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Bugfix for FluxWeight and MeVPrtl #621

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Bugfix for FluxWeight and MeVPrtl #621

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0f08627
bugfix MeVPrtl to classify boone ntuple flux type as simple flux, and…
VCLanNguyen Jan 9, 2026
b34ca44
Change flux type from kSimple_Flux to kNtuple
VCLanNguyen Jan 27, 2026
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2 changes: 1 addition & 1 deletion sbncode/EventGenerator/MeVPrtl/Tools/BNBKaonGen_tool.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -311,7 +311,7 @@ simb::MCFlux BNBKaonGen::MakeMCFlux(const bsim::BooNe &boone) {
<< std::endl;
}

flux.fFluxType = simb::kDk2Nu;
flux.fFluxType = simb::kNtuple;
flux.fnimpwt = fBooneNtp.beamwgt;
flux.fvx = fBooneNtp.ini_pos[0][0]; //0
flux.fvy = fBooneNtp.ini_pos[0][1]; //0
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4 changes: 2 additions & 2 deletions sbncode/SBNEventWeight/Calculators/BNBFlux/FluxCalcPrep.cxx
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Expand Up @@ -224,7 +224,7 @@ namespace sbn {
}

//or do the above 3 lines in one line
// auto const& mclist = *e.getValidHandle<std::vector<simb::MCTruth>>(fGeneratorModuleLabel);
auto const& mclist = *e.getValidHandle<std::vector<simb::MCTruth>>(fGeneratorModuleLabel);
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@jicrespo jicrespo Jan 27, 2026

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If this line is only uncommented for the neutrino energy fix when MCFlux does not have a neutrino, I would move it to a block under if ( enu == -1 ). However, see my other comment about not fixing the energy in that case.

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@VCLanNguyen VCLanNguyen Jan 27, 2026 •
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There are several lines after this where mclist was commented out. So I'd like to keep at the same line for bookkeeping sake.


// If no neutrinos in this event, gives 0 weight;
int NUni = fParameterSet.fNuniverses;
Expand Down Expand Up @@ -264,8 +264,8 @@ namespace sbn {
}

// Collect neutrino energy; mclist is replaced with fluxlist.
// double enu= mclist[inu].GetNeutrino().Nu().E();
double enu= fluxlist[inu].fnenergyn;
if ( enu == -1 ) enu= mclist[inu].GetNeutrino().Nu().E(); //For MeVPrtl generator, not all MCFlux result in a neutrino, so equivalent neutrino energy is computed and saved as MCTruth
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@jicrespo jicrespo Jan 27, 2026

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If MCFlux does not contain a neutrino, it seems unnecessary to add a fake neutrino energy different from -1. I think it is safer to keep neutrino energy = -1 and handle the exception downstream.

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@VCLanNguyen VCLanNguyen Jan 27, 2026

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The flux SBND weight module needs the neutrino energy to compute the systematic, see line: https://github.com/SBNSoftware/sbncode/blob/develop/sbncode/SBNEventWeight/Calculators/BNBFlux/FluxCalcPrep.cxx#L276

The equivalent neutrino energy is computed by MeVPrtl here:

sbncode/sbncode/EventGenerator/MeVPrtl/Tools/IMeVPrtlFlux.h

Lines 127 to 136 in 8b07405

// Compute the equivalent neutrino energy for a given parent meson position / momentum
double EnuLab(double enucm, TLorentzVector meson_mom, TLorentzVector meson_pos) { // all in detector coordinates
// Assume neutrino travels to center of detector
double costh = meson_mom.Vect().Unit().Dot(-meson_pos.Vect().Unit());
// Scale factor
double M = 1. / (meson_mom.Gamma() * (1 - meson_mom.Beta() * costh));
return M * enucm;
}

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@VCLanNguyen VCLanNguyen Jan 27, 2026

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At the time being, the flux module would seg fault when the neutrino energy is missing or -1. So this fix is neccessary for at least the flux module to work with MeVPrtl inputs.

See @grayputnam 's comments from a while ago: https://github.com/SBNSoftware/sbncode/blob/develop/sbncode/EventGenerator/MeVPrtl/MeVPrtlGen_module.cc#L363-L371


//Let's make a weights based on the calculator you have requested

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