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Forum: Biasing and Scoring
Re: None ExampleGB01 question (Carlos Ayerbe Gayoso)
Date: 07 Jan, 2015
From: Marc Verderi <Marc Verderi>

Dear Carlos,

You should indeed (in principle) bias the proton in your case : as, I 
understand, the pi+, mu+, etc. are produced by the interaction of the 

Now, compared to what you want, there are things to work on:
     - first, the biasing scheme as been essentially tested with neutral 
incident particles, it might work with charged, but this needs to be 
studied (and the problem you see BIAS.GEN.14 might be related to this), 
and is the next development step FY 2015.
     - I understand you want to bias specifically the production of pi+ 
etc. If you start with GB01, which is doing a cross-section change, all 
final states are "biased the same way" : ie the relative amounts of pi+, 
mu+, etc. stay the same. If you are fine with this then, cross-section 
biasing is adequate. If you want -say- to enhance pi+ production, then 
this is a final state biasing which is needed. This is possible today, 
but needs some extra work.
Please provide a bit more information about what you need.


On 01/07/2015 01:13 AM, Carlos Ayerbe Gayoso wrote:
> *** Discussion title: Biasing and Scoring
> Dear GEANTers
> this is a very simple question. I modified GB01 example to have protons
> of 1.2GeV over a carbon disk and biasing the production of pi+, mu+ and
> e+. Since is the first time I'm working wiht the biasing process, I just
> started quite naive.
> I changed the gun to have protons of 1.2 GeV, instead of neutrons as was
> originally.
> The detector is a carbon disk of 100mm radius and 5mm thickness.
> In the main file, I started to modify the bias section with:
> biasingPhysics->Bias("pi+"); biasingPhysics->Bias("mu+");
> biasingPhysics->Bias("e+");
> and something similar in the DetectorConstruction module:
> testMany->AddParticle...
> Just for fun I used the GUI to see the result visually and compare the
> option ON or OFF, with only pi+ particles visible. The visual output was
> the same in both cases. In other words, biasing didn't change anything
> at all.
> Then I figure out that neutrons were originally listed in the biaisng
> process, so I introduced the proton in the bias list
> biasingPhysics->Bias("proton");
> and it seems there is a change with the bias ON option comapred with
> previous runs (the OFF option seems to behave similar as before).
> Is this the correct way? I mean, should the primary particle be listed
> in the bias? why?
> Maybe everything is wrong since in the new one (with protons in the
> bias) I got the warnings:
> -------- WWWW ------- G4Exception-START -------- WWWW -------
> *** G4Exception : BIAS.GEN.14
>        issued by : G4InteractionLawPhysical::SetPhysicalCrossSection(..)
> Cross-section value passed is negative. It is set to zero !
> *** This is just a warning message. ***
> -------- WWWW -------- G4Exception-END --------- WWWW -------
> Thank you very much for your feedback
> Carlos Ayerbe
> -------------------------------------------------------------
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1 None: Re: ExampleGB01 question   (Carlos Ayerbe Gayoso - 07 Jan, 2015)
(_ Idea: Re: ExampleGB01 question   (Tom Roberts - 07 Jan, 2015)
(_ None: Re: ExampleGB01 question   (Carlos Ayerbe Gayoso - 08 Jan, 2015)
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