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

TL;DR

This paper investigates how resonance decays influence event-by-event fluctuations of hadron multiplicities in nucleus-nucleus collisions using strongly intensive measures, combining statistical, transport, and microscopic models.

Contribution

It demonstrates that resonance decay effects on fluctuations can be used to estimate resonance abundances at chemical freeze-out, integrating various models for comprehensive analysis.

Findings

Resonance decays significantly affect fluctuation measures.

Fluctuation measurements can estimate resonance abundances.

Model comparisons highlight the impact of conservation laws and acceptance.

Abstract

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.