Strongly Intensive Measures for Particle Number Fluctuations: Effects of Hadronic Resonances

Strongly intensive measures $\Delta$ and $\Sigma$ are used to study event-by-event fluctuations of hadron multiplicities in nucleus-nucleus collisions. The effects of resonance decays are investigated within statistical model and relativistic transport model. Two specific examples are considered: resonance decays to two positively charged particles (e.g., $\Delta^{++}\rightarrow p+ \pi^+$) and to $\pi^+\pi^-$-pairs. (e.g., $\rho^0\rightarrow \pi^-+\pi^+$). It is shown that resonance abundances at the chemical freeze-out can be estimated by measuring the fluctuations of the number of stable hadrons. These model results are compared to the full hadron-resonance gas analysis within both the grand canonical and canonical ensemble. The ultra-relativistic quantum molecular dynamics (UrQMD) model of nucleus-nucleus collisions is used to illustrate the role of global charge conservation, centrality selection, and limited experimental acceptance.