NLO ickkw and MadSpin (spin correlations and off shell effects)
Dear MadGraph5_aMC@NLO team,
I'm generating a single process:
generate p p > t t~ [QCD]
1. First, in the run_card, what should I use for "ickkw"? From earlier discussions, I found that if I'm not generating multiple processes (i.e. add process p p > t t~ j [QCD]), I don't need to turn on ickkw, since there is no double-counting issue. So I'm using ickkw = 0. Can you please confirm this?
# 0: No merging
# 3: FxFx Merging -
# 4: UNLOPS merging (with pythia8 only).
# -1: NNLL+NLO jet-veto computation. See arxiv:1412.8408 [hep-ph].
2. Second, it looks like I cannot decay tops in [QCD] mode. It looks like I have two options, decaying tops either in MadSpin or Pythia8. For MadSpin, I'm using the following syntax in madspin_card.dat, for di-leptonic decays:
define lepton+ = l+ ta+
define lepton- = l- ta-
decay t > w+ b, w+ > lepton+ vl
decay t~ > w- b~, w- > lepton- vl~
launch
Does this take into account a full spin correlation of tops (1405.0301)? Can you please confirm it?
Also does this take into account off-shell effects of tops and W bosons? Can you please confirm it? The syntax I used work at generation-level is "t > b lepton+ vl" which include both on-shell and off-shell effects, but the same syntax didn't work in MadSpin.
Finally, if I decay tops using Pythia8, does this take into account spin correlations and off-shell effects? Is there a difference between using MadSpin and Pythia8?
Thank you in advance!
Sincerely
Saurabh
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