Measurements of Proton High-Order Cumulants in sNN=3 GeV Au+Au Collisions and Implications for the QCD Critical Point

Résumé fourni par la source

We report cumulants of the proton multiplicity distribution from dedicated fixed-target $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=3.0\text{ }\text{ }\mathrm{GeV}$, measured by the STAR experiment in the kinematic acceptance of rapidity ($y$) and transverse momentum (${p}_{T}$) within $\ensuremath{-}0.5<y<0$ and $0.4<{p}_{T}<2.0\text{ }\text{ }\mathrm{GeV}/c$. In the most central 0%--5% collisions, a proton cumulant ratio is measured to be ${C}_{4}/{C}_{2}=\ensuremath{-}0.85\ifmmode\pm\else\textpm\fi{}0.09\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.82\text{ }(\mathrm{syst})$, which is $2\ensuremath{\sigma}$ below the Poisson baseline with respect to both the statistical and systematic uncertainties. The hadronic transport UrQMD model reproduces our ${C}_{4}/{C}_{2}$ in the measured acceptance. Compared to higher energy results and the transport model calculations, the suppression in ${C}_{4}/{C}_{2}$ is consistent with fluctuations driven by baryon number conservation and indicates an energy regime dominated by hadronic interactions. These data imply that the QCD critical region, if created in heavy-ion collisions, could only exist at energies higher than 3 GeV.

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