Energy dependence of particle ratio fluctuations in central Pb+Pb collisions from $\sqrt{s_{_{NN}}} =$~6.3 to 17.3 GeV

TL;DR

This study measures how particle ratio fluctuations in central Pb+Pb collisions vary with energy between 6.3 and 17.3 GeV, revealing non-statistical behavior and energy-dependent deviations from models.

Contribution

It provides the first detailed energy dependence of event-by-event particle ratio fluctuations in heavy ion collisions at CERN SPS energies.

Findings

K/pi fluctuations are larger than independent production at all energies.

(p + p̄)/pi fluctuations are smaller, indicating resonance decay correlations.

Fluctuation deviations increase at lower energies and are not well described by transport models.

Abstract

We present measurements of the energy dependence of event-by-event fluctuations in the K/pi and (p + \bar{p})/pi multiplicity ratios in heavy ion collisions at the CERN SPS. The particle ratio fluctuations were obtained for central Pb+Pb collisions at five collision energies, \sqrt{s_{_{NN}}}, between 6.3 and 17.3 GeV. After accounting for the effects of finite-number statistics and detector resolution, we extract the strength of non-statistical fluctuations at each energy. For the K/pi ratio, larger fluctuations than expected for independent particle production are found at all collision energies. The fluctuations in the (p + \bar{p})/pi ratio are smaller than expectations from independent particle production, indicating correlated pion and proton production from resonance decays. For both ratios, the deviation from purely statistical fluctuations shows an increase towards lower collision energies. The results are compared to transport model calculations, which fail to describe the energy dependence of the K/pi ratio fluctuations.