Using generic biasing to boost cross sections in geant4_vmc

[janerhein]

Hello,

The Geant4 Documentation is quite extensive concerning the use of generic biasing:
https://geant4-userdoc.web.cern.ch/UsersGuides/AllGuides/html/ForToolkitDeveloper/GuideToExtendFunctionality/EventBiasing/eventBiasing.html
I also saw the possibility of adding the +biasing option in the TG4RunConfiguration, as can be seen in https://github.com/vmc-project/geant4_vmc/blob/b1442f7bbbf44617fbeca7fb2491eee76df121e0/examples/E03/g4tgeoConfig6.C
This should allow the use of generic biasing in a way compatible with the use of geant4_vmc.

However looking through some of the code, it seems this was implemented in a way to use icnlxx physics for some media.
I was not able to figure out how to use this method more generally in order to i.e. boost a certain cross section by a fixed factor.

Is this possible with the tools currently available in geant4_vmc? In any case I would be very grateful for some insights regarding this.

[ihrivnac]

Hello,

The current usage of generic biasing in Geant4 VMC is only for special needs of the ALICE experiment for using a different physics models in a selected detector region (= combining two physics list in the same application).

A general support for Geant4 generic biasing could be added via supporting user classes derived from Geant4 base classes for biasing (G4VBiasingOperator, G4VBiasingOperation); this approach would work only with Geant4, as the other geant4_vmc extensions. We could then choose one Geant4 extended examples from geant4/examples/extended/biasing and provide its VMC version in geant4_vmc.

Would the above fit your needs?

[janerhein]

Hello,

Overall that sounds very helpful. Especially since inheriting from G4VBiasingOperator and G4VBiasingOperation is quite generic and gives the user a lot of flexibility.
I think geant4/examples/extended/biasing/GB01 would be a good example to use. It demonstrates the use of generic biasing to alter the cross section of specific processes. I think the use case is also generic enough to provide a benefit for a number of users.
Thank you for the help.