Thermodynamic approach to proton number fluctuations in baryon-rich heavy-ion matter created at moderate collision energies

Abstract

We develop a framework to relate proton number cumulants measured in heavy-ion collisions within a momentum space acceptance to the susceptibilities of baryon number, assuming that particles are emitted from a fireball with uniform distribution of temperature and baryochemical potential, superimposed on a hydrodynamic flow velocity profile. The rapidity acceptance dependence of proton cumulants measured by the HADES Collaboration in $\sqrt{s_{\mathrm{NN}}}=2.4$ GeV Au-Au appears to be consistent with thermal emission of nucleons from a grand-canonical heat bath, with the extracted baryon number susceptibilities exhibiting an hierarchy ${\chi }_4^B\gg -{\chi }_3^B\gg {\chi }_2^B\gg {\chi }_1^B$. Naively, this could indicate large non-Gaussian fluctuations that might point to the presence of the QCD critical point close to the chemical freeze-out at $T\sim 70$ MeV and ${\mu }_B\sim 850-900$ MeV. However, the description of the experimental data at large rapidity acceptances becomes challenging once the effect of exact baryon number conservation is incorporated, suggesting that more theoretical and experimental studies are needed to reach a firm conclusion.

7 pages, 1 figure. v3: typos corrected, version published in Physics Letters B

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• Lattice QCD equation of state at finite chemical potential from an alternative expansion scheme
• Cumulants and Correlation Functions of Net-proton, Proton and Antiproton Multiplicity Distributions in Au+Au Collisions at energies available at the BNL Relativistic Heavy Ion Collider
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Cited by in corpus (6)

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• A model-free procedure to correct for volume fluctuations in E-by-E analyses of particle multiplicities
• Cooper-Frye sampling with short-range repulsion
• Possible origin of HADES data on proton number fluctuations in Au+Au collisions
• Fluctuations of conserved charges in hydrodynamics and molecular dynamics