swertz
commented
3 years ago Hi Matthew,
then produce all the simulated events with the toolchain and then come back and have MoMEMta use that same generation process in combination with MoMEMta-MaGMEE to have MoMEMta know what was done?
That is correct. In MoMEMta it is basically assumed that you already have your events (simulated or data), and that you need to compute weights for them.
In your case it indeed comes down to generating the process in MG5 and writing out the C++ matrix element for MoMEMta on the one hand, and generating events using the MG5 toolchain (madevent, then Pythia or Delphes or whatever), with the same original generate command in MG5, on the other.
Note that in general there is no relationship between the two: you can compute weights under any process hypothesis, not necesseraly the same that was used to generate your events (in fact, when you compute weights on data, you don't know how the events were produced!). Very often the generator used is also different, i.e. you can very well compute weights under the hypothesis of leading-order ttbar production (with a matrix element coming from MoMEMta-MaGMEE), whereas the events were simulated using powheg at NLO.
Does this clarify things?
FlorianBury
matthewfeickert
Hi @swertz @FlorianBury. I have a question that by definition is going to be pretty dumb RE: using MoMEMta and MoMEMta-MaGMEE that will probably be obvious once I have time to reread the "In depth sections of https://momemta.github.io/ and https://arxiv.org/abs/1805.08555 and https://arxiv.org/abs/2008.10949. (Or maybe I'm confused on the Lua configuration process.)
If this doesn't make, please ask for clarification as I'm writing this Issue somewhat quickly.
How does one practically go from the MadGraph5 process and building the matrix elements with MoMEMta-MaGMEE to producing simulated events to the computation of weights?
The examples that are given in the tutorial repo (c.f.
run_ttbar_tutorial.sh) start out with provided MatrixElements and a simulated event file to read in (Tutorials/TTbar_FullyLeptonic/tt_20evt.root). That all works fine, and those simulated events are generated using MG5_aMC@NLO, Pythia and Delphes.However, as a starting example, I'd like to be able to start with just the MadGraph5 process and have MoMEMta-MaGMEE produce the matrix element
if I want to be able to use MoMEMta with these matrix elements it isn't clear to me the in between steps required. Would I need to take that same MadGraph5 generation
and then produce all the simulated events with the toolchain and then come back and have MoMEMta use that same generation process in combination with MoMEMta-MaGMEE to have MoMEMta know what was done?
I think this is probably rambly enough to have lost any clarity, but I guess I'm missing the connecting step of the requirements on event simulation and connecting simulation back to MoMEMta.