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

Jan Steinheimer,Yongjia Wang,Ayon Mukherjee,Yunxiao Ye,Chenchen Guo,Qingfeng Li,Horst Stoecker

doi:10.1016/j.physletb.2018.07.068

Abstract

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 Δy>0.4 the effects of global baryon number conservation dominate and all cumulant ratios are significantly smaller than 1.

Highlights

The effect of nuclear interactions on measurable net-proton number fluctuations in heavy ion collisions at the SIS18/GSI accelerator is investigated
To verify that fluctuations are affected by nuclear interactions, we first have to study the cumulant ratios for a fixed spatial volume, during the dynamical evolution of the system
We have shown that nuclear interactions can have a significant effect on the net-baryon number cumulant ratios in heavy ion collisions at SIS18 beam energies

Summary

Introduction

The effect of nuclear interactions on measurable net-proton number fluctuations in heavy ion collisions at the SIS18/GSI accelerator is investigated. In a grand canonical thermodynamic ensemble the cumulants of the net-charge distribution functions should diverge at the critical point of the phase transition, due to the divergence of the correlation length It was suggested, that the measurement of the net-proton number fluctuations in a fixed rapidity interval could reveal the onset of deconfinement and/or the critical endpoint of QCD. The systems created in these nuclear collisions are very small, rapidly expanding and a detailed understanding and interpretation of the measured moments is difficult due to uncertainties in the centrality determination, efficiency corrections and acceptance cuts To address these experimental uncertainties one employs models to simulate the dynamical expansion of the system created in the heavy ion collision.

Methods

Results

Conclusion