Higher moments of multiplicity fluctuations in a hadron-resonance gas with exact conservation laws

Higher moments of multiplicity fluctuations of hadrons produced in central nucleus-nucleus collisions are studied within the hadron-resonance gas model in the canonical ensemble. Exact conservation of three charges, baryon number, electric charge, and strangeness is enforced in the large volume limit. Moments up to the fourth order of various particles are calculated at CERN Super Proton Synchrotron, BNL Relativistic Heavy Ion Collider (RHIC), and CERN Large Hadron Collider energies. The asymptotic fluctuations within a simplified model with only one conserved charge in the canonical ensemble are discussed where simple analytical expressions for moments of multiplicity distributions can be obtained. Moments products of net-proton, net-kaon, and net-charge distributions in Au + Au collisions at RHIC energies are calculated. The pseudorapidity coverage dependence of net-charge fluctuation is discussed.

Figure 1

(a) The products of the moments, ${\sigma }^2/M,S\sigma$, and $\kappa {\sigma }^2$, of different sets of primary hadrons, ${\pi }^{+},{\pi }^{-},K^{+},K^{-},p,\overline{p}$, positive ($N_{+}$), and negative ($N_{-}$) charged particles, in the CE HRG model at SPS, RHIC, and LHC energies. (b) Ratios of multiplicities of ${\pi }^{+},{\pi }^{-},K^{+},K^{-},p,\overline{p}$, positive, and negative charged particles with respect to multiplicities of all species carrying a nonvanishing value of the same charge, where $N_Q$ indicates multiplicity of particles with a nonzero electric charge, $N_{Q,S}$ a nonzero electric charge or strangeness, and $N_{Q,B}$ a nonzero electric charge or baryon number.

Figure 2

Energy dependence of the products of the moments, ${\sigma }^2/M,S\sigma /\mathrm{Skellam}$, and $\kappa {\sigma }^2$, for (a) net-proton, (b) net-kaon, and (c) net-charge distributions from the HRG model.

Figure 3

HRG model results for primordial and final state particles in both GCE and CE shown as different kinds of arrows compared with pseudorapidity coverage dependence of moments products, ${\sigma }^2/M,S\sigma$, and $\kappa {\sigma }^2$, for net-charge distributions obtained by STAR experiment [30] at $\sqrt{s_{NN}}=14.5$ GeV.