Re: GEANT Branching Fraction Table

[Alexander Somov <somov@jlab.org>]

You have to recompile HDGeant (, i.e., parameters should be hardcoded).
You can overwrite the branching fractions in the uginit.F file
(in the Simulation/HDGeant directory) where geant is initialized:

      integer my_ipart
      real    my_bratio(6)
      integer my_mode(6)

      data my_bratio/0.0,0.0,0.0,0.0,0.0,0.0/
      data my_mode/0,0,0,0,0,0/

      ......

*             Initialize GEANT tracking structures
*
C..geant..
C     eta - > gamma gamma
      my_mode(1)   = 10100
C     Br = 100%
      my_bratio(1) = 100.0
      CALL GSDK(17,my_bratio,my_mode)
C     number 17 stands for eta

---------------------------------

Then, make.


When you start hdgeant you should get the message:
 *** GSDK ***: Warning, redefinition of decay for particle:
0Part                         Options        Mass    Charge    Life time      User words

   17 ETA                        3       0.5475E+00     0.    0.54850E-18



I've just generetaed a few events with eta's. It's forced to decay into 2
gammas. See also some details in the www page I've sent to you in my last
mail.

Cheers,
       Sascha








On Thu, 31 Jul 2008, Matthew Shepherd wrote:

>
> Sascha,
>
> Thanks -- yes, for PYTHIA, just the eta itself is passed onto GEANT.
> Do you know how to override the default decay branching fractions in
> the code?
>
> I see that (unfortunately) GEANT has builtin a non-zero branching
> fraction for eta -> pi^0 gamma gamma which one of the rare signal
> mdoes that Liping is interested in.
>
> -Matt
>
>
> On Jul 31, 2008, at 3:07 PM, Alexander Somov wrote:
>
> >
> > http://wwwasdoc.web.cern.ch/wwwasdoc/geant_html3/node73.html#DRAW001
> > (the same table is in geant 3.21 manual)
> >
> > (I am not sure that your eta decays in geant; it might decay
> > in the event generator directly (?))
> >
> > Sascha
> >
> >
> > On Thu, 31 Jul 2008, Matthew Shepherd wrote:
> >
> >>
> >> Hi,
> >>
> >> Can anyone tell me where the branching fraction table for eta's is
> >> coded into GEANT3?
> >>
> >> Thanks!
> >>
> >> -Matt
> >>
> >>
> >
>
>