STAR  Computing  Simulation  
Hijing in STAR
  Maintained by Maxim Potekhin

What is Hijing and how do I run it?


The HIJING code in STAR

We in STAR use a wrapper for the core HIJING functions, which allows us to produce the output in the Ntuple file format, which is an internal STAR standard. This makes it possible to interface multiple event generators in a consistent manner. Also, as a bonus, we propagate such event specific information as the number of binary collisions etc, to the GEANT stage of the simulation and further to reconstruction, aiding the physics analysis.

The code resides in CVS and typical users would probably not need to compile it themselves. For reference, the location is $STAR/pams/gen/hijing_382, and the makefile is supplied there as well.

Running HIJING in standalone mode

You need the executable hijjet.x and the input file hijev.inp to run Hijing. The executable (currently compiled on Red Hat 8.0 with gcc compiler version 3.2) is located in the $STAF/.rh80_gcc32/bin/ and you should verify the path by using which hijjet.x.

The file hijev.inp can be based on the following template:

'  ====================================================== '   
'  =====         Hijing Control file                ===== '   
'  ====================================================== ' 
' Events                          '  100
' Frame/Energy                    '  'CMS'  200.              
' Projectile  type/A/Z            '  'A'  197 79              
' Target      type/Z/Z            '  'A'  197 79         
' Impact parameter min/max (fm)   '  0.   20.                  
' Jet quenching (1=yes/0=no)      '  0                        
' Hard scattering/pt jet          '  0   2.0                   
' Max # jets per nucleon (D=10)   '  10                        
' Set ihpr2(11) and ihpr2(12)     '  1   1
' Set ihpr2(21) and ihpr2(18)     '  1   0
' set B production                '  1.5 
' istat=1 old istat>1 new         '  2                                    

There will be a file produced in the directory where you run it, which serves to ensure sequential numbering of the files being produced.

The output will be generated in the Ntuple format and the files named like evgen.1.nt, evgen.2.nt etc.

Using the Ntuple files

The staf/gstar executable has an adapter that reads such files. Within the staf session, one can issue a command like this one:
  • user/input user evgen.1.nt
and the use "trig" command to trigger events (i.e. propagate the in GEANT) one by one, or as many as desired.

The software component that reads the Ntuple format is contained in the gstar library that has to be loaded before reading the file, (see an example below).

One caveat that is important to not forget is the fact that if we allow all the spectator particles (ones at large rapidity) to propagate in the GEANT simulation, it becomes prohibitively slow as there will be a large number of extremely high energy interactions in the beam pipe and related structural elements around the beam, resulting in massive showers that are of no interest to us (because it all flies down the beampipe anyway), which take an enormous amount of CPU to compute.

This can be avoided by restricting the eta range, with the commands:

vsig 0.01 diamond
gkine -1 0 0 100 -eto eta 0 6.28 zleft zright

whereby eta should be replaced by a number like 6.3, and the zleft and zright should be actual cutoff numbers for the vertex distribution The diamond variable is the sigma of the gaussian distribution describing the interaction diamond Z-distribution.

To recap, the user may use this commands, as an example (assuming there are 100 events in the input Ntuple file):

detp geom year2003
make geometry
make gstar
gclose all
vsig  0.01  60.0
gkine -1 0 0 100 -6.3 6.3 0 6.28 -35.0 35.0
gfile o myoutput.fz
user/input user evgen.1.nt
trig 100

The resulting file myoutput.fz can now be used in the reco chain macro.

A note on Hijing 1.382

The Hijing Monte Carlo event generator has been updated with a new deutron model, starting with version 1.382. It is has been desided to run a GSTAR simulation for the 2003 d-Au run, with this newer version, for approximately one half of total statistics, the other half being done with the much older 1.33.
  • Simple graphs of the Hijing 1.33 vs.1.382 comparison The 1.381 designation in histogram titles is a typo and should be read 1.33. When looking at the ratios of particle species produced, keep in mind that the bins that exhibit "differences" have had insufficient statistics
This version shall be used in the year 2004 simulations as well.

Last updated by Maxim Potekhin on 08/10/2004