[Halld-offline] halld_recon versioning

[Peter Pauli]

Hi everybody,

as Thomas already mentioned in the Analysis and Production meeting yesterday there is a problem the way most people probably use MCwrapper to produce their MC. The version.xml that can be specified contains a halld_recon version that should be chosen to match the halld_recon at the time of data production (for the latest reconstruction of spring17 that would be recon-2017_01-ver03_hdr as e.g. in version_recon-2017_01-ver03_8.xml). So the problem is that the analysis launches that produced the trees afterwards used more recent halld_recon builds with sometimes substantial changes to the analysis libraries. That means that if one produces MC with version_recon-2017_01-ver03_8.xml the reconstruction matches what was used for real data but the trees produced by ReactionFilter will not match what was produced in a subsequent analysis launch.
If this is a big or a small problem is very much channel dependent but surely we all agree that we want to be able to produce our MC such that it matches the trees that we analyse and not just the REST files. A quick fix to this problem is that each individual user needs to check the version.xml used for the analysis launch in question and rerun over the REST files produced by MCwrapper. This should yield the correct trees. Although this will work I don’t think it is a good solution in the long run and we should come up with something better in this working group.

Cheers,
Peter
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