Interfacing jet quenching and hydrodynamic evolution

Interfacing jet quenching and hydrodynamic evolution

One of the tasks agreed upon by the Hard Probes session at the TECHQM I workshop was to develop a documented output file standard for the time-evolution of hydrodynamic models and also a format for the freeze-out hypersurface of a hydro calculation.

Such standardized output formats would greatly facilitate the collaboration of different groups doing jet-quenching, lepton/photon and heavy-quark diffusion calculations with the different hydro groups. It follows in the spirit of the OSCAR initiative [1], whose biggest and enduring success was the creation of a standardized output format for particle-based transport models.

Please note that the support of a standardized hydro output format does not say anything about how the hydro practitioners individually choose to collaborate and disseminate the results of their calculations.

As a result of a first solicitation email for suggestions to the new standard format, as well as a discussion at the June 2008 TECHQM phone conference, the following consensus has been reached on how to proceed:

1. a standardized output file format will be created
2. subsequently, also a set of standard routines which serve as interface between (either the proprietary or standardized) output by the different hydro groups and which deliver the relevant information (e.g. temperature, mu_B as a function of tau and location) for the respective hydro model will be developed and provided

Both the file format as well as the interface routines can be considered milestones which should be addressed and worked out over the 2nd half of 2008. In the following, considerations for both approaches are outlined - these will morph into a to-do list for the completion of the two milestones.

Considerations / specifications for a standardized output format

The requirement is an output format which is of flexible enough structure that it can accommodate:

• 2+1 as well as 3+1 dimensional calculations
• Eulerian and Lagrangian grids
• eta-tau as well as cartesian coordinates
• ideal and viscous hydro calculations
• do so without wasting file space, i.e. writing out only the real information present, dependent on the dimensionality and nature of the code (2D vs. 3D and ideal vs. viscous)

A starting point for a more detailed discussion can be found in the form of the OSCAR2000H draft for a standard hydro output format [2], which however needs to be amended to make provisions for viscous hydro codes and Lagrangian grids. It is planned to circulate a first draft for a standard output format among the practitioners before the August TECHQM phone conference.

Considerations / specifications for a set of standardized interface routines

The biggest advantage of standardized interface routines is the ability to interpolate between the hydro cells and provide thermodynamic quantities as a smooth function of of position, no matter the structure of the underlying grid. Tetsufumi Hirano has posted the time evolution for his 3D hydro along with a set of routines to read them in at [3] - these routines may serve as a basis for the forthcoming discussion.

Additional points to be discussed in the context of defining these routines are:

• what information should be accessible via these routines?
• should the interpolation between the cells be conducted in a specific manner or is this free for the developer of the respective hydro to decide?
• are the routines to be supplied in FORTRAN or C or both?
• Naming convention of the routines to distinguish different hydro models from each other (this of course would be a mote point if we agree to have one standard output format and one standard set of interface routines)

OSCAR Standard Output Format for Hydro Codes

(created by Steffen A. Bass, June 2008, last edit by Bass 27 July 2009 (EDT)

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