Pion Reabsorption in the Nuclear Matter: A Simple Model

The paper raises the problem of reabsorption of neutral pions in nuclear matter. Sophisticated transport models are unable to reconstruct the energy spectra and angular distributions of subthreshold particles. In order to reproduce angular distributions of subthreshold pions we have developed a simple, geometrical model and have tried to compare its predictions to the wealth of experimental data. Although the assumptions of the model are very simple, the agreement between data and the model results is generally very good. The angular distribution of primordial pions was described by the formula 1 + A2P2(cosυ). For each data set the A2 parameter was determined from the comparison to experimental distribution. No apparent trend is observed and we concluded that the angular distribution of primordial pions has a universal value of A2 parameter. (author)