Rerun s21 over s20 MC about second-analysis-steps

[alexpearce]

This is great to have, thank you! Sounds like there are three things we need to add to the lesson:

1. A call-out saying something like “always contact your MC and stripping liaisons before restripping your MC. There may be details that are not covered in this lesson that you need to be aware of.”
2. Add the options files for the CALO reprocessing and a little explanation as to why they're needed.
3. Add the DefaultTrackingCuts and again explain why.

[acontu]

Glad to help!
Another small detail, not strictly related to this example is that if one wants to produce intermediate DSTs instead of going straight to ntuple extra options should be added to the DSTWriter conf as in:
https://svnweb.cern.ch/trac/lhcb/browser/DBASE/trunk/AppConfig/options/DaVinci/DV-Stripping21-Stripping.py

These options are at line 119 of the file above:
# Items that might get lost when running the CALO+PROTO ReProcessing in DV caloProtoReprocessLocs = [ "/Event/pRec/ProtoP#99", "/Event/pRec/Calo#99" ]
# Make sure they are present on full DST streams SelDSTWriterConf['default'].extraItems += caloProtoReprocessLocs

This is necessary to save the new protoparticles produced after the calo reprocessing (this will overwrite the previous one) so it is technically impossible to have a MC DST that is both consistent with s20 and s21.

[alexpearce]

Having a lesson on that would be very nice. We talked about it in the past in #7. I tried it in the past, but ran in to problems that I can't remember now. I'm +1 on getting the technique more widely known; it should make remaking ntuples much faster.