cross-section ${\sigma }_{tot}$ and the $\rho$ parameter. The standard picture indicates for ${\sigma }_{tot}$ a leading log-squared dependence at the highest c.m. energies, in accordance with the Froissart-Lukaszuk-Martin bound. Beyond this log-squared (L2) leading dependence, other amplitude analyses have considered a log-raised-to-gamma form (L$\gamma$), with $\gamma$ as a real free fit parameter. In this case, analytic connections with $\rho$ can be obtained either through dispersion relations (derivative forms), or asymptotic uniqueness (Phragmén-Lindelöff theorems). In this work we present a detailed discussion on the similarities and mainly the differences between the Derivative Dispersion Relation (DDR) and Asymptotic Uniqueness (AU) approaches and results, with focus on the L$\gamma$ and L2 leading terms. We also develop new Regge-Gribov fits with updated dataset on ${\sigma }_{tot}$ and $\rho$ from $pp$ and $\bar{p}p$ scattering, in the region 5 GeV-8 TeV. The recent tension between the TOTEM and ATLAS results at 7 TeV and mainly 8 TeV is considered in the data reductions. Our main conclusions are: (1) all fit results present agreement with the experimental data analyzed and the goodness-of-fit is slightly better in case of the DDR approach; (2) by considering only the TOTEM data at the LHC region, the fits with L$\gamma$ indicate $\gamma \sim 2.0\pm 0.2$ (AU) and $\gamma \sim 2.3\pm 0.1$ (DDR); (3) by including the ATLAS data the fits provide $\gamma \sim 1.9\pm 0.1$ (AU) and $\gamma \sim 2.2\pm 0.2$ (DDR); (4) in the formal and practical contexts, the DDR approach is more adequate for the energy interval investigated than the AU approach. A review on the analytic results for ${\sigma }_{tot}$ and $\rho$ from the Regge-Gribov, DDR and AU approaches is presented.

Comments: 41 pages, 3 tables, 8 figures, misprints corrected, matches published version