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NA61/SHINE results on multiplicity and net-charge fluctuations at CERN SPS energies

Maćkowiak-Pawłowska

TL;DR

NA61/SHINE investigates the QCD phase structure by analyzing multiplicity and net-charge fluctuations across system sizes and energies, focusing on Ar+Sc collisions at $\sqrt{s_{\mathrm{NN}}}=5.1$--$16.8$ GeV to search for critical-point signatures or onset of deconfinement. The study uses higher-order cumulants, centrality selection via the PSD calorimeter, and unfolding for detector biases, comparing to p+p and EPOS1.99 predictions. Key findings include hints of non-monotonic behavior in certain cumulant ratios and a notable deviation in multiplicity, but statistics are insufficient for a firm CP claim; EPOS1.99 matches magnitudes but not qualitative trends. These results contribute to mapping fluctuation observables across SPS energies and system sizes, informing the ongoing search for the critical point and the onset of deconfinement.

Abstract

This contribution presents final results on the energy dependence of multiplicity and net-electric charge fluctuations in Ar+Sc interactions collected by the NA61/SHINE experiment. Fluctuations were analyzed using higher-order cumulant ratios in Ar+Sc most central collisions and compared to p+p interactions. The results consider detector bias and centrality selection in the case of Ar+Sc. The results are compared across different energies and against model predictions.

NA61/SHINE results on multiplicity and net-charge fluctuations at CERN SPS energies

TL;DR

NA61/SHINE investigates the QCD phase structure by analyzing multiplicity and net-charge fluctuations across system sizes and energies, focusing on Ar+Sc collisions at -- GeV to search for critical-point signatures or onset of deconfinement. The study uses higher-order cumulants, centrality selection via the PSD calorimeter, and unfolding for detector biases, comparing to p+p and EPOS1.99 predictions. Key findings include hints of non-monotonic behavior in certain cumulant ratios and a notable deviation in multiplicity, but statistics are insufficient for a firm CP claim; EPOS1.99 matches magnitudes but not qualitative trends. These results contribute to mapping fluctuation observables across SPS energies and system sizes, informing the ongoing search for the critical point and the onset of deconfinement.

Abstract

This contribution presents final results on the energy dependence of multiplicity and net-electric charge fluctuations in Ar+Sc interactions collected by the NA61/SHINE experiment. Fluctuations were analyzed using higher-order cumulant ratios in Ar+Sc most central collisions and compared to p+p interactions. The results consider detector bias and centrality selection in the case of Ar+Sc. The results are compared across different energies and against model predictions.

Paper Structure

This paper contains 2 sections, 4 figures.

Table of Contents

  1. Introduction
  2. Results

Figures (4)

  • Figure 1: The $E_{\rm{PSD}}$ distribution used for centrality selection in Ar+Sc collisions at 75$A\,\hbox{Ge V}/ c$ (left) and the net-charge distribution in the 1% most central Ar+Sc collisions at 150$A\,\hbox{Ge V}/ c$ (right). The vertical line in the left panel indicates the selection threshold corresponding to the 1% most central events (lowest $E_{\rm{PSD}}$). In the right panel, the open circles correspond to the measured distribution, whereas full circles indicate the corrected distribution.
  • Figure 2: Energy dependence of intensive quantities of net-charge fluctuations in Ar+Sc collisions NA61SHINE:2025whi compared to published p+pSHINE:2023ejm and preliminary Be+Be results Mackowiak-Pawlowska:2020glz. Vertical bars denote statistical uncertainties, and vertical arrows -- systematic ones. Gray lines indicate the reference values.
  • Figure 3: Energy dependence of intensive quantities of positively charged hadron cumulant ratios in Ar+Sc collisions compared to published p+pSHINE:2023ejm. Vertical bars denote statistical uncertainties, and color bands -- systematic ones. Gray lines indicate the reference values NA61SHINE:2025whi.
  • Figure 4: Comparison of the energy dependence of intensive quantities of net-charge distribution in Ar+Sc collisions (triangles) with EPOS1.99 model (line). Vertical bars denote statistical uncertainties, and color bands -- systematic ones. Gray lines indicate the reference values.