What is Hijing and how do I run it?
References
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 run.data 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.
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