Production process of particles with TVirtualMC

Dear all,

I am trying to figure out how to get the production process of a particle in an event in O2.
The TVirtualMC class
https://root.cern.ch/doc/v622/classTVirtualMC.html#ac6254d237d7179a695b15c8e4c7a7dc4
has a function ProdProcess()
https://root.cern.ch/doc/v622/TMCProcess_8h_source.html
Which takes the parameter Int_t isec. Does anyone know what this parameter is?

Is this the way to figure out via which production process the current particle is produced?

Kind regards,
Cas