FIST sampler

Description

FIST sampler is an implementation of the Cooper-Frye particlization sampling procedure for heavy-ion collisions based on a thermal-statistical package Thermal-FIST

The sampler uses a particlization hypersurface produced in hydro simulations (such as using MUSIC) and samples hadrons and resonances from it. Optionally, the chain of decays can then be performed.

A distinctive feature of the sampler is the ability to selectively incorporate the exact (the canonical ensemble) global conservation of conserved charges, such as baryon number, electric charge, strangeness, and charm. It also incorporates the effect of baryon repulsive core (excluded volume), in accordance with the EV-HRG model formulated in https://arxiv.org/abs/1708.02852

The sampling procedure first determines the numbers of each hadrons species to be sampled in a given event, and then the momentum of each hadrons is sampled independently from other hadrons. This is different from the more conventional Cooper-Frye sampling and allows one to sample the events with the canonical treatment of conserved charges considerably faster. The downside is that the routine requires a considerable amount of memory, in practice about ~5-15 GB for central Au-Au collisions.

The description of the sampling procedure can be found in Appendix B of the paper https://arxiv.org/abs/2107.00163

Currently the sampling does not incorporate viscous corrections.

Prerequisites

A compiler with C++11 support.
CMake v3.1+.

Building

For a Linux system:

# Clone the repository fetching the submodule(s)
git clone --recurse-submodules https://github.com/vlvovch/fist-sampler.git

# Create the build directory and build the project
cd fist-sampler
mkdir build
cd build
cmake ../
make FISTSampler

Usage

./FISTSampler <input-file>

Here input-file contains the parameters for the sampling.

Examples

See input/input.AuAu.7.7.C0-5 for a sample input corresponding to 0-5% central Au-Au collisions at 7.7 GeV, which includes the description of all the relevant parameters. See also input/input.AuAu.7.7.C0-5.EVHRG for a sample input which includes the excluded volume effect for (anti)baryons.

The sampler requires an input file with the particlization hypersurface. One of the supported formats is the binary output from MUSIC. Such hypersurfaces are available here, based on a paper https://arxiv.org/abs/2003.05852. To download the MUSIC hypersurfaces corresponding to 0-5% Au-Au collisions at various RHIC-BES energies run e.g.

bash ../input/get_MUSIC_input_RHICBES.sh

from the build directory. This will take ~1.5GB of space, this space can be reduced by omitting collision energies that are not needed. Note that the script requires the gdown package to be installed. If this does not work, just download the files from Google Drive manually.

Then, to sample Au-Au collisions at 7.7 GeV run

./FISTSampler ../input/input.AuAu.7.7.C0-5

This should generate 1000 collisions with the canonical treatment of baryon number in ascii output file AuAu.7.7.C0-5.events.dat

The input folder contains also other systems. For instance, input/input.HADES.AuAu.2.4.C0-5 and input/input.HADES.AuAu.2.4.C0-5.EVHRG correspond to Siemens-Rasmussen-Hubble model based event generator of 0-5% central 2.4 GeV Au-Au collisions corresponding to the HADES experiment, with and without the excluded volume effect, respectively. On other hand, input/input.ALICE.PbPb.2760.C0-5 and input/input.ALICE.PbPb.2760.C0-5.EVHRG correspond to blast-wave model based event generator of 0-5% 2.76 TeV Pb-Pb collisions.

Attribution

Publications using this sampler should include a reference to the Thermal-FIST package

V. Vovchenko, H. Stoecker, Thermal-FIST: A package for heavy-ion collisions and hadronic equation of state, Comput. Phys. Commun. 244, 295 (2019) [arXiv:1901.05249 [nucl-th]]

as well as the paper

V. Vovchenko, V. Koch, C. Shen, Proton number cumulants and correlation functions in Au-Au collisions at 7.7−200 GeV from hydrodynamics, Phys. Rev. C 105, 014904 (2022) [arXiv:2107.00163 [nucl-th]]

describing the sampling procedure.

In addition, if third-party input is used (such as the particle list or hypersurface of particlization), please cite the relevant literature.