Correlated stopping, proton clusters and higher order proton cumulants

Understand

We investigate possible effects of correlations between stopped nucleons on higher order proton cumulants at low energy heavy-ion collisions.

• We find that fluctuations of the number of wounded nucleons $N_{\mathrm{part}}$ lead to rather nontrivial dependence of the correlations on the centrality; however, this effect is too small to explain the large and positive four-proton correlations found in the preliminary data collected by the STAR collaboration at $\sqrt{s}=7.7$ GeV.
• We further demonstrate that, by taking into account additional proton clustering, we are able to qualitatively reproduce the preliminary experimental data.
• We speculate that this clustering may originate either from collective/multi-collision stopping which is expected to be effective at lower energies or from a possible first-order phase transition, or from (attractive) final state interactions.