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)
  • To get directly to the GSIM location an alias was set, so simply type

Running GSIM

Setting an Event Generator and create events file

  • The simple kinematic event generator we use at TAU is based on actual data:

e-e'p events in which 1 proton was detect serve as baseline to generation of a second proton, using the c.m. kinematics calculation

  • For jets/showers, PYTHIA and Lepto64 are used as the base-line event generator for GSIM
  • The existing EG is a ROOT macro located under $GSIM/EventGenerator/ directory.

Setting Event Generator

  • The EG should be modified for the specific solid target. An example for 12C can be found at

Generate the Events

  • To build the event generator use the build compilation command, e.g.
 root -l  eep_EG.C

(the result: an executable event generator e.g. lepto_exe/LeptoC.exe)

Look at the generated distributions

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

(the result: a different (just numbers) data file 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 C.txt) to the converter utility and convert it. e.g.
 ./txt2part -m -o12_100GeV.evt < 12_100GeV.txt 

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

Running generated events through a CLASS GEANT-3 simulation

running GSIM with the generated events

  • 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 with e.g. 12_100GeV.evt
 ./gsim_Batch.csh 12_100GeV
  • or simply use the run command
 RunGSIM 12_100GeV
  • gsim_*.bos contains the data 'collected' by CLASS (ADC/TDC)
  • gpp_*.bos incorporates preprocessing to add smearing of the data
  • outfile_* 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 gsim_*.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 gsim_*.bos
 ./bosdump gpp_*.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)

Writing the physical tree

  • The same way used to write the data file (utilizing write_tree.cxx) an executable is generated from write_simulation.cxx
  • write_simulation.cxx, apart from writing the EVNT bank data, also writes GSIM data
  • An example can be found at /u/home/cohen/Clas/WriteTreeEG2
  • A soft link is generated at /w/halla-scifs2/e07006/Erez/gsim/simulate/WriteTree so the only thing ones has to type is

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 following commands
 switch 1 2 
 dcut clas 2 0 10 10 0.015 0.015
 trig 1

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