SMASH ROOT output has the same functionality as OSCAR output, but ROOT files are faster to read and write and they need less disk space for the same amount of information. This is achieved due to an optimized internal structure of ROOT files (and compression). ROOT files are not human-readable, but they can be viewed using ROOT's TBrowser. One can also access them using ROOT functions. The full memory structure of the ROOT files can be found here: http://root.cern.ch/root/html/TFile.html. We only desribe the logical structure of the SMASH ROOT output. Knowing the logical structure is enough to read and write ROOT files and understand their view in TBrowser.

Producing ROOT output requires ROOT installed (see http://root.cern.ch).

SMASH produces one ROOT file per run: smash_run.root. This file contains a TTree called particles and a TTree called collisions, depending on the required content (see Output). The particles tree contains the same information as OSCAR particles output and the collisions tree contains the same information as OSCAR collision output.

In case that the ROOT format is used for dilepton output (see Dileptons), the file is called Dileptons.root and only contains a collisions tree with all the dilepton decays.

Every physical quantity is in a separate TBranch. One entry in the particles TTree is:

ev tcounter npart impact_b pdgcode[npart] t[npart] x[npart] y[npart]

z[npart] p0[npart] px[npart] py[npart] pz[npart]

One tree entry is analogous to an OSCAR output block, but the maximal number of particles in one entry is limited to 10000. This is done to limit the buffer size needed for ROOT output. If the number of particles in one block exceeds 10000, then they are written in separate blocks with the same tcounter and ev. The fields have the following meaning:

ev is event number
tcounter is number of output block in a given event in terms of OSCAR
npart is number of particles in the block
impact_b is the impact parameter of the event
pdgcode is PDG id array
t, x, y, z are position arrays
p0, px, py, pz are 4-momenta arrays

The entries in the collisions tree are organized in the same way, but a few additional fields are present:

nin and nout are added to characterize number of incoming and outgoing particles in the reaction, with nin + nout = npart.
weight is an action weight, whose meaning depends on the type of action: For collisions it is the total cross section, for decays it is the total decay width and for dilepton decays it is the shining weight.

Currently writing initial and final configuration to collisions tree is not supported.