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Forum: Physics List
Re: Question Anti-Proton Physics (Michael Douglass)
Re: Question Re: Anti-Proton Physics (Dipanwita Banerjee)
Date: 11 Sep, 2013
From: John Apostolakis <John Apostolakis>

Dear Dipanwita,

  For the G4QCaptureAtRest process, it is the CHIPS model which is 
handling the interactions. As with any model you can look at the 
description in the Physics Reference Manual; in this case you should 
also refer to  the original papers by
    M. Kossov, P. Degtiarenko and H.P. Wellisch
  circa 2002-03 for a description of the underlying model.

You seem to hope to adapt the implementation/code which exists. This is 
possible, since the source code is available.  However it is likely very 
difficult to make changes to the model and corresponding changes to the 
code without care and expert advice.   I suggest to contact its author 
M. Kossov via his CERN email, in case he is able and willing to give you 
guidance in this regard.  Since a physics model has several parameters, 
it can be hard for someone who is not very-very familiar with the model 
and code to do this - e.g. to decide on the appropriate range of 
parameters for tuning and to compare to the relevant data for 
constraining and fixing these parameters, if such data exists.

However it would likely be more productive to use instead a new version 
of Geant4, with an FTFP-based physics list.  I suggest using Geant4 9.6 
patch 02 with the FTFP_BERT physics list, which is the recommended list 
for several domains, including HEP and nuclear physics.

It may be, though, that your requirements cannot be met by our current 
models - there are limits both to their underlying assumptions and to 
the calculations/tuning which the authors were able to undertake.  In 
this case I would suggest to seek alternative  approaches, either 
modeling or parameterising data which you have been able to measure, in 
case this would allow you to fulfill your application's requirements.

Best regards,
John Apostolakis

On 7/5/13 9:01 AM, Dipanwita Banerjee wrote:
> *** Discussion title: Physics List
> Hello
> I am trying to look into the tracks of the secondaries produced by
> antiproton annihilations. In principle I am just interested in the
> mesons produced as a result of the annihilation. My beam energy would be
> <1kev. I am using G4QCaptureAtRest for the process which is giving me
> the pions but also other particles as a result of the nuclear
> fragmentation that's a part of the QCapture algorithm. I would like to
> get rid of this part and just have the pions, as a part of the pions are
> being absorbed by the nucleus of the target which is causing the
> fragmentation and that's causing me to loose few pions in the result. I
> don't want that. My geometry is fairly simple. It has a 2mm titanium
> target followed by a tracker with Argon Gas.
> Can anyone tell me if there's a better process that can give me the
> correct production rate of the pions? Or maybe I can change the
> G4QCaptureAtRest process to meet my requirements. I would like to have
> the explanation of the code in G4QCaptureAtRest as I am a little
> confused how they have defined the annihilation and the fragmentation.
> Can anyone please tell me where I can find the explanation or maybe give
> me an idea how they have defined the code?
> Thanks,
> Dipanwita
> -------------------------------------------------------------
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