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At Fermilab: no in-person presence at the lab for this meeting
Erica Snider: Release and project report
Wes: SBN planning to cut a production release this week or next. Are there changes that SBN would care about, eg, optimization of some sort? They would prefer to factorize this change with the on-going push to cut the release?
Do not know off hand. Kyle would know, but is away. Suggested checking the release notes.
SBN has tested online with art 3.09. Plans to work from production in LArSoft, so anticipates moving to art 3.09 at some point soon.
Robert Hatcher: The option for Pythia 8 decays of tau and charm-hadrons in non-Legacy LArG4
Follow-up from past talks.
Discussed then the inability of Geant4 to properly decay charm and tau
If G4 was handed one of these particles, it would get to the decay point, then disappear
All sorts of problems ensue from that
Dealt with in past by having Genie decay them (via integrated pythia6) before handing them off to G4
This produced the decay products, but the tau and charm particles were not tracked, so produced a gap between the production and decay points
Nonetheless, was sufficient for some experiments (eg, NOvA) since offset was small, and energy is conserved
LArSoft had same solution available
Eventually used by DUNE
Not by MicroBooNE
Unsure about other LArSoft experiments
This Genie feature was controlled via GENIE XML configuration file packaged as genie_phyopt UPS product
dkcharmtau or dkcharm qualifiers
But the gap was a problem, so...
G4 started to decay taus, but only at minimal level
Not sophisticated. Possibly phase space only?
Also had some bugs that messed up momentum calculation in cases
So still no solution that simultaneously got the decay and the detector simulation parts right
A better solution
Let G4 do it's job, and use G4's plug in features to provide alternative for decaying tau and charm
Ideally, make it "semi-automatic", or otherwise easy to configure in LArSoft with little coding needed
The new solution makes use of G4 extensible physics list factory to supplement regular standard physics lists
so "FTFP_BERT " becomes "FTFP_BERT+PY8TAUDK+PY8CHARMDK"
What does PY8TAUDK do?
Removes G4's default decay table for taus
Register taus to be decayed by Py8TauDecayer, which is a G4VPhysicsConstructor with and interface to pythia8
via an instance of G4VExtDecayer : Py8Decayer
lives in nug4/AdditionalG4Physics
Similarly, PY8CHARMKD does the same for PDG code signaling charm (or bottom) quarks
NOTE: Both also register any other particles that don't already have a decay table in G4 to use pythia8 as well
Limitations
Works only in non-Legacy LARG4 because it relies ion the extensible physics list factory supplied by G4 (which is not in Legacy LArG4)
Also FTFP_BERT+PY8TAUDK == FTFP_BERT+PY8TAUDK+PY8CHARMDK,
BUT: FTFP_BERT+PY8CHARMDK != FTFP_BERT+PY8TAUDK+PY8CHARMDK
Requires some changes to fcl
Need to switch to using the larg4Main module
Provided config example for that
Need to change the "PhysicsList" configuration to use the new things as noted above
Status of this better solution
Julia Yarba implemented the interface to Pythia8 in stand-alone G4 app
Robert integrated into the factory system so that physics process can be added by configuring the PhysicsList name, and integrated it into nug4 (with a link in larg4)
Issues
Integrated into NuG4 package (to be avail with art 3.09)
added dependence on Pythia8
Genie sets tau polarization for RES+DIS, but not QES in it's event record (to be fixed in v3_02)
polarization info is in MCTruth in LARSoft event record, and transferred to G4PrimaryParticle
nub4/ConvertMCToG4 and larg4/pluginActions/MCTruthEventAction_service.cc
Linked to LArG4main to get library loaded at run time
nothing needs to be done on user side other tan load the library to make it available; no explicit compile / link time refs
Possible to do the same kind of interface for the tauola package.
Pythia8 documentation implies that the decay models are slightly different in some cases
See https://indico.cern.ch/event/300387/contributions/686167/attachments/565826/779490/ilten140915.pdf