System size dependence of particle-ratio fluctuations in Pb+Pb collisions at 158$A$ GeV

TL;DR

This paper reports on measurements of particle-ratio fluctuations in Pb+Pb collisions at 158A GeV, showing how these fluctuations depend on collision centrality and energy, and testing scaling models against the data.

Contribution

It provides new measurements of particle-ratio fluctuations and evaluates the applicability of multiplicity scaling scenarios across different centralities and energies.

Findings

Fluctuations increase from central to semi-peripheral collisions.

Scaling applies to some particle ratios but not all, especially where sign changes occur.

A universal scaling description does not fit all observed energy dependencies.

Abstract

New measurements by the NA49 experiment of the centrality dependence of event-by-event fluctuations of the particle yield ratios (K$^{+}$+K$^{-}$)/($\pi^{+}+\pi^{-}$), (p+$\bar{\text p}$)/($\pi^{+}+\pi^{-}$), and (K$^{+}$+K$^{-}$)/(p+$\bar{\text p}$) are presented for Pb+Pb collisions at 158$A$ GeV. The absolute values of the dynamical fluctuations of these ratios, quantified by the measure $\sigma_{\text{dyn}}$, increase by about a factor of two from central to semi-peripheral collisions. Multiplicity scaling scenarios are tested and found to apply for both the centrality and the previously published energy dependence of the (K$^{+}$+K$^{-}$)/($\pi^{+}+\pi^{-}$) and (p+$\bar{\text p}$)/($\pi^{+}+\pi^{-}$) ratio fluctuations. A description of the centrality and energy dependence of (K$^{+}$+K$^{-}$)/(p+$\bar{\text p}$) ratio fluctuations by a common scaling prescription is not possible since there is a sign change in the energy dependence.