Nuclear interactions and net-proton number fluctuations in heavy ion collisions at the SIS18 accelerator

The effect of nuclear interactions on measurable net-proton number fluctuations in heavy ion collisions at the SIS18/GSI accelerator is investigated. The state of the art UrQMD model including interaction potentials is employed. It is found that the nuclear forces enhance the baryon number cumulants, as predicted from grand canonical thermodynamical models. The effect however is smeared out for proton number fluctuations due to iso-spin randomization and global baryon number conservation, which decreases the cumulant ratios. For a rapidity acceptance window larger than $\Delta y> 0.4$ the effects of global baryon number conservation dominate and all cumulant ratios are significantly smaller than 1.