arXiv subjects

Sascha Vogel

Publications and source records attributed to Sascha Vogel.

13 recordsLinked to original sources

arXiv2013

Photon Signals from Quarkyonic Matter

We calculate the Bremsstrahlung photon spectrum emitted from dynamically evolving quarkyonic matter, and compare this spectrum with that of a high chemical potential quark-gluon plasma as well as to a hadron gas. We find that the transverse momentum distribution and the harmonic coefficient is markedly different in the three cases. The transverse momentum distribution of quarkyonic matter can be fit with an exponential, but is markedly steeper than the distribution expected for the quark-gluon plasma or a hadron gas, even at the lower temperatures expected in the critical point region. The quarkyonic elliptic flow coefficient fluctuates randomly from event to event, and within the same event at different transverse momenta. The latter effect, which can be explained by the shape of quark wavefunctions within quarkyonic matter, might be considered as a quarkyonic matter signature, provided initial temperature is low enough that the quarkyonic regime dominates over deconfinement effects, and the reaction-plane flow can be separated from the fluctuating component.

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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.

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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

Some Considerations concerning the Fluctuation of the Ratios of two Observables

We discuss several possible caveats which arise with the interpretation of measurements of fluctuations in heavy ion collisions. We especially focus on the ratios of particle yields, which has been advocated as a possible signature of a critical point in the QCD phase diagram. We conclude that current experimental observables are not well-defined and are without a proper quantitative meaning.

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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.

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arXiv2010

Elliptic flow fluctuations in heavy ion collisions at RHIC and the perfect fluid hypothesis

We analyse the recently measured $v_2$ fluctuation in the context of establishing the degree of fluidity of the matter produced in heavy ion collisions. We argue that flow observables within systems with a non-negligible mean free path should acquire a "dynamical" fluctuation, due to the random nature of each collision between the system's degrees of freedom. Because of this, $v_2$ fluctuations can be used to estimate the Knudsen number of the system produced at RHIC. To illustrate this quantitatively, we apply the UrQMD model, with scaled cross sections, to show that collisions at RHIC have a Knudsen number at least one order of magnitude above the expected value for an interacting hadron gas. Furthermore, we argue that the Knudsen number is also bound from above by the $v_2$ fluctuation data, because too large a Knudsen number would break the observed scaling of $v_2$ fluctuations due to the onset of turbulent flow. We propose, therefore that $v_2$ fluctuation measurements, together with an understanding of the turbulent regime for relativistic hydrodynamics, will provide an upper as well as a lower limit for the Knudsen number.

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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.

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arXiv2009

The use of Kolmogorov-Smirnov test in event-by-event analysis

We propose to use the Kolmogorov-Smirnov test to uncover non-statistical differences between events created in heavy ion collisions within the same centrality class. The advantage of the method over other approaches which are currently in use, is that it is sensitive to any difference between the events and is not restricted to simple moments of the distribution of hadrons. The particular application examined here is the identification of the fireball decay due to spinodal fragmentation and/or sudden rise of the bulk viscosity.

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arXiv2009

The Kolmogorov-Smirnov test and its use for the identification of fireball fragmentation

We propose an application of the Kolmogorov-Smirnov test for rapidity distributions of individual events in ultrarelativistic heavy ion collisions. The test is particularly suitable to recognise non-statistical differences between the events. Thus when applied to a narrow centrality class it could indicate differences between events which would not be expected if all events evolve according to the same scenario. In particular, as an example we assume here a possible fragmentation of the fireball into smaller pieces at the quark/hadron phase transition. Quantitative studies are performed with a Monte Carlo model capable of simulating such a distribution of hadrons. We conclude that the Kolmogorov-Smirnov test is a very powerful tool for the identification of the fragmentation process.

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arXiv2007

Why the $a_1$ meson might be a difficult messenger for the restoration of chiral symmetry

We perform a theoretical analysis of the $a_1$ resonance mass spectrum in ultra-relativistic heavy ion collisions within a hadron/string transport approach. Predictions for the $a_1$ yield and its mass distribution are given for the GSI-FAIR and the critRHIC energy regime. The potential of the $a_1$ meson as a signal for chiral symmetry restoration is explored. In view of the latest discussion, we investigate the decay channel $a_1 \to γπ$ in detail and find a strong bias towards low $a_1$ masses. This apparent mass shift of the $a_1$ if observed in the $γπ$ channel might render a possible mass shift due to chiral symmetry restoration very difficult to disentangle from the decay kinematics.

hep-ph↗

arXiv2006

Theoretical Analysis of Dilepton Spectra in Heavy Ion Collisions at GSI-FAIR Energies

This paper addresses the theoretical analysis of dilepton spectra in C+C collisions at GSI-SIS energies. Theoretical predictions for the recent data of the HADES collaboration at SIS-energies are made with the help of a hadron-string transport model, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. A mass shift of the $ρ$ meson due to kinematical effects is discussed.

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arXiv2005

Reconstructing $ρ^0$ and $ω$ mesons from non-leptonic decays in C+C at 2AGeV

We predict transverse and longitudinal momentum spectra and yields of $ρ^0$ and $ω$ mesons reconstructed from hadron correlations in C+C reactions at 2~AGeV. The rapidity and $p_T$ distributions for reconstructable $ρ^0$ mesons differs strongly from the primary distribution, while the $ω$'s distributions are only weakly modified. We discuss the temporal and spatial distributions of the particles emitted in the hadron channel. Finally, we report on the mass shift of the $ρ^0$ due to its coupling to the $N^*(1520)$, which is observable in both the di-lepton and $ππ$ channel. Our calculations can be tested with the Hades experiment at GSI, Darmstadt.

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arXiv2005

Resonance Absorption and Regeneration in Relativistic Heavy Ion Collisions

The regeneration of hadronic resonances is discussed for heavy ion collisions at SPS and SIS-300 energies. The time evolutions of Delta, rho and phi resonances are investigated. Special emphasize is put on resonance regeneration after chemical freeze-out. The emission time spectra of experimentally detectable resonances are explored.

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