arXiv subjects

Thorsten Renk

Publications and source records attributed to Thorsten Renk.

106 records · Page 6Linked to original sources

arXiv2005

Rapidity dependence of HBT correlation radii in non-boost invariant models

Hanbury-Brown Twiss (HBT) correlation measurements provide valuable information about the phase space distribution of matter in ultrarelativistic heavy-ion collisions. The rapidity dependence of HBT radii arises from a nontrivial interplay between longitudinal and transverse expansion and the time dependence of the freeze-out pattern. For a non-accelerating longitudinal expansion the dependence primarily arises from the amount of radiating matter per unit rapidity $dN/dη$, but for a scenario with strong longitudinal acceleration additional complications occur. In this paper I explore schematically what type of dependence can be expected for RHIC conditions under different model assumptions for the dynamics of spacetime expansion and freeze-out.

hep-ph↗

arXiv2005

Flow dependence of high $p_T$ parton energy loss in heavy-ion collisions

The measured transverse momentum spectra and HBT correlations of bulk (i.e. low $p_T$) matter can be well explained by assuming that the soft sector of particles produced in ultrarelativistic heavy-ion collisions is (approximately) thermalized and undergoes collective accelerated expansion in both longitudinal and transverse direction. However, this implies that bulk matter will have a non-vanishing flow component transverse to the trajectory of a high $p_T$ partonic jets. In general, this will increase the energy loss experienced by the jet parton and modify the shape of the jet cone. In this paper, we present a systematic study of the magnitude of the additional energy loss induced by flow under realistic assumptions for the medium evolution. We argue that a perturbative QGP description may be sufficient for the measured $R_{AA}$ if flow during the medium evolution is taken into account properly.

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arXiv2005

Non-perturbative finite $T$ broadening of the $ρ$ meson and dilepton emission in heavy ion-collisions

We study self-consistently the finite $T$ broadening of the $ρ$-meson and its implications for dilepton emission in heavy ion-collisions. For this purpose finite width effects at finite temperature due to the $ρ$-$π$ interaction are investigated in a self-consistent $Φ$-functional approach. The temperature dependence of the $ρ$-meson and pion spectral functions and self-energies is discussed. The spectral functions show considerable broadening in comparison with a perturbative calculation on the one-loop level. Using these spectral functions, we make a comparison to dilepton emission data from the CERES NA49 collaboration employing a parametrized fireball evolution model of collision. We demonstrate that these non-perturbative finite width effects are in-medium modifications relevant to the understanding of the enhancement of the low invariant mass spectrum of dileptons emitted in A-A collisions.

nucl-th↗

arXiv2005

Photonic measurements of the longitudinal expansion dynamics in Heavy-Ion collisions

Due to the smallness of the electromagnetic coupling, photons escape from the hot and dense matter created in an heavy-ion collision at all times, in contrast to hadrons which are predominantly emitted in the final freeze-out phase of the evolving system. Thus, the thermal photon yield carries an imprint from the early evolution. We suggest how this fact can be used to gain information about where between the two limiting cases of Bjorken (boost-invariant expansion) and Landau (complete initial stopping and re-expansion) hydrodynamics the actual evolution can be found. We argue that both the rapidity dependence of the photon yield and photonic HBT radii are capable of answering this question.

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arXiv2004

A global description of heavy-ion collisions

A model for the evolution of ultrarelativistic heavy-ion collisions at both CERN SPS and RHIC top energies is presented. Based on the assumption of thermalization and a parametrization of the space-time expansion of the produced matter, this model is able to describe a large set of observables including hadronic momentum spectra, correlations and abundancies, the emission of real photons, dilepton radiation and the suppression pattern of charmonia. Each of these obervables provides unique capabilities to study the reaction dynamics and taken together they form a strong and consistent picture of the evolving system. Based on the emission of hard photons measured at SPS, we argue that a strongly interacting, hot and dense system with temperatures above 250 MeV has to be created early in the reaction. Such a system is bound to be different from hadronic matter and likely to be a quark-gluon plasma, and we find that this assumption is in line with the subsequent evolution of the system that is reflected in other observables.

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arXiv2004

Thermal photon spectra and HBT correlations at full RHIC energy

Using a model for the evolution of the fireball created in Au-Au collisions at full RHIC energy which reproduces the hadronic single particle spectra and two-particle correlations we calculate thermal photon emission from the hot partonic and hadronic matter. We present predictions for both the emitted photon transverse momentum spectrum and Hanbury-Brown Twiss (HBT) correlations. Surprisingly, we find that due to the strong transverse flow in the model photon emission from hadronic matter is sizeable in the momentum range expected to be dominated by thermal emission and that consequently the HBT radius parameters do not reflect exclusively properties of the partonic evolution phase. We compare to another model calculation where pre-equilibrium photon emission is dominant to illustrate the differences of both approaches.

hep-ph↗

arXiv2004

A comprehensive description of multiple observables in heavy-ion collisions at SPS

Combining and expanding on work from previous publications, a model for the evolution of ultrarelativistic heavy-ion collisions at the CERN SPS for 158 AGeV beam energy is presented. Based on the assumption of thermalization and a parametrization of the space-time expansion of the produced matter, this model is able to describe a large set of observables including hadronic momentum spectra, correlations and abundancies, the emission of real photons, dilepton radiation and the suppression pattern of charmonia. Each of these obervables provides unique capabilities to study the reaction dynamics and taken together they form a strong and consistent picture of the evolving system. Based on the emission of hard photons, we argue that a strongly interacting, hot and dense system with temperatures above 250 MeV has to be created early in the reaction. Such a system is bound to be different from hadronic matter and likely to be a quark-gluon plasma, and we find that this assumption is in line with the subsequent evolution of the system that is reflected in other observables.

hep-ph↗

arXiv2004

Why the HBT data are not in agreement with a single chemical and kinetic freeze-out

Based on simple scale arguments we argue that any thermalized fireball evolution scenario which is in agreement with the observed Hanbury-Brown Twiss (HBT) correlation radii at RHIC and reproduces the measured total multiplicity cannot reflect the distribution of matter at or close to a phase transition temperature of ~170 MeV and any scenario which assumes that HBT reflects these properties cannot be reached by a sensible choice of evolution parameters while agreeing with all correlation radii. We investigate this question in more detail using a parametrized version of the fireball evolution which has been shown to reproduce particle spectra and HBT for a separate chemical and kinetic freeze-out.

hep-ph↗

arXiv2004

A model for the spacetime evolution of heavy-ion collisions at RHIC

We investigate the space-time evolution of ultrarelativistic Au-Au collisions at full RHIC energy using a schematic model of the expansion. Assuming a thermally equilibrated system, we can adjust the essential scale parameters of this model such that the measured transverse momentum spectra and Hanbury-Brown Twiss (HBT) correlation parameters are well described. We find that the experimental data strongly constrain the dynamics of the evolution of the emission source although hadronic observables for the most part reflect the final breakup of the system.

hep-ph↗

arXiv2004

Dilepton emission rates from hot hadronic matter

The vacuum polarisation effects from the nucleon sector lead to large medium modifications of the vector meson masses in the Walecka model. With a quantum hadrodynamic framework including the quantum effects, and using a quasiparticle description for quark gluon plasma(QGP), the dilepton emission rate from the hot and dense matter resulting from relativistic nuclear collisions is calculated. Using a model for the fireball evolution which has been shown to reproduce other observables such as charmonium suppression, photon emission and the abundance of hadronic species, we compare with the dilepton invariant mass spectrum measured by the CERES collaboration at CERN SPS. We also compare the results to a previous calculation where the spectral function of a virtual photon (a key ingredient for the emission rate) has been calculated in a chiral SU(3) model.

nucl-th↗

arXiv2004

Why a long-lived fireball can be compatible with HBT measurements

The common interpretation of HBT data measured at top SPS energies leads to apparent source lifetimes of 6-8 fm/c and emission duration of approximately 2-3 fm/c. We investigate a scenario with continuous pion emission from a long-lived (~17 fm/c) thermalized source in order to show that it is not excluded by the data. Starting from a description of the source's spacetime expansion based on gross thermodynamical properties of hot matter (which is able to describe a number of experimental observables), we introduce the pion emission function with a contribution from continuous emission during the source's lifetime and another contribution from the final breakup and proceed by calculating the HBT parameters R_out and R_side. The results are compared with experimental data measured at SPS for 158 AGeV central Pb-Pb collisions. We achieve agreement with data, provided that some minor modifications of the fireball evolution scenario are made and find that the parameter R_out is not sensitive to the fireball lifetime, but only to the duration of the final breakup, in spite of the fact that emission takes place throughout the whole lifetime. We explicitly demonstrate that those findings do not alter previous results obtained within this model.

hep-ph↗

arXiv2003

Statistical Hadronization as a Snapshot of a dynamical Fireball Evolution

Statistical hadronization models are extremly succesful in describing measured ratios of hadrons produced in heavy-ion collisions for a wide range of beam energies from SIS to RHIC. Using the idea of statistical hadronization at the phase boundary within the framework of a recently proposed dynamical model for the thermodynamics of fireballs, we establish a relation between the equation of state (EoS) in the partonic phase probed at the phase transition temperature T_C and the measured hadron ratios. In this way, the ratios can be predicted parameter-free. We demonstrate that this framework gives a consistent description of conditions both at SPS and RHIC. As the data on dilepton emission from heavy ion collisions give evidence for strong in-medium modifications of hadronic properties, we schematically investigate the sensitivity of our results to such modifications and qualitatively sketch a consistent scenario involving such in-medium effects.

hep-ph↗

arXiv2003

Kinetic description of charmonium production in high-energy nuclear collisions

We study the evolution of charmonia as they collide with the constituents of the fireball produced in high-energy nucleus-nucleus collisions. The latter evolves in a manner controlled by the equation of state as given by lattice QCD, and is constructed in such a way that the observed hadronic spectra are correctly reproduced. A kinetic description of charmonium interactions with both quark-gluon and hadronic degrees of freedom allows to study in detail the evolution in different regimes, controlled by collision energy, kinematics and geometry. The data collected at the CERN-SPS accelerator are well described and new estimates for J/psi production at BNL-RHIC are presented.

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arXiv2003

Emission of thermal photons and the equilibration time in Heavy-Ion collisions

The emission of hard real photons from thermalized expanding hadronic matter is dominated by the initial high-temperature expansion phase. Therefore, a measurement of photon emission in ultrarelativistic heavy-ion collisions provides valuable insights into the early conditions realized in such a collision. In particular, the initial temperature of the expanding fireball or equivalently the equilibration time of the strongly interacting matter are of great interest. An accurate determination of these quantities could help to answer the question whether or not partonic matter (the quark gluon plasma) is created in such collisions. In this work, we investigate the emission of real photons using a model which is based on the thermodynamics of QCD matter and which has been shown to reproduce a large variety of other observables. With the fireball evolution fixed beforehand, we are able to extract limits for the equilibration time by a comparison with photon emission data measured by WA98.

hep-ph↗

arXiv2001

Note on the Impact Parameter Analysis of High Energy Proton Proton Collisions

Following prior analysis for measured pp elastic differential cross section, the impact parameter representation in terms of profile functions is calculated from two different parameterizations on single diffractive dissociation data. The derivative of this quantity with respect to the collision energy squared s measures the growth rate of the reaction's blackness. Its distribution in impact parameter space allows detailed insight into the growth pattern of the total cross section and the approaching unitarity limit. Comparing the results with the elastic case, the different mechanisms of unitarization of the two parametrizations are discussed.

hep-ph↗

arXiv2000

Coordinate Space Distributions of Antiquark Flavor Asymmetries in the Proton

We examine the space-time properties of the distribution (dbar - ubar) and dbar/ubar in the proton. The difference of the antiquark distributions shows the expected peak at the approximate pion Compton wavelength and is supportative of the thesis that the meson cloud of the nucleon is at the origin of the asymmetry of (dbar - ubar), with the pion cloud playing a dominant role.

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