Large proton cumulants from the superposition of ordinary multiplicity distributions

We construct a multiplicity distribution characterized by large factorial cumulants (integrated correlation functions) from a simple combination of two ordinary multiplicity distributions characterized by small factorial cumulants. We find that such a model, which could be interpreted as representing two event classes, reproduces the preliminary data for the proton cumulants measured by the STAR collaboration at 7.7 GeV very well. This model then predicts very large values for the fifth and sixth order factorial cumulants, which can be tested in experiment.

Figure 1

The multiplicity distribution $P\left(N\right)$ at $\sqrt{s_{NN}}=7.7\mathrm{GeV}$ in the two component model given by Eq. (1) constructed with (a) efficiency unfolded values for $\langle N\rangle ,C_3$ and $C_4$ and (b) with imposed efficiency of 0.65.

Figure 2

$P\left(N\right)$ for 7 GeV and twice the rapidity coverage as the present preliminary STAR data. See text for details.

Figure 3

(a) Transverse momentum distributions of charged pions from the UrQMD transport model. (b) Elliptic flow of charged pions as a function of the transverse momentum from UrQMD simulations. In both plots three different event selections are compared. The black solid lines correspond to all most central ($0–5\%$) events, while the red short dashed lines depict only most central events with a small proton number ($N<25$). The blue dashed lines correspond to the reference events with exactly 25 protons, but selected from all centralities.

Figure 4

Probability distribution at various points close to the co-existence line for the van der Waals model for system at fixed volume: $(T/T_c,\mu /{\mu }_c)=(1.02,0.99)$ (a), (1.02, 1.004) (b), (0.98, 1.0015) (c), (0.98, 1.004) (d), (0.95, 1.0062) (e). The model and parameters are described in Appendix pp2.