  The diffraction slope parameter is investigated for elastic proton-proton and
proton-antiproton scattering based on the all available experimental data at
low momentum transfer values. Energy dependence of the elastic diffraction
slopes is approximated by various analytic functions. The expanded "standard"
logarithmic approximations allow to describe experimental slopes in all
available energy range reasonably. Various approximations differ from each
other both in the low energy and very high energy domains. Predictions for
diffraction slope parameter are obtained for elastic proton-proton scattering
at RHIC and LHC energies, for proton-antiproton elastic reaction in FAIR energy
domain for various approximation functions.
