System-size and energy dependence of particle momentum spectra: The UrQMD analysis of p plus p and Pb plus Pb collisions

The ultrarelativistic quantum molecular dynamics (UrQMD) transport model is used to study a system-size and energy dependence of the pion production in high energy collisions. New data of the NA61/SHINE Collaboration on spectra of negatively charged pions in proton-proton interactions at Super Proton Synchrotron (SPS) energies are considered. These results are compared with the corresponding data of the NA49 Collaboration in central Pb + Pb collisions at the same collision energies per nucleon. Mean pion multiplicity per participant nucleon, inverse slope parameter of the transverse momentum spectra, and width of rapidity distribution are investigated. A role of isospin effects is discussed. We find that the UrQMD model predicts a nonmonotonous behavior of mean transverse mass with collision energy for positively charged pions at mid-rapidity in inelastic proton-proton interactions. This will be checked soon experimentally by the NA61/SHINE Collaboration.