We report the beam energy and collision centrality dependence of fifth and sixth order cumulants (C_{5}, C_{6}) and factorial cumulants (κ_{5}, κ_{6}) of net-proton and proton number distributions, ...from center-of-mass energy (sqrts_{NN}) 3 GeV to 200 GeV Au+Au collisions at RHIC. Cumulant ratios of net-proton (taken as proxy for net-baryon) distributions generally follow the hierarchy expected from QCD thermodynamics, except for the case of collisions at 3 GeV. The measured values of C_{6}/C_{2} for 0%-40% centrality collisions show progressively negative trend with decreasing energy, while it is positive for the lowest energy studied. These observed negative signs are consistent with QCD calculations (for baryon chemical potential, μ_{B}≤110 MeV) which contains the crossover transition range. In addition, for energies above 7.7 GeV, the measured proton κ_{n}, within uncertainties, does not support the two-component (Poisson+binomial) shape of proton number distributions that would be expected from a first-order phase transition. Taken in combination, the hyperorder proton number fluctuations suggest that the structure of QCD matter at high baryon density, μ_{B}∼750 MeV at sqrts_{NN}=3 GeV is starkly different from those at vanishing μ_{B}∼24 MeV at sqrts_{NN}=200 GeV and higher collision energies.
Here we present high-precision measurements of elliptic, triangular, and quadrangular flow v2, v3, and v4, respectively, at midrapidity for identified hadrons π, p, K, φ, Ks, Λ as a function of ...centrality and transverse momentum in Au+Au collisions at the center-of-mass energy √sNN = 200 GeV. We observe similar vn trends between light and strange mesons which indicates that the heavier strange quarks flow as strongly as the lighter up and down quarks. The number-of-constituent-quark scaling for v2, v3, and v4 is found to hold within statistical uncertainty for 0–10%, 10–40%, and 40–80% collision centrality intervals. The results are compared to several viscous hydrodynamic calculations with varying initial conditions, and could serve as an additional constraint to the development of hydrodynamic models.
Elliptic flow measurements from two-, four-, and six-particle correlations are used to investigate flow fluctuations in collisions of U+U at sqrts_{NN}=193 GeV, Cu+Au at sqrts_{NN}=200 GeV and ...Au+Au spanning the range sqrts_{NN}=11.5-200 GeV. The measurements show a strong dependence of the flow fluctuations on collision centrality, a modest dependence on system size, and very little if any, dependence on particle species and beam energy. The results, when compared to similar LHC measurements, viscous hydrodynamic calculations, and trento model eccentricities, indicate that initial-state-driven fluctuations predominate the flow fluctuations generated in the collisions studied.
The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di-π0s produced at forward pseudorapidities (2.6<η<4.0) in p+p, p+Al, and p+Au collisions at a center-of-mass ...energy of 200 GeV. We observe a clear suppression of the correlated yields of back-to-back π0 pairs in p+Al and p+Au collisions compared to the p+p data. The observed suppression of back-to-back pairs as a function of transverse momentum suggests nonlinear gluon dynamics arising at high parton densities. Furthermore, the larger suppression found in p+Au relative to p+Al collisions exhibits a dependence of the saturation scale $Q^{2}_{s}$ on the mass number A . A linear scaling of the suppression with A1/3 is observed with a slope of -0.09±0.01.
In this work, 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 (pT) within -0.5 < y < 0 and 0.4 < pT < 2.0 GeV/c. In the most central 0–5% collisions, a proton cumulant ratio is measured to be C4/C2 = –0:85 ± 0:09 (stat:)±0:82 (syst:), which is 2σ below the Poisson baseline with respect to both the statistical and systematic uncertainties. The hadronic transport UrQMD model reproduces our C4/C2 in the measured acceptance. Compared to higher energy results and the transport model calculations, the suppression in C4/C2 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.
We report cumulants of the proton multiplicity distribution from dedicated fixed-target Au+Au collisions at sqrts_{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±0.09 (stat)±0.82 (syst), which is 2σ 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.
In high-energy heavy-ion collisions, partonic collectivity is evidenced by the constituent quark number scaling of elliptic flow anisotropy for identified hadrons. A breaking of this scaling and ...dominance of baryonic interactions is found for identified hadron collective flow measurements in $\sqrt{^{S}\text{NN}}$ = 3 GeV Au+Au collisions. In this paper, we report measurements of the first- and second-order azimuthal anisotropic parameters, v1 and v2, of light nuclei (d, t, 3He, 4He) produced in $\sqrt{^{S}\text{NN}}$ = 3 GeV Au+Au collisions at the STAR experiment. An atomic mass number scaling is found in the measured v1 slopes of light nuclei at mid-rapidity. For the measured v2 magnitude, a strong rapidity dependence is observed. Unlike v2 at higher collision energies, the v2 values at mid-rapidity for all light nuclei are negative and no scaling is observed with the atomic mass number. Calculations by the Jet AA Microscopic Transport Model (JAM), with baryonic mean-field plus nucleon coalescence, are in good agreement with our observations, implying baryonic interactions dominate the collective dynamics in 3 GeV Au+Au collisions at RHIC.
Zooplankton plays an important role in aquatic food webs and changes in its abundance and diversity under changing climatic conditions can significantly affect the abundance and diversity of other ...aquatic organisms. The aim of the study was to assess quantitative and qualitative parameters of zooplankton development, dynamics of development of its dominant groups and the effect of water temperature. Species composition and abundance of zooplankton of the Kremenchuk Reservoir were studied in 2006, 2010-2012 and 2020 in relation to water temperature and pollution. Zooplankton species diversity fluctuated significantly over the years of the study. A total of 46 taxa were recorded in the reservoir during the study period. The number of recorded zooplankton taxa ranged 26 to 32 depending on the year. The most abundant zooplankters were Chydorus sphaericus, Copepoda nauplii, Brachionus diversicornis. The abundance of zooplankters in the reservoir during the study period ranged 23·(10)3 to 256·(10)3 ind./m3, and biomass 0.14 to 0.89 g/m3. A significant positive relationship was observed between the abundance of cladocerans, including some individual species (Ch. sphaericus and Ceriodaphnia sp.), and water temperature. Indicator species of water pollution in different years and in different parts of the Kremenchuk Reservoir differed significantly, which probably depended on the presence or absence (in a certain period of time) of polluting discharges. The total saprobity index in different years in different parts of the reservoir was in the range of 1.5-1.9. Structural indicators of zooplankton and its dominant complexes characterize the water in the Kremenchuk Reservoir as β-mesosaprobic. It is probably too early to assess the impact of climate change zooplankton as these changes are still unstable and short in time, but it is necessary to constantly monitor the biota of aquatic eco-systems to further study and summarize the data, which could later allow an identification of such changes.
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