Centrality definition using mid-rapidity ET distributions from p + Be to Au + Au at AGS energies

Measurements by the E802 Collaboration of the A-dependence and pseudorapidity interval (Sri) dependence of mid-rapidity Er distributions in a half-azimuth electromagnetic calorimeter are presented for p+Be, p+Au, O+Cu, Si+Au and Au+Au collisions at the BNL-AGS. The issues addressed are 1) whether the shapes of the upper edges of the Er distributions vary with delta eta similarly to the variation in shapes of mid-rapidity charged particle distributions and 2) hom small a delta eta interval would still give a meaningful characterization of the 'nuclear geometry' of a reaction. A new way of plotting ET distributions was found from which the reaction dynamics could be read directly.