  The Ultrarelativistic Quantum Molecular Dynamics [UrQMD] model is widely used
to simulate heavy ion collisions in broad energy ranges. It consists of various
components to implement the different physical processes underlying the
transport approach. A major building block are the shared tables of constants,
implementing the baryon masses and widths. Unfortunately, many of these input
parameters are not well known experimentally. In view of the upcoming physics
program at FAIR, it is therefore of fundamental interest to explore the
stability of the model results when these parameters are varied. We perform a
systematic variation of particle masses and widths within the limits proposed
by the particle data group (or up to 10%). We find that the model results do
only weakly depend on the variation of these input parameters. Thus, we
conclude that the present implementation is stable with respect to the
modification of not yet well specified particle parameters.
