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

The STAR 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

    Centrality dependence of the proton cumulant ratios for Au+Au collisions at $\sqrt{s_{NN}}$ = 3.0 GeV. Protons are from $-0.5 <...

  • figure 3 Data w/ VFC

    Data from figure 3

    10.17182/hepdata.115559.v1/t4

    Centrality dependence of the proton cumulant ratios for Au+Au collisions at $\sqrt{s_{NN}}$ = 3.0 GeV. Protons are from $-0.5 <...

  • figure 3 UrQMD calculation

    Data from figure 3

    10.17182/hepdata.115559.v1/t5

    Centrality dependence of the proton cumulant ratios for Au+Au collisions at $\sqrt{s_{NN}}$ = 3.0 GeV. Protons are from $-0.5 <...

  • figure 4 Data w/o VFC rapidity dependence

    Data from figure 4

    10.17182/hepdata.115559.v1/t6

    Rapidity and transverse momentum dependence of the proton cumulant ratios for 0–5% central collisions. Black-squares, red-dots and blue-triangles stand for...

  • figure 4 Data w/o VFC pT dependence

    Data from figure 4

    10.17182/hepdata.115559.v1/t7

    Rapidity and transverse momentum dependence of the proton cumulant ratios for 0–5% central collisions. Black-squares, red-dots and blue-triangles stand for...

  • figure 4 Data w/ VFC rapidity dependence

    Data from figure 4

    10.17182/hepdata.115559.v1/t8

    Rapidity and transverse momentum dependence of the proton cumulant ratios for 0–5% central collisions. Black-squares, red-dots and blue-triangles stand for...

  • figure 4 Data w/ VFC pT dependence

    Data from figure 4

    10.17182/hepdata.115559.v1/t9

    Rapidity and transverse momentum dependence of the proton cumulant ratios for 0–5% central collisions. Black-squares, red-dots and blue-triangles stand for...

  • figure 5

    Data from figure 5

    10.17182/hepdata.115559.v1/t10

    Collision energy dependence of the ratios of cumulants, $C_4/C_2$, for proton (squares) and net-proton (red circles) from top 0-5% Au+Au...

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