Event Input


There are several ways to simulate passage of particles through  described detector volume. For this purpose one can specify the set of particles "by hand" by means of user's menu command, or use input from the event generator (such as HIJING or VENUS), or Mickey-mouse generator.

For the first case,  one can use the command

user/phasespace [ ntrack id ptlow pthigh ylow yhigh philow phihigh ]       Where

ntrack -  Number of tracks per event. Default value is 100.
id       Geant Particle ID. Default value is 8.
ptlow   - Lower limit of pT. Default value is 0.
pthigh - Upper limit of pT. Default value is 1.
ylow    - Lower limit of rapidity. Default value is -1.
yhigh   - Upper limit of rapidity. Default value is 1.
philow  - Lower limit of phi. Default value is 0.
phihigh- Upper limit of phi. Default value is 6.283

By this command one can generate flat phase space in place of input file of events.  Parameters are Geant PID, lower and upper bounds of rapidity interval, lower and upper  bounds of pT interval, and number of tracks per event. Full azimuthal  interval is used.  If no parameters are  given, old values existing in the program are preserved.  Initial limits   are 0< pT<10000, -10<y<+10, 0<phi<2pi.
For example the command line

phasespace 1 8  0.1  1 -1 1

will create one pion  with  randomly chosen pT  in the range  1000 Gev< pT<10000GeV, rapidity in the range +/-1.

The simple kumac example, which runs standard gstar session and propagates one pion through loaded simulated detector modules, can be found here.

In order to use as an input file, created by one of event generators,  one needs to specify input and almost always output files (to keep the data) for the GSTAR session.  There are some examples of kumacs for running events from HIJING and Venaus. There are two simple commands that provide this  settings. One can use:

user/input  user file_name1 file_name2

to specify the input file/files name and type.  Opens one or two files of events as input to GSTAR.  There are few possible values for the type option: fz, tx, fztx, txold, txotx, fztxo.
If read types fz  (Zebra) or tx (Star new text format) are given, only one file of the given   type is opened using the first input filename. If read type fztx or txotx  is given, two files are opened and merged within Geant. For the fztx  option, the first filename must be a fz-file and the second filename a tx-file (new text format). For the txotx, the first file must be an old format text file and the second a tx-file, and so on. The detailed description of Geant input file formats can be found here.

For the beginner it is a good idea to use a simplest way to specify the input:

user/input  auto file_name

(It is possible to use any other word instead of auto; it should just vary from reserved option mention above). In this case the input data types are defined by the first letter of the file extension:
.t  means any text format,
.x - any xdf format,
.s - staf particle table (HEPEVNT),
.m - mickey-mouse event generator.

To set up the input file one can use the command

user/output action file_name

The possible action values are o or c, open or close the selected file correspondingly.

In order to run mickey-mouse event generator one should load  a module  gstar_micky.g - a simple "mickey-mouse" generator distributing particle like pions, kaons and protons etc. throughout  phase space in a pseudo-realistic way. Each specie is generated with a given average multiplicity, pt spectrum slope and rapidity width.
For positive mean multiplicity input, Poisson distribution is used to generate actual particle number per event. A negative     multiplicity input means exact number of particles per event (no fluctuations).  All parameters, including the list of generated species (up to ten) can by changed via DETP commands. Default  parameters can be found in the file itself.
Following is an example of the DETP command which sets the micky-mouse generator for pi+, pi-, K+, k- and protons with  following multiplicities, pt spectrum slopes (c/Gev) and Gaussian width of rapidity distribution:

           DETP micky miky.np=5
             code=  8   9   11 12 14
             mult=  100 100 10 10 10
             slope= 5   5   4  4  3.3
             dy=    2   2   2  2  2

Here is  example of kumac for running mickey-mouse event generator.