Global Dirac phenomenology for proton-nucleus elastic scattering

Energy-dependent global Dirac optical model potentials are found by fitting proton elastic scattering data in the energy range 20–1040 MeV for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. Three different energy- and atomic-mass-number-dependent global Dirac optical potentials are also obtained. A number of characteristic features of the potentials are discussed. In addition, the mean free path, the effective mass ${\mathit{m}}_{\mathit{e}}^{\mathrm{*}}$, the Dirac mass ${\mathit{M}}^{\mathrm{*}}$, and the relativistic energy shift ${\mathit{E}}^{\mathrm{*}}$ are calculated.