Pion production in nuclear collisions with Fermi motion effects

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Abstract
The independent multiple collision model for pion production in nuclear collisions is extended to include the effects of Fermi motion. We have developed an analytic expression for the distribution of invariant mass for colliding nucleons whose momentum distributions are in relative motion. This expression is tractable if the colliding distributions are described in terms of Gaussian functions. We make use of this formalism to calculate Fermi averaged cross sections for pion production, using as input multi-Gaussian fits to momentum distributions obtained from nuclear structure calculations. We have calculated charged pion multiplicity distributions and inclusive cross sections for proton-nucleus and nucleus-nucleus collisions. We use a phenomenological method for incorporating the effects of energy loss by participant nucleons and pion reabsorption. Sample calculations are presented and compared with available experimental data. We discuss the striking effect of Fermi motion on pion production at bombarding energies below the nucleon-nucleon pion production threshold.