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

The collaboration
Phys.Rev.Lett. 128 (2022) 202303, 2022.

Abstract (data abstract)
We report cumulants of the proton multiplicity distribution from dedicated fixed-target Au+Au collisions at $\sqrt{s_{NN}}$ = 3.0 GeV, measured by the STAR experiment in the kinematic acceptance of rapidity ($y$) and transverse momentum ($p_{T}$) within $-0.5 < y<0$ and $0.4 < p_{T} <2.0$ GeV/$c$. In the most central 0-5% collisions, a proton cumulant ratio is measured to be $C_4/C_2=-0.85 \pm 0.09 ~(\rm stat.) \pm 0.82 ~(\rm syst.)$, which is 2$\sigma$ 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.

• #### figure 1 data

Data from figure 1

10.17182/hepdata.115559.v1/t1

$\sqrt{s_{NN}}$ = 3.0 GeV data (black markers), GM (red histogram), and single and pile-up contributions from unfolding. Vertical lines on...

• #### figure 1 model

Model from figure 1

10.17182/hepdata.115559.v1/t2

$\sqrt{s_{NN}}$ = 3.0 GeV data (black markers), GM (red histogram), and single and pile-up contributions from unfolding. Vertical lines on...

• #### figure 3 Data w/o VFC

Data from figure 3

10.17182/hepdata.115559.v1/t3

• #### figure 3 UrQMD calculation

Data from figure 3

10.17182/hepdata.115559.v1/t5