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https://lhcathome.cern.ch/lhcathome/result.php?resultid=272228758
Theory_2390-1112673-0_0
===> [runRivet] Fri May 1 23:05:05 UTC 2020 [boinc pp jets 7000 20,-,210 - pythia8 8.301 vincia-default 100000 0]

This Pythia is now running for more than 9 h.
So far it produced a logfile >210 MB with 3.338.311 lines.
Nearly all lines show a warning like this:

 Pythia8ToHepMC::fill_next_event: inconsistent mother/daugher information in Pythia8 event 
i = 9 mother = 7
 This warning can be turned off with the Pythia8ToHepMC::print_inconsistency switch.
 Pythia8ToHepMC::fill_next_event: inconsistent mother/daugher information in Pythia8 event 
i = 12 mother = 10
 This warning can be turned off with the Pythia8ToHepMC::print_inconsistency switch.
 Pythia8ToHepMC::fill_next_event: inconsistent mother/daugher information in Pythia8 event 
i = 18 mother = 16

Thanks computezrmle for alterting us to this.

I've committed a temporary fix to silence these warnings, which should go out in production runs soon.

The problem arises because we introduced a new "bremsstrahlung shower" model into Pythia 8.301, called Vincia. (Previously distributed as a stand-alone plug-in to Pythia.) That model has different "mother-daughter" relationships - "mothers" here referring to particles that act as sources of bremsstrahlung, while "daughters" refer to the emitted quanta. (Vincia is based on a so-called "antenna" model of radiation, while Pythia's default model is based on something more like individual charges.) Internally, the new model is self-consistent, but the consistency check made in the output interface for event analysis has not yet been updated to "accept" these new alternative relationships. So, we think the events you are generating are actually OK - but the output interface doesn't realise it and issues a warning. We will correct that in an upcoming version, probably 8.303 or 8.304, but until then I have activated the flag mentioned in the message you saw, to silence this particular warning.

Thanks again,
Peter Skands