A Question on Getting Weights for Different Combinations of Final State Particles

[jeonghan1000]

Dear MoMEMta team,

Thanks a lot for sharing MoMEMta code to public. I have recently migrated from MadWeight to MoMEMta, and want to know more about features of MoMEMta.

In particular, I would like to get two different weights from two different ways of pairing b-quarks and leptons in di-leptonic ttbar events. The authors kindly put an example code "tt_fullyleptonic.cc". The authors explained (https://arxiv.org/abs/1805.08555) that MoMEMta considers all possible combinations and takes an average of weights. Since for my purpose I didn't want that, so I turned off this feature by setting:

lua_parameters.set("USE_PERM", false);

Then I compute two weights as following:

---

// combination 1
MoMEMta weight(configuration.freeze());

// Electron
Particle electron { "electron", LorentzVector(lep1.Px(), lep1.Py(), lep1.Pz(), lep1.E() ), -11 };
// b-quark
Particle b1 { "bjet1", LorentzVector( bjet1.Px(), bjet1.Py(), bjet1.Pz(), bjet1.E() ), 5 };
// Muon
Particle muon { "muon", LorentzVector( lep2.Px(), lep2.Py(), lep2.Pz(), lep2.E() ), +13 };
// Anti b-quark
Particle b2 { "bjet2", LorentzVector( bjet2.Px(), bjet2.Py(), bjet2.Pz(), bjet2.E() ), -5 };

std::vector<std::pair<double, double>> weights = weight.computeWeights({muon, electron, b1, b2});

---

Now to get the weight from the other combination, I just swapped the momenta of two b-quarks:

---

// b-quark
Particle b1 { "bjet1", LorentzVector( bjet2.Px(), bjet2.Py(), bjet2.Pz(), bjet2.E() ), 5 };

// Anti b-quark
Particle b2 { "bjet2", LorentzVector( bjet1.Px(), bjet1.Py(), bjet1.Pz(), bjet1.E() ), -5 };

---

and computed the weight:

std::vector<std::pair<double, double>> weights = weight.computeWeights({muon, electron, b1, b2});

Could you please give me some comment on whether it is correct thing to do? Should I make an additional change?

Thank you very much.

Best wishes,

Jeonghan