Simulations Working Group (SIMS-WG)


SIMS-WG assists in writing, maintaining and running physics and statistical software for modeling heavy ion collisions, as well as performing state-of-the-art model-to-data comparisons. 

In arXiv:2010.03928 and arXiv:2011.01430, we presented a Bayesian inference on measurements from the RHIC and the LHC. We obtained state-of-the-art constraints on the shear and bulk viscosities of QCD, and applied for the first time in heavy ion studies multiple new concepts of Bayesian inference, including:

  • Closure tests
  • Critical examination of priors
  • Bayesian model selection
  • Bayesian model averaging
Click on the image to access a widget that shows how each model parameters affect hadronic observables.

See below for description of the components used for modeling the soft sector of heavy ion collisions.

The first stage of the model gives the initial conditions. TRENTo is a model which parameterizes the initial energy deposition immediately following a heavy ion collision. 

The first dynamical stage of the collision is treated with a free-streaming approximation. The system expands and cools, before we match the full energy-momentum tensor to viscous hydrodynamics. 

The second dynamical stage is relativistic viscous hydrodynamics, solved by MUSIC. The system continues to expand and cool according to parameterized transport coefficients and a fixed equation of state. 

At a switching temperature, the energy-momentum tensor of hydrodynamic is converted into distributions of hadrons. The model of “particlization” used are those included in the iS3D sampler. 

SMASH is a model for evolving a system of hadrons according to a coupled Boltzmann equation. Hadrons can scatter, form resonances and decay until they finally become completely decoupled. 


PhD Students


External Members

Jean-François Paquet

(Duke University)

Gojko Vujanovic

(Wayne State University)


Lipei Du

(Ohio State University)

Derek Everett

(Ohio State University)

Matthew Heffernan

(McGill University)
Dan Liyanage
(Ohio State University) 

Weiyao Ke

(UC Berkeley and LBNL)

Steffen Bass

(Duke University)

Charles Gale

(McGill University)

Abhijit Majumder

(Wayne State University)

Chun Shen

(Wayne State University)

Ulrich Heinz

(Ohio State University)

Matthew Luzum

(University of São Paulo)