Analysis and implications of precision near-forward TOTEM data

Very precise data on elastic proton-proton scattering at √s=7, 8 and 13 TeV have been obtained by the TOTEM group at LHC in the near-forward region (momentum transfers down to |t|=6×10^-4 GeV² at √s=8 and 13 TeV). The Coulomb-nuclear interference has been measured with sufficient accuracy for TOTEM to establish the falloff of the ρ parameter with increasing energy. The predictions from a previously studied model are shown to be in good agreement with the data and thus allow us to draw rather firm conclusions about the structure of the near-forward nuclear amplitude. We point out that due to a zero in the real part of the nuclear amplitude occurring at a very small momentum transfer---that can migrate into the Coulomb-nuclear interference (CNI) region at higher energies---much care is needed in extracting the numerical value of ρ for such energies. Thus, the true value of ρ would be higher than the TOTEM value for ρ found under the hypothesis that the real part of the elastic nuclear amplitude is devoid of such a zero in the CNI region.