arXiv subjects

H. Petersen

Publications and source records attributed to H. Petersen.

27 records · Page 2Linked to original sources

arXiv2010

Hydrodynamics with a chiral hadronic equation of state including quark degrees of freedom

We investigate the influence of a deconfinement phase transition on the dynamics of hot and dense nuclear matter. We apply a hybrid model where an intermediate hydrodynamics stage is employed for the the hot and dense stage of a system created in head-on collisions of Pb+Pb/Au+Au at beam energies from $2-160A $GeV. The initial and final interactions are performed by a microscopic transport approach (UrQMD). An equation of state that incorporates a critical end point (CEP) in line with lattice data is used. It follows from coupling the Polyakov loop (as an order parameter for deconfinement) to a chiral hadronic $SU(3)_f$ model. In this configuration the EoS describes chiral restoration as well as the deconfinemt phase transition. We compare the results obtained in this approach to results from a non interacting hadron resonance gas, focussing on observables deemed to be sensitive to the phase transition to the quark gluon plasma.

hep-ph↗

arXiv2009

Phi meson production in In-In collisions at $E_{\rm lab}$=158$A$ GeV: evidence for relics of a thermal phase

Yields and transverse mass distributions of the $ϕ$-mesons reconstructed in the $ϕ\toμ^+μ^-$ channel in In+In collisions at $E_{\rm lab}$=158$A$ GeV are calculated within an integrated Boltzmann+hydrodynamics hybrid approach based on the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model with an intermediate hydrodynamic stage. The analysis is performed for various centralities and a comparison with the corresponding NA60 data in the muon channel is presented. We find that the hybrid model, that embeds an intermediate locally equilibrated phase subsequently mapped into the transport dynamics according to thermal phase-space distributions, gives a good description of the experimental data, both in yield and slope. On the contrary, the pure transport model calculations tend to fail in catching the general properties of the $ϕ$ meson production: not only the yield, but also the slope of the $m_T$ spectra, very poorly compare with the experimental observations.

nucl-th↗

arXiv2009

A transport calculation with an embedded (3+1)d hydrodynamic evolution: Elliptic flow as a function of transverse momentum at SPS energies

The transverse momentum dependence of elliptic flow of pions calculated in a full (3+1)d Boltzmann approach with an intermediate hydrodynamic stage for heavy ion reactions for CERN-SPS energies is discussed in the context of the experimental data. At higher SPS energies, where the pure transport calculation cannot account for the high elliptic flow values, the smaller mean free path in the hydrodynamic evolution leads to larger elliptic flow. Due to the more realistic initial conditions and the incorporated hadronic rescattering the results are in line with the experimental data. Within this integrated dynamical approach different equations of state are applied without adjusting the initial state and the freeze-out conditions. We employ a hadron gas equation of state to investigate the differences in the dynamics and viscosity effects, a chiral equation of state with a moderate first order phase transition and a critical endpoint and a bag model equation of state with a large latent heat. The elliptic flow results are shown to be rather insensitive to changes in the equation of state.

nucl-th↗

arXiv2008

How Sensitive are Di-Leptons from Rho Mesons to the High Baryon Density Region?

We show that the measurement of di-leptons might provide only a restricted view into the most dense stages of heavy ion reactions. Thus, possible studies of meson and baryon properties at high baryon densities, as e.g. done at GSI-HADES and envisioned for FAIR-CBM, might observe weaker effects than currently expected in certain approaches. We argue that the strong absorption of resonances in the high baryon density region of the heavy ion collision masks information from the early hot and dense phase due to a strong increase of the total decay width because of collisional broadening. To obtain additional information, we also compare the currently used approaches to extract di-leptons from transport simulations - i.e. shining, only vector mesons from final baryon resonance decays and instant emission of di-leptons and find a strong sensitivity on the method employed in particular at FAIR and SPS energies. It is shown explicitly that a restriction to rho meson (and therefore di-lepton) production only in final state baryon resonance decays provide a strong bias towards rather low baryon densities. The results presented are obtained from UrQMD v2.3 calculations using the standard set-up.

hep-ph↗

arXiv2007

How can we explore the onset of deconfinement by experiment?

There is little doubt that Quantumchromodynamics (QCD) is the theory which describes strong interaction physics. Lattice gauge simulations of QCD predict that in the $μ,T$ plane there is a line where a transition from confined hadronic matter to deconfined quarks takes place. The transition is either a cross over (at low $μ$) or of first order (at high $μ$). It is the goal of the present and future heavy ion experiment at RHIC and FAIR to study this phase transition at different locations in the $μ,T$ plane and to explore the properties of the deconfined phase. It is the purpose of this contribution to discuss some of the observables which are considered as useful for this purpose.

nucl-th↗

arXiv2007

(3+1)-Dimensional Hydrodynamic Expansion with a Critical Point from Realistic Initial Conditions

We investigate a (3+1)-dimensional hydrodynamic expansion of the hot and dense system created in head-on collisions of Pb+Pb/Au+Au at beam energies from $5-200A$ GeV. An equation of state that incorporates a critical end point (CEP) in line with the lattice data is used. The necessary initial conditions for the hydrodynamic evolution are taken from a microscopic transport approach (UrQMD). We compare the properties of the initial state and the full hydrodynamical calculation with an isentropic expansion employing an initial state from a simple overlap model. We find that the specific entropy ($S/A$) from both initial conditions is very similar and only depends on the underlying equation of state. Using the chiral (hadronic) equation of state we investigate the expansion paths for both initial conditions. Defining a critical area around the critical point, we show at what beam energies one can expect to have a sizable fraction of the system close to the critical point. Finally, we emphasise the importance of the equation of state of strongly interacting matter, in the (experimental) search for the CEP.

nucl-th↗

arXiv2006

Longitudinal flow and onset of deconfinement

The effects of the onset of deconfinement on longitudinal and transverse flow are studied. First, we analyze longitudinal pion spectra from $E_{\rm lab}= 2A$ GeV to $\sqrt{s_{\rm NN}}=200$ GeV within Landau's hydrodynamical model and the UrQMD transport approach. From the measured data on the widths of the pion rapidity spectra, we extract the sound velocity $c_s^2$ in the early stage of the reactions. It is found that the sound velocity has a local minimum (indicating a softest point in the equation of state, EoS) at $E_{\rm beam}=30A$ GeV. This softening of the EoS is compatible with the assumption of the formation of a mixed phase at the onset of deconfinement. Furthermore, the energy excitation function of elliptic flow ($v_2$) from $E_{\rm beam}=90A$ MeV to $\sqrt{s_{\rm NN}}=200$ GeV is explored within the UrQMD framework and discussed in the context of the available data. The transverse flow should also be sensitive to changes in the equation of state. Therefore, the underestimation of elliptic flow by the UrQMD model calculation above $E_{\rm lab}= 30A$ GeV might also be explained by assuming a phase transition from a hadron gas to the quark gluon plasma around this energy. This would be consistent with the model calculations, indicating a transition from hadronic matter to ``string matter'' in this energy range.

nucl-th↗

arXiv2006

Anisotropic flow at RHIC: How unique is the number-of-constituent-quark scaling?

The transverse momentum dependence of the anisotropic flow $v_2$ for $π$, $K$, nucleon, $Λ$, $Ξ$ and $Ω$ is studied for Au+Au collisions at $\sqrt{s_{\rm NN}} = 200$ GeV within two independent string-hadron transport approaches (RQMD and UrQMD). Although both models reach only 60% of the absolute magnitude of the measured $v_2$, they both predict the particle type dependence of $v_2$, as observed by the RHIC experiments: $v_2$ exhibits a hadron-mass hierarchy (HMH) in the low $p_T$ region and a number-of-constituent-quark (NCQ) dependence in the intermediate $p_T$ region. The failure of the hadronic models to reproduce the absolute magnitude of the observed $v_2$ indicates that transport calculations of heavy ion collisions at RHIC must incorporate interactions among quarks and gluons in the early, hot and dense phase. The presence of an NCQ scaling in the string-hadron model results suggests that the particle-type dependencies observed in heavy-ion collisions at intermediate $p_T$ might be related to the hadronic cross sections in vacuum rather than to the hadronization process itself.

nucl-th↗

arXiv1994

Angular Dependent Soft X-ray Absorption Spectroscopy of V2O5 and V6O13

We have measured the V 2p3/2 and O 1s x-ray absorption spectra of single crystal V2O5 and V6O13 and compared to linear combinations of atomic orbitals (LCAO) density of states (DOS) calculations. The spectra change dramatically with incident angle. The use of polarized light and a single crystal limits the number of transitions possible, revealing spectral features that cannot be resolved on polycrystals (angle-integrated). The measured O 1s and V 2p3/2 spectra agree with the projected unoccupied O 2p and V 3d DOS respectively, indicating that atomic and solid state effects, including V-O hybridization, must be included to adequately describe the spectra.

cond-mat↗