Fluctuations In Au Research Articles

Collective behavior in proton number fluctuations seen in [formula omitted] 2.4 GeV Au+Au collisions

At energies of a few GeV per nucleon, nuclear collisions exhibit phenomena more complex than the individualistic nucleon interactions observed at much higher energies. From recent results on proton number fluctuations in Au+Au collisions at sNN=2.4 GeV obtained by the HADES experiment at GSI, we suggest that measuring the multiplicity distributions heavy-ion collisions can be used to probe density fluctuations associated with correlation phenomena. Using the combinant analysis, we demonstrate that the proton multiplicity distributions can be described by a compound Poisson-binomial distribution, suggesting the formation of clusters as a possible mechanism of such proton number fluctuations.

Characterization of deep ore-forming fluid in the Zhaoxian gold deposit within the Jiaodong gold province: insights from quartz vein fluid inclusion, in-situ trace element analysis, and S isotopic composition in pyrite

The Jiaodong gold province, situated in the southeastern margin of the North China Craton, is globally renowned for its substantial gold reserves exceeding 5,000 tonnes. The Zhaoxian gold deposit is part of the significant Jiaojia gold belt within the Jiaodong gold province. Fieldwork has identified four distinct stages of ore formation in this study: an early barren quartz vein stage (Stage 1) containing fine-grained pyrite; a gold-bearing stage (Stage 2) consisting of quartz, pyrite, and native gold; a polymetallic sulfide-rich stage (Stage 3) comprising quartz, polymetallic sulfides, and native gold; and a late-stage (Stage 4) primarily composed of quartz and calcite with minimal pyrite content. We conducted fluid inclusion analysis using microthermometry and Raman spectroscopy techniques to examine the fluid characteristics. In-situ analysis of trace elements in pyrite was performed to investigate the fluid composition and evolution. Additionally, we determined the sulfur isotope composition in pyrite to analyze the source of sulfur. Our findings indicate that the ore-forming fluid in the Zhaoxian gold deposit belongs to a medium-to-low-salinity H₂O-NaCl-CO₂-CH₄ system. Fluctuations in Au and As concentrations observed along with oscillating zones and sulfide inclusions during Stage 2 suggest potential fluid boiling processes occurring during mineralization. High concentrations of Ag, Cu, Zn, Cd, In, Pb, and Bi without oscillating zones during Stage 3 imply precipitation of polymetallic sulfides under stable fluid conditions. The δ34S values observed in the Zhaoxian gold deposit are slightly higher than those found in granitoids from other areas within Jiaodong but similar to those seen in other deposits within the Jiaojia gold belt region. In conclusion, magmatic-hydrothermal ore-forming fluids were involved along with significant fluid-rock interaction during metallogenic processes of the Zhaoxian gold deposit.

Direct observation of concentration fluctuations in Au–Si eutectic liquid by small-angle neutron scattering

It is well-known that eutectic gold–silicon (Au–Si) alloys exhibit anomalous melting point depression, which is more than 1000 °C from the melting point of elemental Si (1414 °C). The melting point depression in eutectic alloys is generally explained in terms of a decrease of the free energy by mixing. However, it is difficult to understand the anomalous melting point depression only from the stability of the homogeneous mixing. Some researchers suggest that there are concentration fluctuations in the liquids, where the atoms are inhomogeneously mixed. In this paper, we measure the small-angle neutron scattering (SANS) of Au81.4Si18.6 (eutectic composition) and Au75Si25 (off-eutectic composition) at temperatures from room temperature to 900 °C in both solid and liquid states to observe such concentration fluctuations directly. It is surprising that large SANS signals are observed in the liquids. This indicates that there are concentration fluctuations in the liquids. The concentration fluctuations are characterized by either the correlation lengths in multiple length scales or surface fractals. This finding yields new insight into the mixing state in the eutectic liquids. The mechanism of the anomalous melting point depression is discussed based on the concentration fluctuations.

Possible origin of HADES data on proton number fluctuations in Au+Au collisions

Recent data of the HADES Collaboration in Au+Au central collisions at sNN=2.4 GeV indicate large proton number fluctuations inside one unit of rapidity around midrapidity. This can be a signature of critical phenomena due to the strong attractive interactions between baryons. We study an alternative hypothesis that these large fluctuations are caused by the event-by-event fluctuations of the number of bare protons, and no interactions between these protons are assumed. The proton number fluctuations in five symmetric rapidity intervals Δy inside the region ΔY=1 are calculated using the binomial acceptance procedure. This procedure assumes the independent (uncorrelated) emission of protons, and it appears to be in agreement with the HADES data. To check this simple picture we suggest to calculate the correlation between proton multiplicities in non-overlapping rapidity intervals Δy1 and Δy2 placed inside ΔY=1.

Performance of the MPD Detector in the Study of Strangeness Production and Event-by-Event Fluctuations in Au + Au Collisions at NICA

Performance of the MPD Detector in the Study of Strangeness Production and Event-by-Event Fluctuations in Au + Au Collisions at NICA

Dynamical particle ratio fluctuations in Au + Au interaction at E lab = 30 A GeV using transport models

We present a simulation study on the dynamical fluctuations of conserved charges in a baryon-rich environment that is expected to be created in high-energy nucleus–nucleus (AB) collisions. Microscopic transport models like the ultra-relativistic quantum molecular dynamics and a multi-phase transport model are used to generate Au + Au collision events at an incident beam energy of 30 A GeV in the laboratory system. We investigate the centrality and rapidity window size dependence of the event-by-event (e-by-e) fluctuations of the multiplicity ratios of particles belonging to different species. It is observed that e-by-e dynamical fluctuations in the K/π, K/p and π/p ratios diminish with increasing centrality. Our results in this regard indicate that an AB collision can not be viewed as a mere superposition of many incoherent nucleon–nucleon (NN) collisions. Similarly, due to diffusion process the dynamical fluctuations get diluted with increasing window size of rapidity. The simulation results in general could be interpreted in terms of conventional mechanisms of particle production like resonance decays. Our simulation based analysis provides a useful reference baseline to the compressed baryonic matter experiment to be held at the Facility for Antiproton and Ion Research (FAIR).

Higher Order Moments of Proton Number Fluctuations in Au+Au Collisions at 1.23 AGeV studied with HADES

The HADES (High Acceptance DiElectron Spectrometer) experiment at the SIS18 accelerator of the GSI Helmholtzzentrum für Schwerionenforschung investigates heavy-ion collisions at kinetic beam energies of a few GeV per nucleon. We have carried out a detailed moment analysis of (net-)proton distributions of Au+Au collisions with 1.23A GeV (). We present here the correction techniques used in this investigation.

Initial-state geometry and fluctuations in Au + Au, Cu + Au, and U + U collisions at energies available at the BNL Relativistic Heavy Ion Collider

We study within the IP-Glasma and two-component MC-Glauber models the effects of initial-state geometry and fluctuations on multiplicities and eccentricities for several collision species at the Relativistic Heavy Ion Collider (RHIC). These include copper-gold (Cu + Au), gold-gold (Au + Au), and uranium-uranium (U + U) collisions. The multiplicity densities per participant pair are very similar in all systems studied. Ellipticities vary strongly between collision systems, most significantly for central collisions, while fluctuation driven odd moments vary little between systems. Event-by-event distributions of eccentricities in mid-central collisions are wider in Cu + Au relative to Au + Au and U + U systems. An anticorrelation between multiplicity and eccentricity is observed in ultracentral U + U collisions which is weaker in the IP-Glasma model than the two-component MC-Glauber model. In ultracentral Au + Au collisions the two models predict opposite signs for the slope of this correlation. Measurements of elliptic flow as a function of multiplicity in such central events can therefore be used to discriminate between models with qualitatively different particle production mechanisms.

Searching for the QCD critical point using particle ratio fluctuations and higher moments of multiplicity distributions

Dynamical fluctuations in global conserved quantities such as baryon number, strangeness or charge may be observed near a QCD critical point. Results from new measurements of dynamical K/π, p/π and K/p ratio fluctuations are presented. The commencing of a QCD critical point search at the RHIC has extended the reach of possible measurements of dynamical K/π, p/π and K/p ratio fluctuations from Au+Au collisions to lower energies. The STAR experiment has performed a comprehensive study of the energy dependence of these dynamical fluctuations in Au+Au collisions at the energies = 7.7, 11.5, 39, 62.4 and 200 GeV. New results are compared to previous measurements and to theoretical predictions from several models. The measured dynamical K/π fluctuations are found to be independent of collision energy, while dynamical p/π and K/p fluctuations have a negative value that increases toward zero at top RHIC energy. Fluctuations of the higher moments of conserved quantities (net-proton and net-charge) distributions, which are predicted to be sensitive to the presence of a critical point, are also presented.

A Study of the QCD Critical Point Using Particle Ratio Fluctuations

Dynamical fluctuations in global conserved quantities such as baryon number, strangeness, or charge may be observed near a QCD critical point. Results from new measurements of dynamical K/π and p/π ratio fluctuations are presented. The commencing of a QCD critical point search at RHIC has extended the reach of possible measurements of dynamical K/π and p/π ratio fluctuations from Au+Au collisions to lower energies. The STAR experiment has performed a comprehensive study of the energy dependence of these dynamical fluctuations in Au+Au collisions at the energies = 7.7, 11.5, and 39 GeV. New results are compared to previous measurements and to theoretical predictions from several models.

Probing freeze-out conditions in heavy ion collisions with moments of charge fluctuations

We calculate the first four moments of baryon number, electric charge and strangeness fluctuations within the hadron resonance gas model. Different moments and their ratios as well as skewness and kurtosis are evaluated on the phenomenologically determined freeze-out curve in the temperature, baryon chemical potential plane. The model results and its predictions as well as relations between different moments are compared with the first data on net proton fluctuations in Au–Au collisions obtained at RHIC by the STAR Collaboration. We find good agreement between the model calculations and experimental results. We also point out that higher order moments should be more sensitive to critical behavior and will also distinguish hadron resonance gas model calculations from results obtained from lattice QCD.

Non-flow correlations and elliptic flow fluctuations inAu+Aucollisions atsNN=200GeV

This paper presents results on event-by-event elliptic flow fluctuations in Au+Au collisions at sqrt(s_NN)=200Gev, where the contribution from non-flow correlations has been subtracted. An analysis method is introduced to measure non-flow correlations, relying on the assumption that non-flow correlations are most prominent at short ranges (Delta eta < 2). Assuming that non-flow correlations are of the order that is observed in p+p collisions for long range correlations (Delta eta > 2), relative elliptic flow fluctuations of approximately 30-40% are observed. These results are consistent with predictions based on spatial fluctuations of the participating nucleons in the initial nuclear overlap region. It is found that the long range non-flow correlations in Au+Au collisions would have to be more than an order of magnitude stronger compared to the p+p data to lead to the observed azimuthal anisotropy fluctuations with no intrinsic elliptic flow fluctuations.

Forward-backward multiplicity fluctuations in heavy nuclei collisions in the wounded nucleon model

We use the wounded nucleon model to study the forward-backward multiplicity fluctuations measured by the PHOBOS Collaboration in Au+Au collisions at sqrt(s_NN)=200 GeV. The enhancement of forward-backward fluctuations in Au+Au collisions with respect to the elementary p+p interactions is in this model explained by the asymmetric shape of the pseudorapidity density of produced particles from a single wounded nucleon and the fluctuations of the number of wounded nucleons in the colliding nuclei. The wounded nucleon model describes these experimental data better than the HIJING, AMPT or UrQMD models do.

Beam-energy and system-size dependence of dynamical net charge fluctuations

We present measurements of net charge fluctuations in Au+Au collisions at s(NN)=19.6, 62.4, 130, and 200 GeV, Cu+Cu collisions at s(NN)=62.4 and 200 GeV, and p+p collisions at s=200 GeV using the dynamical net charge fluctuations measure nu(+-,dyn). We observe that the dynamical fluctuations are nonzero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate 1/N(ch) scaling but display approximate 1/N(part) scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation.

Non-flow correlations and elliptic flow fluctuations in Au + Au collisions at GeV

We present first results on event-by-event elliptic flow fluctuations in nucleus–nucleus collisions corrected for effects of non-flow correlations where the magnitude of non-flow correlations has been independently measured in data. Over the measured range in centrality, we see large relative fluctuations of 25–50%. The results are consistent with predictions from both color glass condensate and Glauber type initial condition calculations of the event-by-event participant eccentricity fluctuations.

Elliptic flow fluctuations in Au+Au collisions at GeV

In this talk, we report an analysis of elliptic flow (v2), non-flow (δ2) and v2 fluctuations for the STAR Collaboration at middle rapidity in GeV Au+Au collisions. We compare the results to models of the fluctuations in the initial eccentricity of the overlap zone.

NeXSPheRIO results on elliptic-flow fluctuations at RHIC

By using the NeXSPheRIO code, we study the elliptic-flow fluctuations in Au + Au collisions at 200 A GeV. It is shown that, by fixing the parameters of the model to correctly reproduce the charged pseudorapidity and the transverse-momentum distributions, reasonable agreement of 〈v 2〉 with data is obtained, both as function of pseudorapidity as well as of transverse momentum, for charged particles. Our results on elliptic-flow fluctuations are in good agreement with the recently measured data on experiments.

Multiplicity fluctuations in Au+Au collisions at ultrarelativistic energies

The preliminary data of the PHENIX collaboration for the scaled variances of charged hadron multiplicity fluctuations in Au+Au at {radical}(s)=200 GeV are analyzed within the model of independent sources. We use the Hadron-String-Dynamics (HSD) transport model to calculate the participant number fluctuations and the number of charged hadrons per nucleon participant in different centrality bins. This combined picture leads to a good agreement with the PHENIX data and suggests that the measured multiplicity fluctuations result dominantly from participant number fluctuations. The role of centrality selection and acceptance is discussed separately.

Elliptic flow fluctuations in collisions at RHIC

We present first results on event-by-event elliptic flow fluctuations in Au+Au collisions at obtained with the PHOBOS detector. Over the measured range in centrality, large relative fluctuations of 40–50% are found. The elliptic flow fluctuations are well described as being proportional to fluctuations in the shape of the initial collision region, as estimated event by event with the participant eccentricity using Glauber Monte Carlo.

Elliptic flow fluctuations in Au+Au collisions at

We report first measurements of elliptic flow (v2) fluctuations for the STAR collaboration at middle rapidity in collisions. We analyse the multiplicity dependence of the flow vector length distribution to disentangle non-flow correlations from v2 fluctuations. We find that the width of the v2 distribution is approximately 36% of the mean v2 and, within errors, independent of collision centrality. This value coincides with eccentricity fluctuations, apparently leaving little room for other sources of fluctuations.