We calculate second- and fourth-order cumulants of conserved charges in a temperature range stretching from the QCD transition region towards the realm of (resummed) perturbation theory. We perform ...lattice simulations with staggered quarks; the continuum extrapolation is based on N sub()t =10-24 in the crossover region and N sub()t= 8-16 at higher temperatures. We find that the hadron resonance gas model predictions describe the lattice data rather well in the confined phase. At high temperatures (above ~ 250 MeV) we find agreement with the three-loop hard thermal loop results.
Like fluctuations, nondiagonal correlators of conserved charges provide a tool for the study of chemical freeze-out in heavy ion collisions. They can be calculated in thermal equilibrium using ...lattice simulations, and be connected to moments of event-by-event net-particle multiplicity distributions. We calculate them from continuum-extrapolated lattice simulations at μB=0, and present a finite-μB extrapolation, comparing two different methods. In order to relate the grand canonical observables to the experimentally available net-particle fluctuations and correlations, we perform a hadron resonance gas model analysis, which allows us to completely break down the contributions from different hadrons. We then construct suitable hadronic proxies for fluctuation ratios, and study their behavior at finite chemical potentials. We also study the effect of introducing acceptance cuts, and argue that the small dependence of certain ratios on the latter allows for a direct comparison with lattice QCD results, provided that the same cuts are applied to all hadronic species. Finally, we perform a comparison for the constructed quantities for experimentally available measurements from the STAR Collaboration. Thus, we estimate the chemical freeze-out temperature to 165 MeV using a strangeness-related proxy. This is a rather high temperature for the use of the hadron resonance gas; thus, further lattice studies are necessary to provide first principle results at intermediate μB.
Continuum extrapolated lattice QCD calculations of quantum number specific susceptibilities and the most recent RHIC and LHC data on produced particle yields, as well as their higher moment ...fluctuations, can be interpreted using a scenario of sequential flavor dependent hadronization during the QCD crossover transition. I will present the latest data from lattice QCD and experiment and confront the question whether the separation of strangeness and light quark chemical freeze-out could have consequences beyond a simple strangeness enhancement, firstly in the production of exotic strange states and secondly in the flavor dependent evolution of dynamic quantities such as in-medium energy loss and anisotropic flow, which are generated predominantly during the collective partonic phase.
We present the crossover line between the quark gluon plasma and the hadron gas phases for small real chemical potentials. First we determine the effect of imaginary values of the chemical potential ...on the transition temperature using lattice QCD simulations. Then we use various formulas to perform an analytic continuation to real values of the baryo-chemical potential. Our data set maintains strangeness neutrality to match the conditions of heavy ion physics. The systematic errors are under control up to μB≈300 MeV. For the curvature of the transition line we find that there is an approximate agreement between values from three different observables: the chiral susceptibility, chiral condensate and strange quark susceptibility. The continuum extrapolation is based on Nt=10, 12 and 16 lattices. By combining the analysis for these three observables we find, for the curvature, the value κ=0.0149±0.0021.
We compare the mean-over-variance ratio of the net-kaon distribution calculated within a stateof-the-art hadron resonance gas model to the latest experimental data from the Beam Energy Scan at RHIC ...by the STAR collaboration. Our analysis indicates that it is not possible to reproduce the experimental results using the freeze-out parameters from the existing combined fit of net-proton and net-electric charge mean-over-variance. The strange mesons need about 10-15 MeV higher temperatures than the light hadrons at the highest collision energies. In view of the future Λ fluctuation measurements, we predict the Λ variance-over-mean and skewness-times-variance at the light and strange chemical freeze-out parameters. We observe that the Λ fluctuations are sensitive to the difference in the freeze-out temperatures established in this analysis. Our results have implications for other phenomenological models in the field of relativistic heavy ion collisions.
We study the mechanism and probability of in-medium hadronization in the deconfined medium produced in heavy-ion collisions at RHIC and LHC. We show the likelihood of color-neutral objects to be ...formed inside the partonic fireball and the probability of these states to escape the medium with reduced interaction strength and energy loss. We will suggest specific measurements that are sensitive to the early degrees of freedom and show predictions for these measurements at RHIC and the LHC.
Hadronic resonances can play a pivotal role in providing experimental evidence for partial chiral symmetry restoration in the deconfined quark–gluon phase produced at RHIC and the LHC. Their ...lifetimes, which are comparable to the lifetime of the partonic plasma phase, make them an invaluable tool to study medium modifications to the resonant state due to the chiral transition. In this Letter we show that the heavier, but still abundant, light and strange quark resonances K∗, ϕ, Δ and Λ∗ have large probability to be produced well within the plasma phase due to their short formation times. We demonstrate that, under particular kinematic conditions, these resonances can be formed and will decay inside the partonic state, but still carry sufficient momentum to not interact strongly with the hadronic medium after the QCD phase transition. Thus, K∗, ϕ, Δ and Λ∗ should exhibit the characteristic property modifications which can be attributed to chiral symmetry restoration, such as mass shifts, width broadening or branching ratio modifications.
We calculate the QCD cross-over temperature, the equation of state and fluctuations of conserved charges at finite density by analytical continuation from imaginary to real chemical potentials. Our ...calculations are based on new continuum extrapolated lattice simulations using the 4stout staggered actions with a lattice resolution up to Nt=16. The simulation parameters are tuned such that the strangeness neutrality is maintained, as it is in heavy ion collisions.
I will show recent results of the STAR experiment measured in p-p, d-Au and Au-Au collisions at RHIC energies. Evidence for collective behavior of a new phase of matter is shown based on bulk ...properties. The characterization of the new matter, using high momentum particles produced in the same collisions, indicates that partons are indeed the relevant degrees of freedom in the produced state. Surprisingly the medium exhibits strong coupling, though, and seems to behave more like an ideal fluid than a weakly interacting plasma. Unique features such as strong partonic flow and jet quenching will be discussed in detail.
We extract chemical freeze-out conditions via a thermal model approach from fluctuation observables measured at RHIC and compare with results from lattice QCD and statistical hadronization model ...fits. The possible influence of additional critical and non-critical fluctuation sources not accounted for in our analysis is discussed.
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