Thermal open charm signals versus hard initial yields in ultrarelativistic heavy-ion collisions

Kämpfer, B.; Pavlenko, O. P.; Peshier, A.; Hentschel, Martina; Soff, G.

doi:10.1088/0954-3899/23/12/025

Cited by 28 publications

(28 citation statements)

References 28 publications

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“…For EOS Q we find T dec =120 MeV, e 0 =9.0 GeV/fm 3 , n 0 =0.95 fm −3 , and τ 0 =0.8 fm/c. The freeze-out temperature and the average radial flow resulting from these initial conditions agree well with previous studies [25][26][27]. In calculating the negative hadron spectrum we included [28] decays of all resonances up to the mass of the ∆(1232); resonance decays are found to reduce the momentum anisotropies v 2,4 for pions by 10-15%.…”

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confidence: 76%

Anisotropic flow from AGS to LHC energies

1999

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Within hydrodynamics we study the effects of the initial spatial anisotropy in non-central heavy-ion collisions on the momentum distributions of the emitted hadrons. We show that the elliptic flow measured at midrapidity in 158 A GeV/c Pb+Pb collisions can be quantitatively reproduced by hydrodynamic expansion, indicating early thermalization in the collision. We predict the excitation functions of the 2 nd and 4 th harmonic flow coefficients from AGS to LHC energies and discuss their sensitivity to the quark-hadron phase transition.The recent observation of transverse collective flow phenomena in non-central heavy-ion collisions at ultrarelativistic beam energies [1][2][3][4] has led to renewed intense theoretical interest in this topic (see [5] for a review). Collective flow is the consequence of pressure in the system and thereby provides access to the equation of state of the hot and dense matter ("fireball") formed in the reaction zone. This access is indirect since the flow in the final state represents a time integral over the pressure history of the fireball. Sorge [6] has argued that different types of transverse flow (radial, directed, elliptic, see [5]) show different sensitivities to the early and late stages of the collision such that a combination of flow observables may allow for a more differential investigation of the equation of state. In particular, he pointed out that the elliptic flow (which develops in non-central collisions predominantly at midrapidity and manifests itself as an elliptic deformation of the hadronic momentum distributions around the beam axis [7,8]) is a signature for the early stage of the collision: its driving force is the spatial eccentricity of the dense nuclear overlap region which, if thermalized quickly enough, leads to an anisotropy of the pressure gradients which cause the expansion. Since the developing anisotropic flow reduces the eccentricity of the fireball, it acts against its own cause and thus shuts itself off after some time. Radial flow, on the other hand, responds to the absolute magnitude of the pressure gradients and not only to their anisotropy; it therefore exists also in central collisions, and in non-central collisions it continues to grow even after the initial elliptic spatial deformation of the fireball has disappeared.A phase transition from a hadron gas to a colordeconfined quark-gluon plasma causes a softening of the * On leave of absence from Institut für Theoretische Physik, Universität Regensburg. Email: Ulrich.Heinz@cern.ch equation of state: as the temperature crosses the critical value for the phase transition, the energy and entropy densities increase rapidly while the pressure rises slowly. The resulting small ratio of p/e at the upper end of the transition region ("the softest point" [9]) weakens the build-up of flow as the system passes through it. Shuryak [10] and van Hove [11] therefore suggested that a plot of the mean transverse momentum against the central multiplicity density should show a plateau. Later hydrodynamic calculati...

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confidence: 76%

Anisotropic flow from AGS to LHC energies

1999

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“…Here we have to mention that the cut-off m T − m > 0.4 GeV has been applied in the experimental analysis, too [41]. For the Pb + Pb spectra at 160 A·GeV our freeze-out parameters are similar to those from Kämpfer [42] (T = 120 MeV, β = 0.43; star in the lower left plot). The dashed lines in the right panel of Fig.…”

Section: Reactions Of Finite Systemsmentioning

confidence: 94%

Aspects of thermal and chemical equilibration of hadronic matter

et al. 2000

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We study thermal and chemical equilibration in 'infinite' hadron matter as well as in finite size relativistic nucleus-nucleus collisions using a BUU cascade transport model that contains resonance and string degrees-of-freedom. The 'infinite' hadron matter is simulated within a cubic box with periodic boundary conditions. The various equilibration times depend on baryon density and energy density and are much shorter for particles consisting of light quarks then for particles including strangeness. For kaons and antikaons the chemical equilibration time is found to be larger than ≃ 40 fm/c for all baryon and energy densities considered. The inclusion of continuum excitations, i.e. hadron 'strings', leads to a limiting temperature of T s ≃ 150 MeV. We, furthermore, study the expansion of a hadronic fireball after equilibration. The slope parameters of the particles after expansion increase with their mass; the pions leave the fireball much faster then nucleons and accelerate subsequently heavier hadrons by rescattering ('pion wind'). If the system before expansion is close to the limiting temperature T s , the slope parameters for all particles after expansion practically do not depend on (initial) energy and baryon density. Finally, the equilibration in relativistic nucleus-nucleus collision is considered. Since the reaction time here is much shorter than the equilibration time for strangeness, a chemical equilibrium of strange particles in heavy-ion collisions is not supported by our transport calculations. However, the various particle spectra can approximately be described within the blast model.

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“…The transverse momentum spectra therefore determine the thermal freeze-out parameters. This has been done by several groups in the past few years [19][20][21][22][23][24][25][26][27] and results are shown in Fig. 4.…”

Section: Thermal Freeze-out Parametersmentioning

confidence: 99%

Chemical and thermal freeze-out parameters from1Ato200AGeV

1999

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The present knowledge about hadrons produced in relativistic heavy ion collisions is compatible with chemical freeze-out happening when the energy density divided by the particle density reaches the value of 1 GeV. This observation is used to determine the energy dependence of the chemical freeze-out parameters T ch and B ch for beam energies varying between 1 and 200A GeV. The consequences of this energy dependence are studied for various particle ratios. Predictions for particle ratios at beam energy 40A GeV are presented. The conditions for thermal freeze-out are also determined. These correspond either to an energy density of 45 MeV/fm 3 or to a particle density of 0.05/fm 3 . ͓S0556-2813͑99͒03911-4͔ PACS number͑s͒: 25.75.Dw, 12.38.Mh, 24.10.Nz, 25.75.Gz 2 2 K 2 ͑ m i /T ͒e i /T . ͑2.1͒ *On sabbatical leave at the

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Thermal open charm signals versus hard initial yields in ultrarelativistic heavy-ion collisions

Cited by 28 publications

References 28 publications

Anisotropic flow from AGS to LHC energies

Anisotropic flow from AGS to LHC energies

Aspects of thermal and chemical equilibration of hadronic matter

Chemical and thermal freeze-out parameters from1Ato200AGeV

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