Dynamical Net Charge Fluctuations Research Articles

System size dependence of net-charge fluctuation in nucleus-nucleus collisions at FAIR energies

Dynamical net-charge fluctuations are studied in symmetric nuclear collisions of different system size and at two different collision energies that in the near future will be available at the Facility for Antiproton and Ion Research (FAIR). Multiparticle emission data simulated by the ultra-relativistic quantum molecular dynamics (UrQMD) are analyzed for this purpose. Our primary objective is to examine the system size dependence of dynamical fluctuation of conserved charge at typical FAIR conditions. The centrality, pseudorapidity interval size and azimuthal angle interval size dependence of the dynamical fluctuations are studied too. The effects of global charge conservation (GCC) and finite multiplicity bin width correction are taken into account. To a large extent the systematics followed by the dynamical fluctuations at FAIR conditions are found to be a lower energy extrapolation of the observations made in this regard in the Relativistic Heavy-ion Collider (RHIC) experiments.

Contributions of Jets in Net Charge Fluctuations from the Beam Energy Scan at RHIC and LHC

Dynamical net charge fluctuations have been studied in ultrarelativistic heavy-ion collisions from the beam energy scan at RHIC and LHC energies by carrying out the hadronic model simulation. Monte Carlo model, HIJING, is used to generate events in two different modes, HIJING-default with jet quenching switched off and jet/minijet production switched off. A popular variable, ν[+-,dyn], is used to study the net charge fluctuations in different centrality bins and the findings are compared with the available experimental values reported earlier. Although the broad features of net charge fluctuations are reproduced by the HIJING, the model predicts the larger magnitude of fluctuations as compared to the one observed in experiments. The role of jets/minijets production in reducing the net charge fluctuations is, however, distinctly visible from the analysis of the two types of HIJING events. Furthermore, dNch/dη and 1/N scaling is partially exhibited, which is due to the fact that, in HIJING, nucleus-nucleus collisions are treated as multiple independent nucleon-nucleon collisions.

Isolating dynamical net-charge fluctuations

We modify the usual definitions of cumulants of net-charge fluctuations in a way that isolates dynamical fluctuations. The new observables, which we call dynamical cumulants, are robust with respect to trivial correlations induced by volume fluctuations and global charge conservation. We illustrate the potential of dynamical cumulants by carrying out Monte Carlo simulations where all correlations are trivial. The results of our simulations agree well with Relativistic Heavy Ion Collider (RHIC) data, and are used to illustrate that dynamical cumulants consistently isolate dynamical fluctuations.

On Dynamical Net-Charge Fluctuations within a Hadron Resonance Gas Approach

The dynamical net-charge fluctuations (νdyn) in different particle ratiosK/π,K/p, andp/πare calculated from the hadron resonance gas (HRG) model and compared with STAR central Au+Au collisions atsNN=7.7–200 GeV and NA49 central Pb+Pb collisions atsNN=6.3–17.3 GeV. The three charged particle ratios (K/π,K/p, andp/π) are determined as total and average of opposite and average of the same charges. We find an excellent agreement between the HRG calculations and the experimental measurements, especially from STAR beam energy scan (BES) program, while the strange particles in the NA49 experiment at lower Super Proton Synchrotron (SPS) energies are not reproduced by the HRG approach. We conclude that the utilized HRG version seems to take into consideration various types of correlations including strong interactions through the heavy resonances and their decays especially at BES energies.

Charged-to-neutral correlation at forward rapidity in Au + Au collisions atsNN=200GeV

Event-by-event fluctuations of the ratio of inclusive charged to photon multiplicities at forward rapidity in Au+Au collision at $\sqrt{s_{NN}}$=200 GeV have been studied. Dominant contribution to such fluctuations is expected to come from correlated production of charged and neutral pions. We search for evidences of dynamical fluctuations of different physical origins. Observables constructed out of moments of multiplicities are used as measures of fluctuations. Mixed events and model calculations are used as baselines. Results are compared to the dynamical net-charge fluctuations measured in the same acceptance. A non-zero statistically significant signal of dynamical fluctuations is observed in excess to the model prediction when charged particles and photons are measured in the same acceptance. We find that, unlike dynamical net-charge fluctuation, charge-neutral fluctuation is not dominated by correlation due to particle decay. Results are compared to the expectations based on the generic production mechanism of pions due to isospin symmetry, for which no significant (<1%) deviation is observed.

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

We present measurements of net charge fluctuations in $Au + Au$ collisions at $\sqrt{s_{NN}} = $ 19.6, 62.4, 130, and 200 GeV, $Cu + Cu$ collisions at $\sqrt{s_{NN}} = $ 62.4, 200 GeV, and $p + p$ collisions at $\sqrt{s} = $ 200 GeV using the net charge dynamical fluctuations measure $\nu_{+-,dyn}$. The dynamical fluctuations are non-zero at all energies and exhibit a rather modest dependence on beam energy. We find that at a given energy and collision system, net charge dynamical fluctuations violate $1/N_{ch}$ scaling, but display approximate $1/N_{part}$ scaling. We observe strong dependence of dynamical fluctuations on the azimuthal angular range and pseudorapidity widths.

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.

Net Charge Fluctuations at RHIC

We present measurements of dynamical net charge fluctuations in Au+Au collisions at $$\sqrt {s_{NN} } = 20$$ , 62, 130 and 200 GeV using the measure ν +−,dyn. We observe the dynamical fluctuations are finite at all energies, and do not exhibit dependence on beam energy. We find net charge fluctuations violate the trivial 1/N scaling expected for nuclear collisions consisting of independent nucleon-nucleon interactions. We also find dynamical fluctuations exhibit sizable dependence of the pseudo-rapidity and azimuthal ranges of integration. We compare measured data with transport models and a toy model invoking radial flow, and show the bulk of the measured correlations can be accounted for by resonance production and radial collective flow.

Event-by-Event Net Charge Fluctuations

We present analyses of event-by-event dynamical net charge fluctuations measured in 130 and 200 GeV Au Au collisions with the STAR detector. The dynamical net charge fluctuations are evaluated using the $\nu_{+-,dyn}$ observable. Dynamical fluctuations measured in Au Au collisions at 130 and 200 GeV are finite, and exceed charge conservation limits. They deviate from a perfect 1/N scaling and provide an indication that the collision dynamics varies with collision centrality.

Event-by-event fluctuations at 40, 80 and 158 A GeV/c in Pb + Au collisions

Event-by-event fluctuations of mean pT and net charge in 40, 80 and 158 A GeV/c Pb+Au collisions are presented. The observed dynamical mean pT fluctuations in central events of about 1% are very similar to results from RHIC. The centrality dependence of mean pT fluctuations at 158 A GeV/c shows a peculiar non-monotonic pattern with respect to the extrapolation from the fluctuations measured in p+p collisions. Dynamical net charge fluctuations smaller than the charge conservation limit are observed. After correction for charge conservation, the measured fluctuation signal in central events is comparable to RHIC results.

Net charge dynamic fluctuations

We define and discuss the properties of the dynamical net charge fluctuations, ν +−, dyn , for measurements of net charge (conserved quantities) fluctuations. The dynamical fluctuations are related to integrals of single- and two-particle densities. They are robust observables, i.e. nearly independent of detection efficiencies. Scaling properties with colliding system size and relationships to other observables are also discussed.