Try to use source code files generated by (see the new “cor.C” for instructions on how to use them):
root -b -l -q DAT000002.root -e 'cor->MakeClass();'
UPDATE: I’m afraid you need to talk to your colleagues who are familiar with your data. @pcanal The source code generated by the TTree::MakeClass method (and other similar methods) will be broken/misbehaving for all variable size arrays in the non-split “Particle” branch.