Vector Meson Spectral Functions in a Coarse-Graining Approach

Dilepton production in heavy-ion collisions at top SPS energy is investigated within a coarse-graining approach that combines an underlying microscopic evolution of the nuclear reaction with the application of medium-modified spectral functions. Extracting local energy and baryon density for a grid of small space-time cells and going to each cell's rest frame enables to determine local temperature and chemical potential by application of an equation of state. This allows for the calculation of thermal dilepton emission. We apply and compare two different spectral functions for the $\rho$: A hadronic many-body calculation and an approach that uses empirical scattering amplitudes. Quantitatively good agreement of the model calculations with the data from the NA60 collaboration is achieved for both spectral functions, but in detail the hadronic many-body approach leads to a better description, especially of the broadening around the pole mass of the $\rho$ and for the low-mass excess. We further show that the presence of a pion chemical potential significantly influences the dilepton yield.Comment: 9 pages, 2 figures; Contribution for proceedings of the Resonance Workshop in Catania 201

Dilepton Production in Transport-based Approaches

We investigate dilepton production in transport-based approaches and show that the baryon couplings of the $\rho$ meson represent the most important ingredient for understanding the measured dilepton spectra. At low energies (of a few GeV), the baryon resonances naturally play a larger role and affect already the vacuum spectra via Dalitz-like contributions, which can be captured well in an on-shell-transport scheme. At higher energies, the baryons mostly affect the in-medium self energy of the $\rho$, which is harder to tackle in transport models and requires advanced techniques.Comment: 4 pages, 3 figures, PANIC 2014 proceeding

Dimethyl ether in its ground state, v=0, and lowest two torsionally excited states, v11=1 and v15=1, in the high-mass star-forming region G327.3-0.6

The goal of this paper is to determine the respective importance of solid state vs. gas phase reactions for the formation of dimethyl ether. This is done by a detailed analysis of the excitation properties of the ground state and the torsionally excited states, v11=1 and v15=1, toward the high-mass star-forming region G327.3-0.6. With the Atacama Pathfinder EXperiment 12 m submillimeter telescope, we performed a spectral line survey. The observed spectrum is modeled assuming local thermal equilibrium. CH3OCH3 has been detected in the ground state, and in the torsionally excited states v11=1 and v15=1, for which lines have been detected here for the first time. The emission is modeled with an isothermal source structure as well as with a non-uniform spherical structure. For non-uniform source models one abundance jump for dimethyl ether is sufficient to fit the emission, but two components are needed for the isothermal models. This suggests that dimethyl ether is present in an extended region of the envelope and traces a non-uniform density and temperature structure. Both types of models furthermore suggest that most dimethyl ether is present in gas that is warmer than 100 K, but a smaller fraction of 5%-28% is present at temperatures between 70 and 100 K. The dimethyl ether present in this cooler gas is likely formed in the solid state, while gas phase formation probably is dominant above 100 K. Finally, the v11=1 and v15=1 torsionally excited states are easily excited under the density and temperature conditions in G327.3-0.6 and will thus very likely be detectable in other hot cores as well.Comment: 12 pages (excluding appendices), 8 figures, A&A in pres

Distinct cell shapes determine accurate chemotaxis

Biological and Soft Matter Physic