Hijing

To use Hijing for simulation purposes, one must first run Hijing proper and generate event files, then feed these data to starsim to complete the GEANT part.

The Hijing event generator codes and makefile can be found in the STAR code repository at the following location:$STAR/pams/gen/hijing_382. Once built, the executable is named hijjet.x. The input file is called hijev.inp and should be modified as per user's needs. When the executable is run multiple times in same directory, a series of files will be produced with names like evgen.XXX.nt, where XXX is an integer. The format of the file is PAW Ntuple. The starsim application is equipped to read that format as explained below. If a large number of events are needed, a request should be made to the STAR simulation leader or any member of the S&C.

Listed below is the KUMAC macro that can be used to run your own GEANT simulation with pre-fabricated Hijing events . Unlike the Pythia simulation, events aren't generated on the fly but are read from an external file instead. Look at the comments embedded in the code. Additional notes:

  • don't forget to seed the random number generator if you'll be doing a series of runs
  • make sure you specify the correct geometry tag
  • specify a different output file for each run
  • the location of the input file (current directory) and the name (evgen.1.nt) are given as an example
  • you can browse the directory /star/simu/evgen to look at what input Hijing files are already available
  • the number of triggers on the bottom of the macro can be set to anything, just remember that the resulting files can be large and unwieldy if that number is too large. As a rule of thumb, we usually don't go over 500 events per file in production for min-bias AuAu, and 100 event for central gold 
gfile o my_hijing_file.fz
detp geom y2006
make geometry
gclose all
* define a beam with 100um transverse sigma and 60cm sigma in Z
vsig  0.01  60.0
* introduce a cut on eta to avoid having to handle massive showers caused by spectators
gkine -1 0 0 100 -6.3 6.3 0 6.3 -30.0 30.0
gexec  $STAR_LIB/gstar.so
us/inp hijing evgen.1.nt
* seed the random generator
rndm 13 17
* trigger - change to trigger the desired number of times
trig 10