History of Transport Model Code Comparisons
Transport models are indispensable to extract information about bulk properties of nuclear matter, including neutron-rich matter, from data obtained in heavy ion collisions. Due to many technical decisions that need to be made in implementing physical assumptions of the transport theory in simulation codes, a proliferation of codes has appeared in the last two decades, and divergent conclusions have sometimes been reached on the basis of the same data set. In an effort to narrow predictions and to quantify uncertainties in the results of transport simulations, the comparison of transport codes has been the topic of several workshops starting from the ECT* meetings in 2004, 2006 and 2009, the Transport2014 meeting in Shanghai and several shorter meetings after that.
We are now in the next phase of the comparison project which focuses on simulations of infinite nuclear matter, approximated by a box with periodic boundary conditions. We aim to disentangle different effects, like initialization, treatment of collision probabilities, Pauli blocking and mean field, all of which influence the results in a complicated way in heavy ion collision simulations. In box simulations it is easier to disentangle the different effects and to localize essential differences in the codes. Some preliminary results have been obtained, on comparing the effects of the collision term, the mean field propagation, and the role of fluctuations. We have also started box calculations to investigate the production mechanism of pions, which is an important probe to test the symmetry energy at high density. We will follow the successful strategy of the earlier Transport Workshops requesting that specified calculations be done by participants before the meeting.
The past transport meetings have a track record of publishing the code comparison results. "Transport Theories for Heavy Ion Collisions in the 1 AGeV Regime," J. Phys. G 31, S741 (2005) was published based on the results of the ECT* 2004 meeting. "Understanding transport simulations of heavy-ion collisions at 100A and 400A MeV: Comparison of heavy-ion transport codes under controlled conditions," Phys. Rev. C 93, 044609 (2016) was published after the Transport2014 meeting in Shanghai. We plan to work on publishing results from box simulations which will be discussed in Transport 2017 meeting.
Please contact the organizers if you are interested to participate in doing the homework associated with ICNT/Transport 2017 using your code.