Trajectum

Heavy ion collisions are an excellent laboratory to study properties of the quark-gluon plasma (QGP). Below is a theoretical prediction of the hydrodynamic expansion of the QGP produced in a central lead-lead collision at 5.02 TeV:

Code download

The above simulation was done using the Trajectum relativistic hydrodynamics code developed at Utrecht University, Massachusetts Institute of Technology and CERN. Trajectum is open source, the source code can be found here. For Ubuntu versions 20.04 or newer, there is also the option of installing a precompiled package with the following command:

sudo add-apt-repository ppa:g-h-nijs/trajectum && sudo apt update && sudo apt install trajectum

Installing in this way automatically resolves dependencies, and installs the required ones alongside Trajectum. However, since no CPU specific optimizations can be done, the resulting code will generally be faster when compiling from source. How much faster depends on the CPU, but on an 8th generation Intel i7, this difference is around 20%.

If you want to install just the dependencies required by Trajectum, but wish to compile Trajectum itself from source, you can install the libraries by replacing the apt install command above by the following:

sudo apt install liblhapdffortrajectum liblhapdffortrajectum-dev libfastjetfortrajectum libfastjetfortrajectum-dev libpythiafortrajectum libpythiafortrajectum-dev libgeminifortrajectum libgeminifortrajectum-dev smashfortrajectum

Note that whenever a paper mentions a specific version of Trajectum being used, this always refers to a minimally required version. Later versions of the code will also be able to reproduce the results.

Code usage

Before using the code, please read the readme.md file included in the source code (if you use the precompiled package this is installed at /usr/share/doc/trajectum/). It is in markdown format, which is human readable, but can be rendered in a browser with the appropriate browser extension, such as Markdown Viewer (chrome) for example (be sure to turn on file access so that it can render local files). The readme file contains not only compilation, but also usage instructions, so even if you installed Trajectum from the precompiled packages it is useful to read it.

The source code also includes example parameter files corresponding to 2010.15130, 2010.15134, 2110.13153, 2112.13771, 2203.13265, 2304.06191 , 2305.00015, 2307.11836, 2312.04623 and 2402.05995 so that one can reproduce the results with the exact same settings.

There is also an examples directory in the source code (installed at /usr/share/doc/trajectum/examples if using the precompiled package), which contains worked examples showing how to run the code along with mathematica notebooks which demonstrate some common observables, as well as instructions for how to compile Trajectum on a cluster such as lxplus.