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Results on event-by-event fluctuations of the mean transverse momentum and net charge in Pb-Au collisions, measured by the CERES Collaboration at CERN-SPS, are presented. We discuss the centrality and beam energy dependence and compare our data to cascade calculations.
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The latest NA49 results on event-by-event transverse momentum fluctuations are presented for central Pb+Pb interactions over the whole SPS energy range (20A - 158A GeV). Two different methods are applied: evaluating the $Phi_{p_{T}}$ fluctuation measure and studying two-particle transverse momentum correlations. The obtained results are compared to predictions of the UrQMD model. The results on the energy dependence are compared to the NA49 data on the system size dependence. The NA61 (SHINE, NA49-future) strategy of searching of the QCD critical end-point is also discussed.
Event-by-event fluctuations of mean pt and net charge in 40, 80, and 158 AGeV/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 AGeV/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.
This paper presents the first measurement of event-by-event fluctuations of the elliptic flow parameter v_2 in Au+Au collisions at sqrt(s_NN) = 200GeV as a function of collision centrality. The relative non-statistical fluctuations of the v_2 parameter are found to be approximately 40%. The results, including contributions from event-by-event elliptic flow fluctuations and from azimuthal correlations that are unrelated to the reaction plane (non-flow correlations), establish an upper limit on the magnitude of underlying elliptic flow fluctuations. This limit is consistent with predictions based on spatial fluctuations of the participating nucleons in the initial nuclear overlap region. These results provide important constraints on models of the initial state and hydrodynamic evolution of relativistic heavy ion collisions.
A Monte Carlo study of identified particle ratio fluctuations at LHC energies is carried out in the frame work of hij model using the fluctuation variable $ u_{dyn}$. The simulated events for Pb-Pb collisions at $sqrt{s}_{NN}$ = 2.76 and 5.02 TeV and Xe-Xe collisions at $sqrt{s}_{NN}$ = 5.44 TeV are analyzed. From this study, it is observed that the values of $[pi,K]$, $[p,K]$ and $[pi,p]$ follow the similar trends of energy dependence as observed in the most central collision data by NA49, STAR and ALICE experiments. It is also observed that $ u_{dyn}$ for all the three combinations of particles for semi-central and central collisions, the model predicted values of $ u_{dyn}[A,B]$ for Pb-Pb collisions at $sqrt{s}_{NN}$ = 2.76 TeV agree fairly well with those observed in ALICE experiment. For peripheral collisions, however, the model predicted values of $ u_{dyn}[pi,K]$ are somewhat smaller, whereas for $[p,K]$ and $[pi,p]$ it predicts larger values as compared to the corresponding experimental values. The possible reasons for the observed differences are discussed. The $ u_{dyn}$ values scaled with charged particle density when plotted against $langle$N$_{part}$$rangle$, exhibit a flat behaviour, as expected from the independent particle emission sources. For $[p,K]$ and $[pi,p]$ combinations, a departure from the flat trend is, however, observed in central collisions in the case of low p$_{T}$ window when effect of jet quenching or resonances are considered. Furthermore, the study of $ u_{dyn}[A,B]$ dependence on particle density for various collision systems (including proton-proton collisions) suggests that at LHC energies $ u_{dyn}$ values for a given particle pair is simply a function of charged particle density, irrespective of system size, beam energy and collision centrality.
Fluctuations of thermodynamic quantities are fundamental for the study of the QGP phase transition. Among several observables calculated on an event-by-event basis, the different measures of the charge and mean transverse momentum fluctuations are of particular interest since they are considered to be indicators of the existence and of the order of this transition as well as of the thermalization in heavy--ion collisions. In this article, we review the first results from the event-by-event physics program of the ALICE experiment at the LHC in Pb--Pb collisions at $sqrt{s_{NN}} = 2.76$ TeV. The experimental results will be compared to previously published data and available model predictions.
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