We calculate volume-independent ratios of cumulants of the net-proton number distribution up to sixth order in a fireball that cools down after the chemical freeze-out. A hadron resonance gas model is used together with the assumption of partial chem
ical equilibrium, which fixes the number of observed stable hadrons after the chemical freeze-out. It is shown that due to only weak departure from the statistical Boltzmann distribution, also the volume-independent ratios of higher-order cumulants of the net-proton number show only weak dependence on the temperature. This observation supports the possibility to measure non-critical cumulants at chemical freeze-out even after subsequent cooling in the hadronic phase. Cumulants of the net-baryon number behave similarly, while those for the kaon number vary more strongly with the temperature. Our results are relevant for the current fluctuation studies of the RHIC-BES runs.
We present a calculation of the elliptic flow and azimuthal dependence of the correlation radii in the ellipsoidally symmetric generalization of the Buda-Lund model. The elliptic flow is shown to depend only on the flow anisotropy while in case of co
rrelation radii both flow and space anisotropy play an important role in determining their azimuthal oscillation. We also outline a simple procedure for determining the parameters of the model from data.
We present a few estimates of energy densities reached in heavy-ion collisions at the CERN SPS. The estimates are based on data and models of proton-nucleus and nucleus-nucleus interactions. In all of these estimates the maximum energy density in cen
tral Pb+Pb interactions is larger than the critical energy density of about 0.7 GeV/fm^3 following from lattice gauge theory computations. In estimates which we consider as realistic the maximum energy density is about twice the critical value. In this way our analysis gives some support to claims that deconfined matter has been produced at the CERN SPS. Any definite statement requires a deeper understanding of formation times of partons and hadrons in nuclear collisions. We also compare our results with implicit energy estimates contained in earlier models of anomalous J/psi suppression in nuclear collisions.
We complete the introduction of Yano-Koonin-Podgoretskii (YKP) parametrization of the correlation function by deriving the corrections to the correlation radii which arise from releasing the popular smoothness approximation and approximation of setti
ng the pair momentum on-shell. We investigate the definition range of this parametrization and find kinematic regions in which the YKP parametrization is inapplicable. These problems disappear if the newly proposed Modified Yano-Koonin-Podgoretskii parametrization is used. We then focus on the physical interpretation of the correlation radii obtained in the different parametrizations. While the extraction of the longitudinal source expansion from the YK rapidity is found to be rather robust against variations of the source density profiles, the extracted emission duration is quite sensitive to such variations and cannot be reliably extracted except for the case of extremely long source lifetimes.
