# Au+Au200 (OSCAR2008H)

Essential profiles for jet quenching in viscous hydro (OSCAR2008H format)

Note: The output files described on this page contain similar, but not exactly the same hydrodynamic output as described on the previously posted page (2+1)-dimensional viscous fluid dynamics (VISH2+1 with EOSL-PCE, Shen, Huovinen et al.). Here a slightly different soft/hard mix (70% wounded nucleon + 30% binary collision weighting in the entropy density) was used in the Glauber model initialization, in order to better reproduce the measured centrality dependence of dN_ch/dy once the different rates of viscous entropy production in central and peripheral collisions is taken into account. Also, the hydrodynamic evolution was started at \tau_0=0.6 fm/c (instead of 0.4 fm/c) because earlier starting times require using smaller time steps initially for accuracy but larger time steps later to keep the file dimensions manageable, and this would have complicated reading the files posted here.

The output files can be downloaded from OSCAR_Au+Au. To unzip the tarballs type "tar -jxvf filename.tar.bz2". These results were computed with VISH2+1 (arXiv:0709.0742, arXiv:0712.3715, and arXiv:0805.1756), a viscous hydro code in (2+1) dimensions assuming longitudinal boost invariance, for Au+Au collisions at sqrt(s_NN) = 200 GeV.

File names: The files are named by model and impact parameter. For example, the file Glbb0887.tar.bz2 has the output for Au+Au collisions at impact parameter b=8.87fm ('b0887') for a Glauber model ('Glb') initial entropy density profile; the file CGCb1110.tar.bz2 contains output for collisions at b=11.10fm with an fKLN ('CGC') initial entropy density profile.

EOS: The simulations use the equation of state s95p-PCE developed by Pasi Huovinen and Peter Petreczky that matches lattice QCD data at high temperatures to a chemically frozen-out hadron resonance gas at low temperatures. A detailed description of EOS s95p-PCE is given in arXiv:1010.1856.

Contents: Each file contains the complete hydrodynamic output (ideal and viscous terms) at the full numerical resolution of the hydrodynamic simulation (i.e. at every available space-time grid point). The files are correspondingly large (between 500 MB at the largest and 900 MB at the smallest impact parameters whose fireballs live the longest). Please consult the description of the OSCAR2008H format to understand the organization of the output in these files. To facilitate reading the files we have also posted a short piece of FORTRAN code that reads the header lines and hydro output for the first time step: readOSCAR.for.

Initial conditions for the hydro evolution are adjusted to roughly reproduce experimental pion and proton spectra from the 5% most central 200 A GeV Au+Au collisions, using EOS s95p-PCE:

s_0 = 109 fm^-3 [peak entropy density in the Glauber model at \tau_0 for b = 0 (central collisions)]

\tau_0 = 0.6 fm/c

T_dec = 130 MeV

\eta/s = 0.20

We use the optical Glauber and CGC models to compute the shape of the initial entropy density profile and convert it to an initial energy density profile using EOS s95p-PCE. For the Glauber model entropy density we use a 70%/30% wounded nucleon/binary collision mix. The initial entropy density profiles for the CGC model were computed with the optical model version of the fKLN code. The CGC initial conditions were normalized to the same total initial entropy dS/dy as for the Glauber model at b=7.5fm. This gives almost identical final charged hadron multiplicities dN_ch/dy for the models at b=7.5fm (within 0.2%). With this normalization, both models give a good description of the centrality dependence of dN_ch/dy over the entire impact parameter range; the final multiplicities agree exactly at b=7.5fm and approximately at other impact parameters.

Important note: These parameters do not provide a "best fit" to experimental data (in particular, the measured differential elliptic flow v2(pT) of charged particles is underpredicted, especially so for Glauber initial conditions). The above files should only be used for qualitative studies that do not require precise reproductions of the soft hadron spectra and elliptic flow, but for which a semi-realistic model of the evolution of the fireball medium is sufficient. A comparison of the spectra and elliptic flow from the attached calculations with experimental data is shown in arXiv:1010.1635.

NB: The relatively "large" eta/s used here (about 2.5 times the KSS bound) leads to significant viscous entropy production (about 50%). The same final multiplicity thus requires a smaller initial entropy density than in ideal fluid dynamics. On the other hand, the larger binary collision weight (30%) in the Glauber model, compared to earlier calculations, leads to a more strongly peaked initial entropy density profile; the same initial entropy thus corresponds to a larger peak value s_0 in the fireball center. This is why s_0=109fm^(-3) is close to values used earlier, in spite of viscous entropy generation.

Collision centralities: We have posted results for the following impact parameters and corresponding centrality ranges:

b = 3.16fm (0-10%), 5.78fm (10-20%), 7.49fm (20-30%), 8.87fm (30-40%), 10.1fm (40-50%), and 11.1fm (50-60%).

We use the same T_dec, \tau_0, and \eta/s as above for all b.

All users of these output files must give proper credit to Chun Shen who performed the calculations, to Pasi Huovinen who provided the EOS, and to Huichao Song and U. Heinz who developed VISH2+1. Please refer to the following two papers:

C. Shen, U. Heinz, P. Huovinen and H. Song, Systematic parameter study of hadron spectra and elliptic flow from viscous hydrodynamic simulations of Au+Au collisions at sqrt(s_NN) = 200 GeV (arXiv:1010.1856)

T. Renk, H. Holopainen, U. Heinz and C. Shen, A systematic comparison of jet quenching in different fluid-dynamical models (arXiv:1010.1635) (this paper uses the attached profiles for jet quenching studies).

Posted by U. Heinz on 17 Nov. 2010, 7:00pm; updated by UH on Nov. 18, 2010, 11:59am