Bertrand Martin Dit Latour authored Oct 05, 2020 and Vakhtang Tsulaia committed Oct 05, 2020

Hello,

This MR is harmonising the use of tau track IP and IP significance parameters across the tau reconstruction.
We now use everywhere the impact parameters w.r.t. the tau vertex instead of w.r.t. beam line (relevant for d0).
New methods are introduced to retrieve the track IP and IP significances directly from the tau track (before, we would use e.g. d0 from the associated TrackParticle, i.e. d0 w.r.t. the beam line).

Because we need track IPs early in the reconstruction (right after tau vertex finding and tau track association, and before tau track classification), I had to move the track IP calculation from TauVertexVariables to TauTrackFinder, as TauVertexVariables is scheduled late in the reconstruction chain.

Two variables have been discontinued: TauJetsAux.ipSigLeadTrk TauJetsAux.ipZ0SinThetaSigLeadTrk. These are track IPs defined for the leading track. Now that we compute these for all tau tracks, we can drop these "leading track" variables.

Using standalone tau reconstruction from ESD, I have checked that the tau reconstruction output is unchanged if I fall back to the "old" calculations for track IPs, i.e. if I set d0TJVA = track()->d0(), and z0sinthetaTJVA = z0sinThetaTJVA(tau) in Track_v1.
Meaning, this MR is mostly code reorganisation. The only modification that changes the reconstruction is the new definition of d0TJVA and z0sinthetaTJVA.
With these new definitions, we get slight changes on the BDT ID score and the RNN ID score, as well as the track classification scores, as expected.

Cheers,
Bertrand