A tool for converting the output of the neut simple generator (neutroot2) to a RooTracker-like format.

NEUT is a neutrino event generator. It is not currently open source, but is in use by a number of collaborations in the neutrino physics community. It is often useful to compare the predictions of multiple generators to each other, to facilitate this it is useful to have a common format. The other two major, modern neutrino event generators GENIE (https://github.com/GENIEMC) and NuWro (https://github.com/cjusz/nuwro) are both able to have their outputs converter to a 'rooTracker'-like output with bundled executables. NEUT is able to produce an output in this format, but only when running in full detector geometry simulation mode. This program aims to allow the output of the simple neutrino event generator module of NEUT to be simply converted to a compatible format for a unified analysis.

• ROOT: https://github.com/root-mirror/root
• NEUT: Not freely available. Sorry.

$ git clone https://github.com/luketpickering/NeutToRooTracker.git

$ git submodule init; git submodule update

Depending on how your NEUT install is built export an environment variable to point to the source or binary install tree.

1. Using default NEUT build scripts:

   $ export NEUT_ROOT=</path/to/neut>

2. Using cmake built NEUT:

   $ export NEUT_INSTALL_ROOT=</path/to/neut/install>

Your NEUT install must be successfully built, and this environment variable set before attempting to build NeutToRooTracker.exe

$ source /<path/to/root>/bin/thisroot.sh
$ source setup.sh

This will add the bin directory to your $PATH variable if it isn't already included.

$ cd neut2rootracker; make

$ cd neut2rootracker; make [docs|latex_docs]

Command line options all have a short form and a long form and either take 1 or 0 arguments.

• -i|--input-file <TChain::Add descriptor> [required]:

  Input file descriptor. Input files are NEUT vector format files, as produced by the neutroot2 executable. This string is passed to TChain::Add so may contain wildcards to read multiple input files. N.B. if wildcards are used the argument should be wrapped in double quotes to stop the calling shell expanding the wildcard.

• -o|--output-file <output_file.root>:

  The name of the output rootracker file. Defaults to vector.ntrac.root.

• -n|--nentries <integer>:

  Maximum number of input file entries to process. Defaults to -1 which specifies that all input entries should be processed.

• -v|--verbosity:

• -G|--GeV-mode:

  Assumes all input units are MeV and scales all energy and momentum values by 1.0/1000.0.

• -O|--objectify-output:

  If enabled, the output tree will contain a single branch of NRooTrackerVtx (or NRooTrackerVtxB in the case of Lite output mode) instances with data members exposing the RooTracker information.

• -b|--save-isbound:

  For a target with extra free protons, such as CH, NEUT will not specify a different target PDG code if the event happened on a free proton. This option adds an extra branch to the output tree which specifies whether the interaction occured off of a bound nucleon.

• -L|--Lite-Mode:

  Output a significantly reduced data set for smaller output files. This will not output any of the NEUT-specific interaction information or FSI history.

• -E|--Emulate-NuWro:

  Outputs a slightly modified StdHep flavor which more closesly mimics the NuWro RooTracker output. The target nucleon and target nucleus are condensed into a single StdHep entry with the PDG specifying the target nucleus and the StdHepP4 being that of the target nucleon.

• -S|--Skip-non-FS:

  If enabled, the output StdHep tree will contain no final state particles that did not make it out of the nucleus (NEUT fStatus!=[0,2], fIsAlive!=1). N.B. If not using Lite mode then all final state information will be available in the NEUT NE and NF common block output.

• -I|--Ignore-NEUT-Modes <integer,integer,integer,...>:

  Accepts a comma separated list of NEUT interaction mode specifiers to ignore. Input entries with one of the ingored modes are not processed and not saved to the output file. A digest of ignored entries is written to stdout at the end of processing.

The basic StdHep portion of the NEUT flavor RooTracker format is described here:

• Int_t EvtCode //Interaction Mode --- CCQE == 1
• Int_t StdHepN //Number of particles stored in other StdHep Arrays
• Int_t StdHepStatus[$i<$StdHepN] //Status code of particle i --- 0 == incoming, 11 == incoming nucleus (if not using -E), 1 == good final state, anything else == intermediate or unseeable particle.
• Int_t StdHepPDG[i<StdHepN] //PDG code of particle i --- 14 == nu_mu, 13 == mu, 2212 == p, 2112 == n
• Int_t StdHepP4[i<StdHepN][4] //Four momentum of particle i --- StdHepP4[i][3] == E_i.

For other branches that are included when not running with -L see the member documentation of NRooTrackerVtx.

• Output by default is in units of MeV: To output in GeV pass -G CLI option.

• If the StdHepStatus != 1 then you didn't see that particle. Always check the StdHepStatus.

• For input files which contain NEUT flux and event rate histograms the EvtWght and NEntriesInFile branches of non-Lite mode are filled. EvtWght = event_rate->Integral()/flux->Integral(). To correctly normalise a flux averaged final state property histogram each entry should be weighted by EvtWght*1E-38/NEntriesInFile, this will put the y axis in units of cm^2 nucleon^-1. N.B. it is a good idea to also scale by bin width^-1.

• NEUT will output Pauli blocked events, these will make it through to the final output and will be events with no StdHepStatus[i]==1 final state particles.

• If not emulating NuWro the struck nucleon entry will have StdHepStatus==11 similar to GENIE.