In nucleon-nucleon collisions, constituent-constituent interactions, such as the production of jets, W ’s, Z’s, Drell-Yan pairs, etc., favor small nucleon impact parameters with high spatial overlap, thereby enhancing the production of associated low-$p_t$ hadrons which make up the ‘‘underlying’’ event. We use a simple model, which reproduces the measured minimum-bias multiplicity distributions, to determine the multiplicity–impact-parameter relationship and to estimate the underlying event multiplicity in constituent-constituent interactions as compared with the minimum-bias multiplicity. Measurement of these distributions will reflect the spatial distribution of the hadron constituents.

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