Factorial cumulants as a probe of fireball properties in heavy-ion collisions

We analyze joint factorial cumulants of protons and antiprotons in relativistic heavy-ion collisions. In the context of the critical point search, these provide advantages over the traditional cumulants, with interesting hints coming from RHIC-BES-II data. We also point out that the scaling $\hat{C}_{nm}^{p,\bar{p}} \propto \mean{p}^n \mean{\bar{p}}^m$ as a function of acceptance is obeyed if only long-range correlations are present in the system, such as global baryon conservation and volume fluctuations. This hypothesis can be directly tested experimentally without the need for corrections for volume fluctuations. The experimental data of the STAR Collaboration from phase I of RHIC beam energy scan points to a remarkably large splitting between protons and antiprotons, which is challenging to describe within a picture of a single fireball. The perspectives of analyzing acceptance dependence of high-order factorial cumulants within phase II of RHIC-BES are elaborated.