Baryon fluctuation signatures of the onset of deconfinement

Abstract

An anomalous collision-energy dependence of proton number fluctuations is predicted as a consequence of the onset of deconfinement in heavy-ion collisions at the center of mass energy of the nucleon pair of about 10 GeV. The effect arises from changes in the effective degrees of freedom between confined and deconfined matter. This may provide a natural explanation of the recent beam-energy-scan results on proton number fluctuations at the BNL RHIC and offers a consistent interpretation of data from the CERN SPS and RHIC experiments in terms of the onset of deconfinement.

Figures (4)

• Figure 1: Collision energy dependence of the $\kappa_2[N]/\kappa_1[N]$ ratio predicted in the vicinity of the onset of deconfinement in heavy-ion collisions. Cumulants are calculated for the net baryon number within GCE ($N=B$), the net-baryon number within momentum acceptance taking into account net-baryon number conservation ($N=B_A$), and the proton number within the momentum acceptance ($N=p_A$). The lines indicated by light gray colour connect the HRG and QGP dependences across the changeover region to guide the eye.
• Figure 2: The same as in Fig. \ref{['fig:k2k1']} but for $\kappa_3[N]/\kappa_2[N]$
• Figure 3: The same as in Fig. \ref{['fig:k2k1']} but for $\kappa_4[N]/\kappa_2[N]$.
• Figure 4: Collision-energy dependence of the factorial cumulant ratios of the proton number in the acceptance. Symbols show measurements from the STAR experiment STAR:2025zdqBraun-Munzinger:2026krf, while solid lines correspond to our model calculations.