The popular GENIE Generator product is used by nearly all accelerator neutrino experiments and it plays a key role in the exploitation of neutrino data. The Generator implements a modern software framework and it includes state-of-the-art physics modules. It captures the latest results of the GENIE global analysis of neutrino scattering data and includes several tunes that were produced using the proprietary Comparisons and Tuning products. The GENIE physics model is universal and comprehensive: It handles all neutrinos and targets, and all processes relevant from MeV to PeV energy scales. The Generator includes several tools (flux drivers, detector geometry navigators, specialized event generation apps, event reweighting engines) to simulate complex experimental setups in full detail and to support generator-related analysis tasks.
The polarization vector of the primary lepton seems to be set to -1 (antiparallel to the momentum vector), regardless of the energy of the lepton (based on this code). This approximation is correct for high energies but not for lower energies, e.g., when 5 GeV tau neutrinos produce tau leptons.
It seems like there is a suggestion in a comment in the code to implement a more sophisticated calculation of the polarization. This feature would be helpful, especially as lower energy neutrinos and tau production become more important.
Are there any current plans for when this polarization is planned to be implemented?
In the mean time, it would be useful if a warning is raised or it is written explicitly in the documentation that:
the polarization vector is always antiparallel to the momentum
the polarization vector is in the lab frame (not in the lepton rest frame, as one might assume)
the current approximation is correct for high energies ($E >> m_l$) but not otherwise.
Thank you for your help and consideration of this request!
Dear Simon,
Yes, we have a plan to implement polarization, but, you know, the common problem of lack of time. But since the request has been received, work in this direction will be accelerated.
idkakorin
commented
3 months ago 
simonthor
The polarization vector of the primary lepton seems to be set to -1 (antiparallel to the momentum vector), regardless of the energy of the lepton (based on this code). This approximation is correct for high energies but not for lower energies, e.g., when 5 GeV tau neutrinos produce tau leptons.
It seems like there is a suggestion in a comment in the code to implement a more sophisticated calculation of the polarization. This feature would be helpful, especially as lower energy neutrinos and tau production become more important.
Are there any current plans for when this polarization is planned to be implemented?
In the mean time, it would be useful if a warning is raised or it is written explicitly in the documentation that:
Thank you for your help and consideration of this request!