The role of mean free paths of product particles in high-energy nuclear collisions has been studied. In inclusive energy spectra the observed slope difference among $p$, $\pi$, and $K^{+}$ can be interpreted as due to the difference in mean free paths of these particles, suggesting that particles with longer mean free paths probe most sensitively the early, highly excited, hot phase of the collision. With use of the data of $\mathrm{pp}$ and $\pi \pi$ interferometries further discussions on the space-time evolution of the system are developed.

• Received 20 August 1982

DOI:https://doi.org/10.1103/PhysRevLett.49.1383