[Halld_src] Update/reminder on FCAL shower position reconstruction

[Igal Jaegle]

All,

The FCAL energy & time calibrations of this data set are done using the same method than for the two previous PrimEx-eta data sets. This method is different than what is used in the GlueX data sets.

In short, it means:
1/ Position of the shower is reconstructed by taking the average positions of all modules in the cluster logarithmically weighted by their energy
To enable this reconstruction in high-level objects add this line in your jana configuration file:

FCAL:SHOWER_POSITION_LOG 1
(available since yesterday on the GIT master branch)

If not used, the FCAL pi0 mass will be shifted to lower mass by 2 to 3 MeV.

2/ Ring wise energy dependence correction but since this correction is not applied yet add this line in your jana configuration file:
FCAL:LOAD_NONLIN_CCDB 0

tks ig.

PS: the final FCAL calibration will start once the data taking is over.
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