Proper madgraph settings for 5-flavor vs 4-flavor PDFs
Dear Madgraph5_aMC@NLO experts,
I would like to know more details about the proper madgraph settings for 4-flavor vs 5-flavor PDFs. From my previous understanding, in order to use a 5-flavor PDF (say, LHAPDF 263000), I need to do the following changes according to this thread [1]:
1) modify the definition of proton and jet in process card
2) modify the PDF, maxjetflavor, asrwgtflavor in run card
3) either modify b quark mass to zero in the parameter card or define a restrict card and put it in the UFO directory, import the model MODEL-no_bmass
However, while I try this change for a few mono-Higgs models, I notice a feature and I am not sure if it's OK: since the b quark mass is set to zero, for the (pseudo-) scalar mediators that have yukawa-like coupling, its coupling to b quark becomes zero. This also reduces the width of (pseudo-) scalar mediators slightly, not a lot. But now I wonder if it makes sense.
I mean I assume we only want to modify the mass of incoming b quarks, not the mass of the b quarks in the decays (outgoing b quarks)? Is there a way to do so in madgraph?
In addition, I also find for these models, no matter what I put in process card/run card/b quark mass, as long as LHAPDF is 5F PDF 263000, they give the same cross sections xxxx, when LHAPDF is 4 F PDF 263400, madgraph returns another cross section value yyyy, independent of the setting of b quark mass or proton/jet definition. I assume this is because for these models, the b-quark initiated process has very small contribution in the cross section to start with. So perhaps for these models, if there is no way to change only the mass of incoming b quarks, we could leave b quark mass at 4.7 GeV while using the 5F PDF?
Thanks!!
Shin-Shan Eiko Yu
[1]
https:/
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