Running GSIM CLAS simulation

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GSIM Inventory

  • GSIM directory is to be located on the farm, at a large enough work disk. An example of the simulation inventory can be found at
 /work/halla/e07006/disk1/Erez/GSIM  (will be used for the remainder of the documentation as $GSIM)

Running GSIM

Setting an Event Generator and create events file

  • PYTHIA is used as the base-line event generator (EG) for GSIM
  • The existing EG is a fortran script located under $GSIM/Documents/ directory.

Setting Event Generator

  • The EG should be modified for the specific solid target. An example for 12C can be found at
  • To build the event generator use the build compilation command, e.g.
 cd  $GSIM/Documents/

(the result: an executable event generator e.g. EventGenerator_exe/EG_C.exe)

Generate the Events

  • Generate the events by executing the EG, e.g.
 ./EG_C.exe > test.dat

(the result: a data file EventGenerator_exe/test.dat)

Look at the generated distributions

  • A utility for observing the generated data exist in the main EG directory $GSIM/Documents/EventGenerator/LeptoRoot
  • Port the data file into the utility directory
 cp $GSIM/Documents/EventGenerator_exe/test.dat $GSIM/Documents/LeptoRoot/
  • A perl script is used to write it in the right format
 ./ < test.dat > data.dat 

(the result: a different (just numbers) data file LeptoRoot/data.dat)

  • An executable is then used to write the data into a ROOT TTree

(the result: a ROOT file LeptoRoot/data.root that will enable you to observe the generated distributions)

Converting generated data files to GEANT-3 format input

  • port the generated-events data file (in this example test.dat) to the converters utility and convert it to txt format.

For example, a file from the 2H target would be converted by

 cp $GSIM/Documents/EventGenerator_exe/test.dat $GSIM/converters
 ./convert_deut < test.dat > convert_output.dat

(the result: a txt file /converters/convert_output.dat )

  • port and convert the txt file to a G3 part format corresponding to the MCTK bank (works better than particle bank in G3)
 mv convert_output.dat  ../Lepto64
 cd ../Lepto64
 ./txt2part -m -omctk.evt < convert_output.dat 

(the result: a part file /Lepto64/mctk.evt suitable for GSIM)

Running generated events through a CLASS GEANT-3 simulation

running GSIM with the generated events

  • port the events file to the shared directory
 mv mctk.evt share
 cd share
  • to run the first XXXX events through the simulation, modify the file so that it triggers XXXX events
  • then execute the shell script that runs GSIM

(the result: 2 bos + 1 txt files , gsimtest.txt, gsimtest.bos, gpp_test.bos and the output file outfile1 )

  • gsimtest.bos contains the data 'collected' by CLASS (ADC/TDC)
  • gpp_test.bos incorporates preprocessing to add smearing of the data
  • outfile1 is the physical data after REConstruction SYStem analyzed it

Look at the output files

  • using COUNTBS one could count the number of events, e.g.
 ./countbs gsimtest.bos

(Note the first additional two events are header and are not to be accounted)

  • using BOSDUMP code, one can look at the data from the terminal, e.g.
 ./bosdump gsimtest.bos
 ./bosdump gpp_test.bos

Converting the GSIM output file to ROOT

  • this is the easy part now. For an output file named outfile1 e.g., use
 ./WriteRootDst -o output.root -GSIM outfile1

(the result: a root file /output.root)

Observing the output ROOT TTree

  • The ROOT TTree is called
  • To look at the data use e.g.
 CLASEVENT -> StartViewer()
  • The 'collected data' is stored in EVNT.XXXX variables, while the generated data is stored in GSIM.XXXX variables.

Running GSIM in interactive mode

  • follow the steps up to ./gsim_test.csh (without executing the shell script!)
  • source the necessary environmental set-ups
 source /group/clas/builds/environment.csh
  • run GSIM
 gsim_int -ffread -mcin XXXX.evt

(where XXXX.evt is the event file, e.g. mctk.evt)

  • inside GSIM you will be prompted to answer a question. disregard it (type \return)
  • execute the folloeing commands
 switch 1 2 
 dcut clas 2 0 10 10 0.015 0.015
 trig 1

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