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Joerg Aichelin

Publications and source records attributed to Joerg Aichelin.

68 records · Page 4Linked to original sources
arXiv2012

Radiative energy loss in the absorptive QGP: taming the long formation lengths in coherent emission

In an absorptive plasma, damping of radiation mechanisms can influence the bremsstrahlung formation in case of large radiation formation lengths. We study qualitatively the influence of this effect on the gluon bremsstrahlung spectrum off heavy quarks in the quark-gluon plasma. Independent of the heavy-quark mass, the spectrum is found to be strongly suppressed in an intermediate gluon energy region which grows with increasing gluon damping rate and increasing energy of the heavy quark. Thus, just as polarization effects in the plasma render the bremsstrahlung spectra independent of the quark mass in the soft gluon regime, damping effects tend to have a similar impact for larger gluon energies.

hep-ph↗
arXiv2012

Recent results on heavy quark quenching in ultrarelativistic heavy ion collisions

In this contribution, we present some predictions for the production of D and B mesons in ultrarelativistic heavy ion collisions at RHIC and LHC energies and confront them with experimental results obtained so far by the STAR, PHENIX, ALICE and CMS collaborations. We next discuss some preliminary results obtained with an improved description of the medium based on EPOS initial conditions, and its possible implications on the nuclear modification factor and on the elliptic flow of heavy quarks.

hep-ph↗
arXiv2012

Theory of heavy quark energy loss

We briefly review some of the models and theoretical schemes established to describe heavy quark quenching in ultrarelativistic heavy ions collisions. Some lessons are derived from RHIC and early LHC data, especially as for the contraints they impose on those models.

hep-ph↗
arXiv2012

Radiative energy loss reduction in an absorptive plasma

The influence of the damping of radiation on the radiative energy loss spectrum of a relativistic charge in an infinite, absorptive plasma is studied. We find increasing reduction of the spectrum with increasing damping. Our studies, which represent an Abelian approximation for the colour charge dynamics in the quark-gluon plasma, may influence the analysis of jet quenching phenomena observed in high-energy nuclear collisions. Here, we focus on a formal discussion of the limiting behaviour with increasing radiation frequency. In an absorptive (and polarizable) medium, this is determined by the behaviour of the exponential damping factor entering the spectrum and the formation time of radiation.

hep-ph↗
arXiv2011

Heavy Quark Energy Loss in High Multiplicity Proton Proton Collisions at LHC

One of the most promising probes to study deconfined matter created in high energy nuclear collisions is the energy loss of (heavy) quarks. It has been shown in experiments at the Relativistic Heavy Ion Collider (RHIC) that even charm and bottom quarks, despite their high mass, experience a remarkable medium suppression in the Quark Gluon Plasma. In this exploratory investigation we study the energy loss of heavy quarks in high multiplicity proton-proton collisions at LHC energies. Although the colliding systems are smaller than compared to those at RHIC (p+p vs. Au+Au) the higher energy might lead to multiplicities comparable to Cu+Cu collisions at RHIC. Recently the CMS collaboration has shown that these particles likely interact among each other. The interaction of charm quarks with this environment gives rise to a non-negligible suppression of high momentum heavy quarks in elementary collisions.

hep-ph↗
arXiv2011

The influence of bulk evolution models on heavy-quark phenomenology

We study the impact of different Quark-Gluon Plasma expansion scenarios in heavy-ion collisions on spectra and elliptic flow of heavy quarks. For identical heavy-quark transport coefficients relativistic Langevin simulations with different expansion scenarios can lead to appreciable variations in the calculated suppression and elliptic flow of the heavy-quark spectra, by up to a factor of two. A cross comparison with two sets of transport coefficients supports these findings, illustrating the importance of realistic expansion models for quantitative evaluations of heavy-quark observables in heavy-ion collisions. It also turns out that differences in freeze-out prescriptions and Langevin realizations play a significant role in these variations. Light-quark observables are essential in reducing the uncertainties associated with the bulk-matter evolution, even though uncertainties due to the freeze-out prescription persist.

hep-ph↗
arXiv2010

Resonances as a possible observable of hot and dense nuclear matter

One of the most fundamental questions in the field of relativistic heavy ion physics is how to reach and explore densities which are needed to cross the chiral and/or the deconfinement phase transition. In this analysis we investigate the information we can gather by analyzing baryonic and mesonic resonances on the hot and dense phase in such nuclear reactions. The decay products of these resonances carry information on the resonances properties at the space time point of their decay. We especially investigate the percentage of reconstructable resonances as a function of density for heavy ion collisions in the energy range between $E_{lab}$ = 30 AGeV and $\sqrt{s}$ = 200 AGeV, the energy domain between the future FAIR facility and the present RHIC collider.

nucl-th↗
arXiv2009

Energy Loss of Heavy Quarks in a QGP with a Running Coupling Constant Approach

We show that the effective running coupling constant, $α_{\rm eff}$, and the effective regulator, $κ\tilde{m}_{D}^2$, which we used recently to calculate the energy loss, $\frac{dE}{dx}$, and the elliptic flow, $v_2$, of heavy quarks in an expanding quark gluon plasma plasma (QGP) are compatible with lattice results and with recently advanced analytical pQCD calculation.

hep-ph↗
arXiv2005

Hadronic Matter is Soft

The stiffness of the hadronic equation of state has been extracted from the production rate of $K^+$ mesons in heavy ion collisions around 1 $A$ GeV incident energy. The data are best described with a compressibility coefficient $κ$ around 200 MeV, a value which is usually called ``soft''. This is concluded from a detailed comparison of the results of transport theories with the experimental data using two different procedures: (i) the energy dependence of the ratio of $K^+$ from Au+Au and C+C collisions and (ii) the centrality dependence of the $K^+$ multiplicities. It is demonstrated that input quantities of these transport theories which are not precisely known, like the kaon-nucleon potential, the $ΔN \to N K^+ Λ$ cross section or the life time of the $Δ$ in matter do not modify this conclusion.

nucl-th↗
arXiv2001

Strangeness Suppression in Proton-Proton Collisions

We analyse strangeness production in proton-proton (pp) collisions at SPS and RHIC energies, using the recently advanced NeXus approach. After having verified that the model reproduces well the existing data, we interpret the results: strangeness is suppressed in proton-proton collisions at SPS energy as compared to electron-positron (e+e-) annihilation due to the limited masses of the strings produced in the reaction, whereas high energy pp and e+e- collisions agree quantitatively . Thus strangeness suppression at SPS energies is a consequence of the limited phase-space available in string fragmentation.

hep-ph↗
arXiv1998

Simulated Annealing Clusterization Algorithm for Studying the Multifragmentation

We present the details of the numerical realization of the recently advanced algorithm developed to identify the fragmentation in heavy ion reactions. This new algorithm is based on the Simulated Annealing method and is dubbed as Simulated Annealing Clusterization Algorithm [SACA]. We discuss the different parameters used in the Simulated Annealing method and present an economical set of the parameters which is based on the extensive analysis carried out for the central and peripheral collisions of Au-Au, Nb-Nb and Pb-Pb. These parameters are crucial for the success of the algorithm. Our set of optimized parameters gives the same results as the most conservative choice, but is very fast. We also discuss the nucleon and fragment exchange processes which are very important for the energy minimization and finally present the analysis of the reaction dynamics using the new algorithm. This algorithm is can be applied whenever one wants to identify which of a given number of constituents form bound objects.

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arXiv1997

The importance of initial-final state correlations for the formation of fragments in heavy ion collisions

Using quantum molecular dynamics simulations, we investigate the formation of fragments in symmetric reactions between beam energies of E=30AMeV and 600AMeV. After a comparison with existing data we investigate some observables relevant to tackle equilibration: dsigma/dErat, the double differential cross section dsigma/pt.dpz.dpt,... Apart maybe from very energetic E>400AMeV and very central reactions, none of our simulations gives evidence that the system passes through a state of equilibrium. Later, we address the production mechanisms and find that, whatever the energy, nucleons finally entrained in a fragment exhibit strong initial-final state correlations, in coordinate as well as in momentum space. At high energy those correlations resemble the ones obtained in the participant-spectator model. At low energy the correlations are equally strong, but more complicated; they are a consequence of the Pauli blocking of the nucleon-nucleon collisions, the geometry, and the excitation energy. Studying a second set of time-dependent variables (radii, densities,...), we investigate in details how those correlations survive the reaction especially in central reactions where the nucleons have to pass through the whole system. It appears that some fragments are made of nucleons which were initially correlated, whereas others are formed by nucleons scattered during the reaction into the vicinity of a group of previously correlated nucleons.

nucl-th↗
arXiv1995

Chiral phase transition in an expanding quark antiquark plasma

We investigate the time evolution of a quark antiquark plasma by solving numerically the relativistic transport equations derived on the Hartree level from the Nambu-Jona-Lasinio model. We find that the phase transition in the expanding quark antiquark plasma is different as compared to that in a static plasma. The expansion competes with the transition and finally quark droplets will be formed which subsequently hadronizes. These findings raise the question whether static thermal models can make at all any prediction about signals of that transition .

hep-ph↗