Model dependence of the number of participant nucleons and observable consequences in heavy-ion collisions

Abstract

Abstract The centrality determination and the estimated fluctuations of number of participant nucleons $$N_{part}$$ N part in Au–Au collisions at 1.23 AGeV beam kinetic energy suffers from severe model dependencies. Comparing the Glauber Monte Carlo (MC) and UrQMD transport models, it is shown that $$N_{part}$$ N part is a strongly model dependant quantity. In addition, for any given centrality class, Glauber MC and UrQMD predicts drastically different $$N_{part}$$ N part distributions. The impact parameter b and the number of charged particles $$N_{ch}$$ N ch on the other hand are much more correlated and give an almost model independent centrality estimator. It is suggested that the total baryon number balance, from integrated rapidity distributions, can be used instead of $$N_{part}$$ N part in experiments. Preliminary HADES data show significant differences to both, UrQMD simulations and STAR data in this respect.