Unfolding Baryon Number Fluctuations from Correlations of Light Nuclei Production in Heavy-Ion Collisions

TL;DR

This paper proposes a method to extract neutron fluctuations from light nuclei correlations in heavy-ion collisions, enabling better probing of the QCD critical point despite experimental limitations.

Contribution

It introduces a novel approach to unfold neutron fluctuations from light nuclei correlations, validated by model calculations, extending to third-order cumulants.

Findings

Baryon number fluctuations can be unfolded up to third order.

Uncertainties increase significantly for fourth and higher-order cumulants.

Model calculations support the feasibility of the proposed method.

Abstract

Event-by-event fluctuations of the baryon number, which is mostly carried by protons and neutrons, in relativistic heavy-ion collisions provide a sensitive probe for locating the conjectured critical point in the quantum chromodynamics (QCD) phase diagram. Since current experiments have limited access to neutron fluctuations because detectors are largely insensitive to neutrons, measurements of (net-)proton fluctuations are often used as a proxy for (net-)baryon number fluctuations. Although direct measurements of neutron fluctuations are challenging, their information are encoded in the production and correlations of light nuclei, when they are formed through coalescence of nucleons at kinetic freeze-out. Here, we propose to unfold neutron fluctuations from correlations among light nuclei produced in heavy-ion collisions. Model calculations validate this approach and show that baryon number fluctuations can be unfolded up to the third order. For fourth and higher-order cumulants, however, the uncertainties become sizable, indicating that further methodological developments and refinements are required.