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Die theoretische Physikerin Hannah Elfner erhält für ihre Forschung zu Ereignissen kurz nach dem Urknall den Preis »Scientist of the Year« 2021. Ein Gespräch über das Warten auf Daten, über die Rolle von Visualisierungen vom »Little Bang« und die Betreuung von Studierenden.

In this work, the qualitative impact of the net baryochemical potential dependence of the shear viscosity to entropy density ratio $η/s$ in hydrodynamical simulations is studied. The effect of a predicted non-constant $η/s$($μ_B$) is largely unexplored in hydrodynamic simulations. Previous studies focus only on a temperature dependence or even only a constant effective shear viscosity. This work addresses this issue by studying qualitatively the effect of a generalized $η/s$($T,μ_B$) in the hybrid approach SMASH-vHLLE, composed of the hadronic transport approach SMASH and the (3+1)d viscous hydrodynamic code vHLLE. In order to reduce the bias of the result on the equation of state used in the hydrodynamic part of the model, $η/s$ is parameterized directly in the energy density and net baryon number density. The parameterization takes into account the constraints of matching to the transport coefficients in the hadronic phase, as well as pQCD results. This work compares the impact of the density dependence for different system sizes and energies and compares the observables with experimental results in the RHIC - BES region $\sqrt{s_{NN}}$ =7.7 - 39.0 GeV, as the effect of this generalization is especially relevant for intermediate collision energies, for which the system is in equilibrium for a relevant amount of time, but the net baryochemical potential does not vanish. It is shown that the effect of an explicit net baryon number dependence on the elliptic flow is negligible and only relevant in the early stages of the collision. Additionally, we find that the proposed parameterization could be a good proxy for the shear viscosity in the non-equilibrium hadronic transport stage., 11 pages, 12 figures

Optical photons, created from fluorescence or Cherenkov emission in atmospheric cascades induced through high energetic cosmic rays are of major interest for several experiments. Experiments like CTA require a significant amount of computing time and funds for the simulation with CORSIKA 7. Since individual photons don’t interact they can be simulated without any order. The traditional sequential approach is simple but leads to reduced utilization of modern hardware infrastructure. The calculations done on each photon have low complexity, compared to the other aspects of the simulation. This, as well as the fact that, besides information about the photon itself, nearly no additional data is needed, favors a data-parallel approach in which several photons are propagated concurrently. The new CORSIKA 8 framework enables the implementation and verification of these methods. With the use of dedicated high parallel acceleration hardware like GPUs the possible benefits with this data-parallel approach are even higher.

Physical review / C 103(4), 044904 (2021). doi:10.1103/PhysRevC.103.044904, Heavy-ion collisions at low beam energies explore the high density regime of strongly interacting matter. The dynamical evolution of these collisions can be successfully described by hadronic transport approaches. In March 2019, the HADES Collaboration took data for AgAg collisions at EKin=1.58AGeV, and in this work we provide predictions for particle production and spectra within the Simulating Many Accelerated Strongly interacting Hadrons (smash) approach. The multiplicities and spectra of strange and nonstrange particles follow the expected trends as a function of system size. In particular, in ArKCl (and pNb) collisions, much higher yields of double-strange baryons were observed experimentally than expected from a thermal model. Therefore, we incorporate a previously suggested mechanism to produce Ξ baryons via rare decays of high mass N* resonances and predict the multiplicities. In addition, we predict the invariant mass spectrum for dilepton emission and explore the most important sources of dileptons above 1 GeV, that are expected to indicate the temperature of the medium. Interestingly, the overall dilepton emission is very similar to the one in AuAu collisions at 1.23AGeV, a hint that the smaller system at a higher energy behaves very similarly to the larger system at lower beam energy., Published by Inst., Woodbury, NY

Physical review / C covering nuclear physics 99(4), 044907 (2019). doi:10.1103/PhysRevC.99.044907, Published by APS, Woodbury, NY

The 27th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions, Quark Matter 2018, Venice, Italy, 13 May 2018 - 19 May 2018; Nuclear physics / A 982, 807 - 810 (2019). doi:10.1016/j.nuclphysa.2018.09.008, Published by North-Holland Publ. Co., Amsterdam