Experimental data on the moments of net-proton distribution in central Au-Au
collisions for various center of mass energies (sNN​​)
measured by the STAR collaboration at the Relativistic Heavy-Ion Collider
(RHIC) are compared to the corresponding results from a van der Waals type
interacting hadron resonance gas (VDWHRG) model. The parameters representing
the attractive and repulsive interactions in the VDWHRG model have been
extracted by fitting the σ2/M, Sσ and
κσ2, where M is the mean, σ is the standard deviation,
S is the skewness and κ the kurtosis of the net-proton
distribution. Considering all the three moment products we observe that the
strength of the repulsive interactions increases with decrease in
sNN​​ = 200 to 19.6 GeV while the strength of the
attractive interaction is of the similar magnitude. For sNN​​ = 11.5 and 7.7 GeV there is drop in the strength of both attractive
and repulsive interactions relative to sNN​​ = 19.6 GeV. On
the other hand, if we consider only the higher order moment products,
Sσ and κσ2, which are more sensitive to critical
point physics, a segregation with respect to the strength of the attractive
parameter is observed. The data for sNN​​ = 19.6 and 27 GeV
supports a larger attractive strength compared to other energies. For this
latter case, the repulsive interaction values are of similar order for most of
the beam energies studied, except for 7.7 GeV where the parameter value is not
well constrained due to large uncertainties