Incorrect polarization vector for primary leptons

[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:

• 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!

[idkakorin]

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.

[simonthor]

Thank you for the update! That is of course understandable that other features are sometimes prioritized.